bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic Response of Blades Having Three-Dimensional Nonlinear Shroud Constraints
Authors: Chen J. J. , Menq C. H.
Published: July 2002

In this paper, a three-dimensional shroud contact model is employed to predict the periodic response of blades having three-dimensional nonlinear shroud constraint. When subjected to periodic excitation, the resulting relative motion at the shroud contact is assumed to be periodic in three-dimensional space. Based on the three-dimensional shroud contact model, analytical criteria are used to determine the transitions between stick, slip, and separation of the contact interface and are used to simulate hysteresis loops of the induced constrained force, when experiencing periodic relative motion. The constrained force can be considered as a feedback force that influences the response of the shrouded blade. By using the multiharmonic balance method along with Fast Fourier Transform, the constrained force can be approximated by a series of harmonic functions so as to predict the periodic response of a shrouded blade. This approach results in a set of nonlinear algebraic equations, which can be solved iteratively to yield the periodic response of blades having three-dimensional nonlinear shroud constraint. In order to validate the proposed approach, the predicted results are compared with those of the direct-time integration method. The resonant frequency shift, the damping effect, and the jump phenomenon due to nonlinear shroud constraint are examined. The implications of the developed solution procedure to the design of shroud contact are also discussed.
A Numerical Method for Bubbly Flow Simulation Based on a Multi-Fluid Model
Authors: Tomiyama Akio , Shimada Naoki
Published: July 2002

A numerical method based on an N+1-fluid model is proposed for the prediction of a three-dimensional unsteady turbulent bubbly flow with nonuniform bubble sizes. Among the N+1 fluids, one fluid corresponds to the liquid phase and the N fluids to bubbles. The model can therefore take account of N different bubble sizes. Since the fluid density of each bubble group can differ from that of other groups, the method is also applicable to multi-component flows such as a gas-liquid-solid flow and a liquid-solid flow with various particles. The increase in the number of fluids to be solved does not require any lengthy complicated programming because the calculation of N field equations for the gas phase is easily conducted using a single DO-loop. To demonstrate the potential of the proposed method, unsteady bubble plumes in a water-filled vessel were simulated using the N+1-fluid and two-fluid models. As a result, it was confirmed that the N+1-fluid model gave better predictions than the two-fluid model for bubble plumes with nonuniform bubble sizes.
A New Approach to the Effect of EP Additive and Surface Roughness on the Pitting Fatigue of a Line-Contact System
Authors: Chou Chau Chang , Lin Jen Fin
Published: July 2002

A gear-cam adaptor was used to investigate the effect of an extreme pressure (EP) additive in the base oil and roller’s surface roughness on the pitting life of a disk specimen under oil lubrication with rolling-sliding line contacts. Incorporating the mean friction coefficient, increases in the Vickers microhardnesses within the layer of strain hardening can explain the influence of the EP additive on the material toughness of the ratchetting layer. The pull-off forces obtained from the tip/sample’s force-distance curve of an atomic force microscopy (AFM) can further reveal the ever-growing characteristic of the boundary layer, which is benefit to retard the growth of cracks. Weibull plots for disk’s pitting life are provided for three lubrication cases. The use of the EP additive in the base oil can expand the range of pitting-life distribution; on the other hand, increasing the roller’s surface roughness can also elevate the pitting life of the specimen lubricated by the same oil. From the study of contact subsurface, the distributions of four material responses: boundary layer, ratchetting layer, shakedown layer, and elastic layer, can be found. The EP additive in the base oil affects the behavior of the first two layers and roller’s surface roughness, the dominant factor, even does the third one.
Effect of a Dent on the Pressure Distribution in Dry Point Contacts
Authors: Coulon, S. , Ville, and F. , Lubrecht A. A.
Published: July 2002

Using a dry point contact model, a parametric study of the peak pressure due to a dent was performed. The parameters varied were the dent depth and diameter. The numerical analysis ws complemented by an analytical analysis. Using the elastic body hypothesis, the study of the dented contact shows that various configurations can occur. Introducing the parameters SC1, a dimensionless pressure parameter and SC2, a dimensionless dent geometry parameter, the pressure peak in all these configurations can be represented in a single graph.
Dynamic Analysis of Anisotropic Cylindrical Shells Containing Flowing Fluid
Authors: Toorani M. H. , Lakis A. A.
Published: July 2002

This paper deals with the study of dynamic behavior of anisotropic cylindrical shells, based on refined shell theory, subjected simultaneously to an internal and external fluid. In the present theory, the transverse shear deformation effect is taken into account, therefore, the equations of motion are determined with displacements and transverse shear as independent variables. The solution is divided into three parts: In Section 2, the displacement functions are derived from the exact solution of refined shell equations based on orthogonal curvilinear coordinates. The mass and stiffness matrices of each structural element are derived by exact analytical integration. In Section 3, the velocity potential, Bernoulli’s equation and impermeability condition have been applied to the shell fluid interface to obtain an explicit expression for fluid pressure which yields three forces (inertial, centrifugal, Coriolis). Numerical examples are given in Section 4 for the free vibration of laminated composite and isotropic materials for both open and closed circular cylindrical shells. Reasonable agreement is found with other theories and experiments.
A Comparison of Homogenization and Averaging Techniques for the Treatment of Roughness in Slip-Flow-Modified Reynolds Equation
Authors: Jai M. , Bou-Saı¨d B.
Published: July 2002

This article is concerned with the simulation of a magnetic storage device consisting of a flying head above a rigid rotating disk. The need to improve the transfer rate has led, at present, to very small surface-to-surface distances (air gaps). In this situation it is compulsory to take into account roughness effects. A popular method consists in averaging film-thickness from Mitsuya et al. (1989), with good reported results compared with experimental data. To overcome some limitations that become apparent at very small air gaps, notably when the roughness is two-dimensional, Jai in 1995 introduced a new technique based on a rigorous homogenization theory. Recent developments from Buscaglia and Jai (2000) have greatly reduced the computational complexity of the homogenization-based method, rendering it suitable for practical applications. We propose in this paper an original approach based on strength and rigorous mathematical model to avoid numerical problems which are usually encountered in classical approaches. The validation of the homogenization-based method is in some sense, a generalization of the film-averaging technique suitable for configurations in which some parameters of the latter (such as the Boltzmann correction factor) are not unambiguously defined.
An Investigation on the Use of Connors’ Equation to Predict Fluidelastic Instability in Cylinder Arrays
Authors: Price Stuart J.
Published: July 2002

The use of Connors’ equation, or variations thereof, to predict the velocity at which fluidelastic instability occurs in cylinder arrays subject to cross-flow has become ubiquitous. The implicit assumption being that this equation accurately models the physics of fluidelastic instability, and all that is required is to find the “correct” value of Connors’ constant. The evidence for and against this assumption is examined in this paper. Other theoretical models of fluidelastic instability are reviewed and compared with Connors’ analysis. In addition, evidence from experimental data is considered. It is concluded that there are many deficiencies associated with Connors’ equation, and that if better “design guides” are to be obtained, more emphasis must be put on examining the physics of fluidelastic instability.
Geometry Effects on Turbulent Flow and Heat Transfer in Internally Finned Tubes
Authors: Liu Xiaoyue , Jensen Michael K.
Published: July 2002

A parametric study has been performed on turbulent flow and heat transfer in internally finned tubes. For a rectangular fin profile, the effects of fin number N, fin width s, fin height H, and helix angle γ were numerically investigated for the conditions of N=10∼40,H=0.03∼0.1,s=0.05∼0.22,γ=10 deg∼40 deg, and Re=40,000. In addition, the performance of three fin profiles—rectangle, triangle, and round crest—with the same fin heights, width, and helix angles were compared for Reynolds numbers between 10,000 and 70,000. Rectangular and triangular fins behave similarly; for some geometric conditions the round crest fin has lower friction factors and Nusselt numbers (17 and 10 percent, respectively) than the rectangular fin. However, when the number of fins is large, the round crest fin can have larger friction factors (about 16 percent). Damping of turbulence energy in the interfin region is credited for the reversal of the typical trends.
Multi-Blade Row Interactions in a Transonic Axial Compressor: Part I—Stator Particle Image Velocimetry (PIV) Investigation
Authors: Sanders A. J. , Papalia J. , Fleeter S.
Published: July 2002

Multi-blade row interactions in an advanced design 1&1/2 stage axial-flow compressor are experimentally investigated at both subsonic and transonic rotor operating conditions using particle image velocimetry (PIV). Transonic rotor operation had a significant impact on the downstream stator unsteady flow field due to phenomena associated with the intra-stator transport of the chopped rotor wake segments. In the stator reference frame, the rotor wakes have a slip velocity relative to the mean flow that causes the low-momentum wake fluid to migrate across the vane passage and accumulate on the stator pressure surface as the chopped wake segments are transported downstream. This results in the generation of counterrotating vortices on each side of the chopped wake segment that convect downstream with the mean flow and act as an additional source of unsteadiness to the vane pressure surface. These interaction phenomena are not evident in the PIV data at the part-speed compressor operating condition due to the much lower velocity deficit and hence slip velocity associated with the subsonic rotor wakes.
Effects of Frictional Loss on Bicycle Chain Drive Efficiency
Authors: Spicer James B. , Richardson Christopher J. K. , Ehrlich Michael J. , Bernstein Johanna R. , Fukuda Masahiko , Terada Masao
Published: July 2002

Chain drive efficiency has been studied to understand energy loss mechanisms in bicycle drive trains, primarily for derailleur-type systems. An analytical study of frictional energy loss mechanisms for chain drives is given along with a series of experimental measurements of chain drive efficiency under a range of power, speed and lubrication conditions. Measurements of mechanical efficiency are compared to infrared measurements indicating that frictional losses cannot account for the observed variations in efficiency. The results of this study indicate that chain tension and sprocket size primarily affect efficiency and that non-thermal loss mechanisms dominate overall chain drive efficiency.
Thermo-Economic Analysis of an Intercooled, Reheat and Recuperated Gas Turbine for Cogeneration Applications–Part I: Base Load Operation
Authors: Bhargava R. , Bianchi M. , Negri di Montenegro G. , Peretto A.
Published: July 2002

This paper presents a thermo-economic analysis of an intercooled, reheat (ICRH) gas turbine, with and without recuperation, for cogeneration applications. The optimization analyses of thermodynamic parameters have permitted to calculate variables, such as low-pressure compressor pressure ratio, high-pressure turbine pressure ratio and gas temperature at the waste heat recovery unit inlet while maximizing electric efficiency and “Energy Saving Index.” Subsequently, the economic analyses have allowed to evaluate return on the investment, and the minimum value of gross payout period, for the cycle configurations of highest thermodynamic performance. In the present study three sizes (100 MW, 20 MW, and 5 MW) of gas turbines have been examined. The performed investigation reveals that the maximum value of electric efficiency and “Energy Saving Index” is achieved for a large size (100 MW) recuperated ICRH gas turbine based cogeneration system. However, a nonrecuperated ICRH gas turbine (of 100 MW) based cogeneration system provides maximum value of return on the investment and the minimum value of gross payout period compared to the other gas turbine cycles, of the same size and with same power to heat ratio, investigated in the present study. A comprehensive thermo-economic analysis methodology, presented in this paper, should provide useful guidelines for preliminary sizing and selection of gas turbine cycle for cogeneration applications.
Turbulent Subcooled Boiling Flow—Experiments and Simulations
Authors: Roy R. P. , Kang S. , Zarate J. A. , Laporta A.
Published: July 2002

Experiments and simulations were carried out in this investigation of turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall only was heated. The measurements used, simultaneously, a two-component laser Doppler velocimeter for the liquid velocity field and a fast-response cold-wire for the temperature field, and a dual-sensor fiberoptic probe for the vapor fraction and vapor axial velocity. In the numerical simulation, the two-fluid model equations were solved by the solver ASTRID developed at Electricite´ de France. Wall laws for the liquid phase time-average axial velocity and temperature were developed from the experimental data, and the turbulent Prandtl number in the liquid was determined from the wall laws. The wall laws and turbulent Prandtl number were used in the simulations. The wall heat transfer model utilized the measured turbulent heat flux distribution in the liquid. Results from the simulations were compared with the measurements. Good agreement was found for some of the quantities while the agreement was only fair for others.
Mesh Stiffness Variation Instabilities in Two-Stage Gear Systems
Authors: Lin Jian , Parker Robert G.
Published: July 2002

Mesh stiffness variation, the change in stiffness of meshing teeth as the number of teeth in contact changes, causes parametric instabilities and severe vibration in gear systems. The operating conditions leading to parametric instability are investigated for two-stage gear chains, including idler gear and countershaft configurations. Interactions between the stiffness variations at the two meshes are examined. Primary, secondary, and combination instabilities are studied. The effects of mesh stiffness parameters, including stiffness variation amplitudes, mesh frequencies, contact ratios, and mesh phasing, on these instabilities are analytically identified. For mesh stiffness variation with rectangular waveforms, simple design formulas are derived to control the instability regions by adjusting the contact ratios and mesh phasing. The analytical results are compared to numerical solutions.
Analytical Modeling of the Contact Stress With Nonlinear Gaskets
Authors: Bouzid Abdel-Hakim , Derenne Michel
Published: July 2002

Gasket contact stress and its variation through the gasket width is caused by the rotation of the flange and has an influence on the leakage tightness behavior of bolted flange joints. The future implementation by the ASME of proposed design rules is based on new gasket constants obtained from the ROTT (room temperature tightness) tests conducted on rigid platens. The gasket contact stress distribution needs to be addressed for the purpose of better joint tightness predictions. This paper presents a comprehensive analytical method that predicts the gasket contact stress distribution taking into account the nonlinear mechanical behavior of the gasket material. Based on the flange rotational flexibility, the proposed analytical model that is implemented in the “SuperFlange” program is supported and validated by numerical FEA and experimental analyses on flange rotations, radial distribution of gasket contact stress, and joint leak tightness.
Decision-Based Collaborative Optimization
Authors: Gu Xiaoyu , Renaud John E. , Ashe Leah M. , Batill Stephen M. , Budhiraja Amrjit S. , Krajewski Lee J.
Published: July 2002

In this research a Collaborative Optimization (CO) approach for multidisciplinary systems design is used to develop a decision based design framework for non-deterministic optimization. To date CO strategies have been developed for use in application to deterministic systems design problems. In this research the decision based design (DBD) framework proposed by Hazelrigg [1,2] is modified for use in a collaborative optimization framework. The Hazelrigg framework as originally proposed provides a single level optimization strategy that combines engineering decisions with business decisions in a single level optimization. By transforming this framework for use in collaborative optimization one can decompose the business and engineering decision making processes. In the new multilevel framework of Decision Based Collaborative Optimization (DBCO) the business decisions are made at the system level. These business decisions result in a set of engineering performance targets that disciplinary engineering design teams seek to satisfy as part of subspace optimizations. The Decision Based Collaborative Optimization framework more accurately models the existing relationship between business and engineering in multidisciplinary systems design.
Coordinated Control of Steering and Anti-Roll Bars to Alter Vehicle Rollover Tendencies
Authors: Lee Allan Y.
Published: July 2002

A Variable Dynamic Testbed Vehicle is presently being built for the National Highway Traffic Safety Administration. It will have four-wheel steering, front and rear active antiroll bar systems, four adjustable dampers, and other active controls. Using these active devices, we can alter the vehicle’s understeer coefficient, front/rear load transfer distribution in high-g lateral maneuvers, and roll mode frequency and damping. This study investigates how these active systems could be controlled to alter the vehicle rollover tendencies. In particular, we study how an increased front antiroll bar stiffness, in conjunction with an increased front damper rate and out-of-phase rear steering could improve vehicle rollover resistance and enhance vehicle safety. Similar but “reverse” algorithms could be used to artificially degrade the rollover resistance of a vehicle. Rollover-related accidents could then be studied using such a vehicle. Results obtained could also provide guidelines for the safe operation of the variable dynamic vehicle in limit lateral maneuvers.
Hydrodynamic Design System for Pumps Based on 3-D CAD, CFD, and Inverse Design Method
Authors: Goto Akira , Nohmi Motohiko , Sakurai Takaki , Sogawa Yoshiyasu
Published: July 2002

A computer-aided design system has been developed for hydraulic parts of pumps including impellers, bowl diffusers, volutes, and vaned return channels. The key technologies include three-dimensional (3-D) CAD modeling, automatic grid generation, CFD analysis, and a 3-D inverse design method. The design system is directly connected to a rapid prototyping production system and a flexible manufacturing system composed of a group of DNC machines. The use of this novel design system leads to a drastic reduction of the development time of pumps having high performance, high reliability, and innovative design concepts. The system structure and the design process of “Blade Design System” and “Channel Design System” are presented. Then the design examples are presented briefly based on the previous publications, which included a centrifugal impeller with suppressed secondary flows, a bowl diffuser with suppressed corner separation, a vaned return channel of a multistage pump, and a volute casing. The results of experimental validation, including flow fields measurements, were also presented and discussed briefly.
The Influence of Out-of-Plane Geometry on the Flow Within a Distal End-to-Side Anastomosis
Authors: Sherwin S. J. , Shah O. , Doorly D. J. , Peiro´ J. , Papaharilaou Y. , Watkins N. , Caro C. G. , Dumoulin C. L.
Published: July 2002

This paper describes a computational and experimental investigation of flow in a prototype model geometry of a fully occluded 45 deg distal end-to-side anastomosis. Previous investigations have considered a similar configuration where the centerlines of the bypass and host vessels lie within a plane, thereby producing a plane of symmetry within the flow. We have extended these investigations by deforming the bypass vessel out of the plane of symmetry, thereby breaking the symmetry of the flow and producing a nonplanar geometry. Experimental data were obtained using magnetic resonance imaging of flow within perspex models and computational data were obtained from simulations using a high-order spectral/hp element method. We found that the nonplanar three-dimensional flow notably alters the distribution of wall shear stress at the bed of the anastomosis, reducing the peak wall shear stress peak by approximately 10 percent when compared with the planar model. Furthermore, an increase in the absolute flux of velocity into the occluded region, proximal to the anastomosis, of 80 percent was observed in the nonplanar geometry when compared with the planar geometry. [S0148-0731(00)00401-5]
Instantaneous Flow Rate Measurement of Ideal Gases
Authors: Kawashima Kenji , Kagawa Toshiharu , Fujita Toshinori
Published: July 2002

In this paper, a chamber called an “Isothermal Chamber” was developed. The isothermal chamber can almost realize isothermal condition due to larger heat transfer area and heat transfer coefficient by stuffing steel wool in it. Using this chamber, a simple method to measure flow rates of ideal gases was developed. As the process during charge or discharge is almost isothermal, instantaneous flow rates charged into or discharged from the chamber can be obtained measuring only pressure in the chamber. The steady and the unsteady flow rate of air were measured by the proposed method, and the effectiveness of the method was demonstrated. [S0022-0434(00)00301-4]
The Discharge Flow Ripple of an Axial-Piston Swash-Plate Type Hydrostatic Pump
Authors: Manring Noah D.
Published: July 2002

This research examines the idealized and actual flow-ripple of an axial-piston swash-plate type hydrostatic pump. For the idealized case, a “perfect” pump is examined in which the leakage is considered to be zero and the fluid is considered to be incompressible. Based upon these assumptions, closed-form expressions which describe the characteristics of the idealized flow-ripple are derived. Both the ripple height and the pulse frequency of the ripple are described for a pump with an even and an odd number of pistons. Next, the actual flow-ripple of the pump is examined by considering the pump leakage and the fluid compressibility and for computing these results a numerical program is used. For both the idealized case and the actual case a comparison is made between a nine-piston, an eight-piston, and a seven-piston pump. From the idealized analysis it is quantitatively shown that the eight-piston design is less attractive than the nine or seven-piston design; however, the analysis of the actual pump flow reveals that the qualitative difference between all three designs may not be too significant. From a flow ripple point of view, the numerical results of this research show that a pump designed with an even number of pistons may be as feasible as one that is designed with an odd number of pistons. This is an unexpected conclusion. [S0022-0434(00)00202-1]
Variable Composition Hydrogen/Natural Gas Mixtures for Increased Engine Efficiency and Decreased Emissions
Authors: Sierens R. , Rosseel E.
Published: July 2002

It is well known that adding hydrogen to natural gas extends the lean limit of combustion and that in this way extremely low emission levels can be obtained: even the equivalent zero emission vehicle (EZEV) requirements can be reached. The emissions reduction is especially important at light engine loads. In this paper results are presented for a GM V8 engine. Natural gas, pure hydrogen and different blends of these two fuels have been tested. The fuel supply system used provides natural gas/hydrogen mixtures in variable proportion, regulated independently of the engine operating condition. The influence of the fuel composition on the engine operating characteristics and exhaust emissions has been examined, mainly but not exclusively for 10 and 20 percent hydrogen addition. At least 10 percent hydrogen addition is necessary for a significant improvement in efficiency. Due to the conflicting requirements for low hydrocarbons and low NOx, determining the optimum hythane composition is not straight-forward. For hythane mixtures with a high hydrogen fraction, it is found that a hydrogen content of 80 percent or less guarantees safe engine operation (no backfire nor knock), whatever the air excess factor. It is shown that to obtain maximum engine efficiency for the whole load range while taking low exhaust emissions into account, the mixture composition should be varied with respect to engine load. [S0742-4795(00)02001-9]
Exergy Analysis of Combined Cycles Using Latest Generation Gas Turbines
Authors: Facchini Bruno , Fiaschi Daniele , Manfrida Giampaolo
Published: July 2002

The potential performance of optimized gas-steam combined cycles built around latest-generation gas turbine engines is analyzed, by means of energy/exergy balances. The options here considered are the reheat gas turbine and the H-series with closed-loop steam blade cooling. Simulations of performance were run using a well-tested Modular Code developed at the Department of Energy Engineering of Florence and subsequently improved to include the calculation of exergy destruction of all types (heat transfer, friction, mixing, and chemical irreversibilities). The blade cooling process is analyzed in detail as it is recognized to be of capital importance for performance optimization. The distributions of the relative exergy destruction for the two solutions—both capable of achieving energy/exergy efficiencies in the range of 60 percent—are compared and the potential for improvement is discussed. [S0742-4795(00)00902-9]
Preliminary Economics of Black Liquor Gasifier/Gas Turbine Cogeneration at Pulp and Paper Mills
Authors: Larson Eric D. , Consonni Stefano , Kreutz Thomas G.
Published: July 2002

Black liquor, the lignin-rich byproduct of kraft pulp production, is burned in boiler/steam turbine cogeneration systems at pulp mills today to provide heat and power for onsite use. Black liquor gasification technologies under development would enable this fuel to be used in gas turbines. This paper reports preliminary economics of 100-MWe scale integrated black-liquor gasifier/combined cycles using alternative commercially proposed gasifier designs. The economics are based on detailed full-load performance modeling and on capital, operating and maintenance costs developed in collaboration with engineers at Bechtel Corporation and Stone & Webster Engineering. Comparisons with conventional boiler/steam turbine systems are included. [S0742-4795(00)00402-6]
A PIV Algorithm for Estimating Time-Averaged Velocity Fields
Authors: Meinhart Carl D. , Wereley Steve T. , Santiago Juan G.
Published: July 2002

A PIV algorithm is presented for estimating time-averaged or phase-averaged velocity fields. The algorithm can be applied to situations where signal strength is not sufficient for standard cross correlation techniques, such as a low number of particle images in an interrogation spot, or poor image quality. The algorithm can also be used to increase the spatial resolution of measurements by allowing smaller interrogation spots than those required for standard cross correlation techniques. The quality of the velocity measurements can be dramatically increased by averaging a series of instantaneous correlation functions, before determining the location of the signal peak, as opposed to the commonly used technique of estimating instantaneous velocity fields first and then averaging the velocity fields. The algorithm is applied to a 30μm×300μm microchannel flow. [S0098-2202(00)00602-7]
Film Cooling From Shaped Holes
Authors: Bell C. M. , Hamakawa H. , Ligrani P. M.
Published: July 2002

Local and spatially averaged magnitudes of the adiabatic film cooling effectiveness, the iso-energetic Stanton number ratio, and film cooling performance parameter are measured downstream of (i) cylindrical round, simple angle (CYSA) holes, (ii) laterally diffused, simple angle (LDSA) holes, (iii) laterally diffused, compound angle (LDCA) holes, (iv) forward diffused, simple angle (FDSA) holes, and (v) forward diffused, compound angle (FDCA) holes. Data are presented for length-to-inlet metering diameter ratio of 3, blowing ratios from 0.4 to 1.8, momentum flux ratios from 0.17 to 3.5, and density ratios from 0.9 to 1.4. The LDCA and FDCA arrangements produce higher effectiveness magnitudes over much wider ranges of blowing ratio and momentum flux ratio compared to the three simple angle configurations tested. All three simple angle hole geometries, CYSA, FDSA, and LDSA, show increases of spanwise-averaged adiabatic effectiveness as the density ratio increases from 0.9 to 1.4, which are larger than changes measured downstream of FDCA and LDCA holes. Iso-energetic Stanton number ratios downstream of LDCA and FDCA holes (measured with unity density ratios) are generally increased relative to simple angle geometries for m⩾1.0 when compared at particular normalized streamwise locations, x/D, and blowing ratios, m. Even though this contributes to higher performance parameters and lower protection, overall film cooling performance parameter q˙″/q˙o″ variations with x/D and m are qualitatively similar to variations of adiabatic film cooling effectiveness with x/D and m. Consequently, the best overall protection over the widest ranges of blowing ratios, momentum flux ratios, and streamwise locations is provided by LDCA holes, followed by FDCA holes. Such improvements in protection are partly due to film diffusion from expanded hole shapes, as well as increased lateral spreading of injectant from compound angles. [S0022-1481(00)02202-7]
A Fast and Accurate Method for Numerical Analysis of Elastic Layered Contacts
Authors: Polonsky I. A. , Keer L. M.
Published: July 2002

Solution of contact problems for layered elastic solids generally requires the use of numerical methods. Recently, the fast Fourier transform (FFT) technique has been applied to such contacts. While very fast, FFT is strictly applicable only to periodic contact problems. When it is applied to essentially non-periodic contacts, an error is introduced in the numerical solution. A new method that overcomes the limitation of the “straightforward” FFT approach for solving non-periodic layered contact problems is introduced in the present article. A special correction procedure based on the multi-level multi-summation technique is used to compensate the FFT results for the periodicity error. The use of a robust iteration scheme based on the conjugate gradient method ensures that the new method is applicable to contact problems involving real rough surfaces. Numerical examples demonstrate that the new method is both accurate and fast. [S0742-4787(00)00501-4]
On the Numerical Modeling of High-Speed Hydrodynamic Gas Bearings
Authors: Faria Marco Tulio C. , Andre´s Luis San
Published: July 2002

A numerical study of high-speed hydrodynamic gas bearing performance is presented using both finite element and finite difference methods. Efficient numerical procedures are developed to analyze diffusive-convective thin film gas flows in some simple geometries. A novel direct finite element formulation employing a new class of shape functions is specially devised to solve the Reynolds equation for compressible fluids. The formulation is as computationally efficient as the classical upwind finite element schemes without introducing artificial diffusion into the solution. Bearing load-capacity, static stiffness coefficients and frequency-dependent force coefficients are calculated for gas-lubricated plane and Rayleigh step slider bearings. [S0742-4787(00)01701-X]
A Study on Rolling Element Skew Measurement in a Tapered Roller Bearing With a Specialized Capacitance Probe
Authors: Yang Yeyuan , Danyluk Steven , Hoeprich Michael
Published: July 2002

This paper reports on roller skew in tapered roller bearings. The roller skewing of a tapered roller bearing is experimentally measured with a specialized capacitance probe (Kelvin contact potential difference, CPD, probe). The probe measures the electro-chemical potential difference between the probe and roller surfaces. Two probes are inserted through holes in the housing and bearing outer race. The electrical signals from both ends of a roller are used to determine the skewing. The technique, as well as the effect of lubrication and rotational speed on the roller skewing, is presented. It is shown that the skewing increases with an increase in rotational speed, and the lubrication of the large end of the roller. A theoretical analysis has been developed to account for the experimental results. [S0742-4787(00)01803-8]
Numerical and Experimental Study of Unsteady Flow Field and Vibration in Radial Inflow Turbines
Authors: Kreuz-Ihli T. , Filsinger D. , Schulz A. , Wittig S.
Published: July 2002

The blades of turbocharger impellers are exposed to unsteady aerodynamic forces, which cause blade vibrations and may lead to failures. An indispensable requirement for a safe design of radial inflow turbines is a detailed knowledge of the exciting forces. Up to now, only a few investigations relating to unsteady aerodynamic forces in radial turbines have been presented. To give a detailed insight into the complex phenomena, a comprehensive research project was initiated at the Institut fu¨r Thermische Stro¨mungsmaschinen, at the University of Karlsruhe. A turbocharger test rig was installed in the high-pressure, high-temperature laboratory of the institute. The present paper gives a description of the test rig design and the measuring techniques. The flow field in a vaneless radial inflow turbine was analyzed using laser-Doppler anemometry. First results of unsteady flow field investigations in the turbine scroll and unsteady phase-resolved measurements of the flow field in the turbine rotor will be discussed. Moreover, results from finite element calculations analyzing frequencies and mode shapes are presented. As vibrations in turbines of turbochargers are assumed to be predominantly excited by unsteady aerodynamic forces, a method to predict the actual transient flow in a radial turbine utilizing the commercial Navier–Stokes solver TASCflow3d was developed. Results of the unsteady calculations are presented and comparisons with the measured unsteady flow field are made. As a major result, the excitation effect of the tongue region in a vaneless radial inflow turbine can be demonstrated. [S0889-504X(00)01402-1]
Control of surface reactions in high-performance SiO2 etching
Authors: Tatsumi T. , Matsui M. , Okigawa M. , Sekine M.
Published: July 2002

The relation between SiO2 etch rates and incident fluxes of reactive species in a dual-frequency (27 MHz and 800 kHz) parallel-plate system was evaluated by using various in situ measurements tools. C4F8/Ar/O2 was used for etching gases. The steady-state thickness TC–F of a fluorocarbon polymer layer on the etched SiO2 surface was also measured. The SiO2 etch rate could be related to total F atom flux ΓF-total, which depends on both the incident fluxes of C–F reactive species and the surface reaction probability s. The s is a function of the net energy on the reactive layer (Vnet). This energy is determined by the incident ion energy and the energy loss at the C–F polymer on the etched surface. A change in Vnet from 500 to 1450 V was estimated to correspond to a change in s from 0.01 to 0.1. The steady-state thickness of the C–F polymer TC–F increased when excess C–F species were supplied to the etched surface. A thick polymer (TC–F>1 nm) decreases the ion energy and slows or stops the etching in fine holes. A polymer 5 nm thick can decrease the ion energy by about 750 V. The TC–F must therefore be controlled when high-aspect contact holes are etched.
Electrical properties of thin gate dielectric grown by rapid thermal oxidation
Authors: Lee J. S. , Chang S. J. , Sun S. C. , Jang S. M. , Yu M. C.
Published: July 2002

In this article, we adopted the rapid thermal oxidation (RTO) method to grow gate oxide layers on Si substrates. These RTO oxides were grown in both O2 atmosphere (dry RTO oxide) and in H2 and O2 mixed atmosphere (wet RTO oxide) at above 1000 °C. For comparison, conventional furnace oxides were grown in H2 and O2 mixed atmosphere (furnace wet oxide) as the contrast samples. In this experiment, wet RTO oxides showed better electric characteristics than dry RTO oxides. We also found that a postannealing in nitric oxide (NO) atmosphere can further improve the electric properties of these wet RTO oxides. From these experimental results, we believe that postannealing in NO atmosphere is an effective method to improve oxide electric characteristics. We also found that wet RTO oxide has a superior ability to resist a constant current stress.
Creep–Rupture Properties of C-129Y in Vacuum
Authors: Stephenson R. L.
Published: July 2002

Creep-rupture properties for C-129Y (Nb–10% W–10% Hf–0.1% Y) to 1000 h are presented at 980°, 1095°, and 1205°C. Improvements in strength at 980° and 1205°C can be achieved by pretest annealing at higher temperatures. These improvements are achieved only at the expense of a significant loss in ductility.
Deposition Temperature of Evaporated Permalloy Films
Authors: Bourne Henry C. , Chow L. George , Bartran David S.
Published: July 2002

A vacuum-evaporated Chromel and constantan thin-film thermocouple is developed and used to measure the deposition temperature of evaporated Permalloy films. The maximum Permalloy film temperature is 128°C higher than the glass substrate temperature during deposition for low-evaporation rates (15 Å/sec) due to radiation energy from the tungsten boat and condensation energy from the Permalloy films. In all cases the temperature change due to radiation energy greatly exceeds that due to condensation energy. The heat loss through glass substrate is negligible during deposition; under this condition the temperature change during deposition is predicted by theory.
Effect of Varying Oxidizing and Nitriding Parameters on the Surface of Cr Thin Films
Authors: Alessandrini E. I. , Brusic V.
Published: July 2002

Reflection electron diffraction, electron microscopy, and ellipsometric techniques have been used to study the effect of various oxide and nitride treatments on the surface of chromium films. Thin films of chromium prepared by evaporation and deposited on glass substrates in 10−6-Torr vacuum were oxidized or nitrided for varying times at 50°C intervals in a 400°–600°C temperature range. In this study a correlation between surface structures of the films and the environment in which they were grown could be made. It was found in wet or dry environments that (1) the stable Cr2O3 formed at all times and temperatures during the oxidizing process, (2) two forms of the nitride were observed—the fcc CrN and the hexagonal βCr2N both always in combination with Cr2O3, (3) CrN was detected at a temperature of 450°C, (4) at temperatures above 450°C βCr2N was found and the CrN phase disappeared, (5) an increase in time at all temperatures resulted in grain growth of all compounds. Data obtained for varying conditions were used to estimate the activation energy of oxide and nitride formation on these films. The average values were found to be E = 23 kcal/mole for the oxide and E = 15 kcal/mole for the nitride. In general the oxide and nitride compound formation on the Cr film surfaces followed a parabolic rate law, but the rates were faster than those reported for the bulk.
Interfacial chemistry of the Ba/SiOxNy/Si(100) nanostructure
Authors: Kirsch P. D. , Ekerdt J. G.
Published: July 2002

The interfacial chemistry of a barium/silicon oxynitride (SiOxNy)/silicon nanostructure was investigated with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) to determine if SiOxNy can serve as a barrier for the barium strontium titanate high-k dielectric. The structure consisted of 17 Å of (4 ML) Ba on a 12 Å SiOxNy barrier layer on a Si(100) substrate. Both XPS and SIMS results suggest that barium oxide (BaO) and silicon dioxide (SiO2) at the Ba/SiOxNy interface react to form ∼10 Å of multiphase barium silicate even at 300 K. The kinetics of this reaction were accelerated by annealing the structure in a stepwise fashion to 1000 K. During the annealing, the BaO and SiO2 XPS chemical states attenuate leaving two silicate states. Below the silicate layer, in the oxygen poor region of the nanostructure, ∼10 Å BaSix formed. Annealing the nanostructure to 1000 K for 5 min tested the barrier capabilities of the 12 Å SiOxNy layer. SIMS Ba+, BaSi+, BaSiO+ and Si2N+ signals reveal that Ba containing species do not significantly penetrate below the N≡Si3 bonds characteristic of SiOxNy. Comparison of ∼11 Å SiO2 and ∼12 Å SiOxNy, confirms that the N≡Si3 bonds are the key to the barrier properties. Without N atom incorporation, the Ba+ SIMS signal increased 66% and penetrated ∼24 Å deeper into the Si substrate after a 5 min 600 K anneal.
Three-dimensional rarefied flows in rotating helical channels
Authors: Hwang Young-Kyu , Heo Joong-Sik
Published: July 2002

Numerical simulations of rarefied gas flows in pumping channels of a helical-type drag pump (HTDP) are carried out by using the direct simulation Monte Carlo (DSMC) method. Performance curves obtained by the DSMC method in the slip flow regime are compared with those obtained by the Navier–Stokes equations with slip boundary conditions. Satisfactory agreement between the two results is achieved. Also, the previously developed diffusion model [J. Vac. Sci. Technol. A 13, 2592 (1995)] is modified to predict the performance of a HTDP. Experimental data are presented in the pressure range of 0.02–4 Torr. The numerical results obtained by the modified diffusion model are in good agreement with the experimental data over the entire pressure range from the molecular to the slip flow.
Real-time spectroscopic ellipsometry as a characterization tool for oxide molecular beam epitaxy
Authors: Gibbons B. J. , Hawley M. E. , Trolier-McKinstry S. , Schlom D. G.
Published: July 2002

A real-time spectroscopic ellipsometer (RTSE) was designed and implemented on an oxide molecular beam epitaxy (MBE) system. The RTSE was designed as a complementary tool to the other existing in situ deposition monitors on the MBE. To quantify how the RTSE complemented the other tools (as well as to determine its limitations), the RTSE was used to characterize the deposition of (111)-oriented Y2O3 on (111) Si and (110)-oriented Y2O3 on (100) Si. Results from computer modeling of the RTSE data subsequent to deposition showed excellent agreement with atomic absorption flux measurements, quartz crystal monitor flux measurements, reflection high energy electron diffraction measurements, and Rutherford backscattering spectroscopy. From the RTSE measurements, growth rates and microstructures were determined and verified by ex situ techniques. In addition, the sticking coefficient of yttrium to Y2O3 was found to be 1.00±0.07. Also, the temperature dependent optical properties of the Y2O3 films were measured at 25 and at 730 °C. Nearly bulk values were found, indicating the high quality films deposited via this method.
Absolute sputtering yield of Ti/TiN by Ar+/N+ at 400–700 eV
Authors: Ranjan Rajiv , Allain J. P. , Hendricks M. R. , Ruzic D. N.
Published: July 2002

Ti and TiN films are used as diffusion barrier layers in Al and Cu metallization. They are often produced using physical-vapor-deposition techniques and are subject to energetic particle bombardment during subsequent processes. Therefore, the sputtering yield for ion-induced physical sputtering is important. The absolute sputtering yields of Ti and TiN target materials with 400–700 eV normally incident N and Ar ions are measured here. The experimental values are favorably compared to simulation results from TRIM.SP, which is a vectorized Monte Carlo code simulating ion–surface interaction using a binary collision mode. The phenomenon of reactive sputtering of Ti with incident N is also discussed.
Calibrated scanning spreading resistance microscopy profiling of carriers in III–V structures
Authors: Lu R. P. , Kavanagh K. L. , Dixon-Warren St. J. , Kuhl A. , SpringThorpe A. J. , Griswold E. , Hillier G. , Calder I. , Arés R. , Streater R.
Published: July 2002

Two-dimensional carrier profiling using scanning spreading resistance microscopy (SSRM) has recently been reported for Si- and InP-based structures. In this article, we report SSRM measurements solely on III–V material-based structures. We have studied GaAs and InP doping staircase structures, prepared using molecular-beam epitaxy. These structures were then used as calibration standards for the profiling of carrier density in state-of-the-art III–V-based optoelectronic devices. We discovered that SSRM data on GaAs can be obtained with either polarity; however, only one polarity (positive or negative sample bias for n- or p-GaAs, respectively) produces SSRM results that show quantitative correlation with dopant concentration as determined by secondary ion mass spectrometry (SIMS). In comparison, SSRM measurements using both bias polarities on n-InP correlates well with SIMS, while p-InP exhibits a similar polarity dependence to p-type GaAs. A physical model based on a Schottky junction is proposed to explain these results. We also report calibrated SSRM measurements on GaAs and InP heterojunction bipolar transistor structures.
Comparison of fiber optics and standard nickel catalytic probes for determination of neutral oxygen atoms concentration
Authors: Poberaj Igor , Mozetič Miran , Babič Dušan
Published: July 2002

The density of neutral oxygen atoms in a plasma postglow chamber was measured with a standard Ni catalytic probe and a fiber optical catalytic probe. A highly dissociated oxygen plasma was created in the discharge chamber with an inductively coupled rf generator with a frequency of 27.12 MHz and output power of 200 W. The measurements were performed in the postglow chamber where a movable recombinator for oxygen atoms was placed. The recombinator enabled the adjustment of O density independently of discharge parameters. The density of neutral oxygen atoms was determined at different pressures and different positions of the recombinator. The O density was between 5×1020 and 2×1021 m−3. The fiber probe expressed excellent repeatability as compared to the standard probe. As long as the temperature of the catalyst was above 100 °C both probes gave similar results. At a lower temperature of the standard probe, however, the optical fiber probe gave more reasonable results. The discrepancy was attributed to the decrease of the catalytic activity of nickel at lower temperatures.