bluuebunny/crossref_metadata_2025 huggingface dataset:
Exhaust Emission Deterioration and Combustion Chamber Deposit Composition Over the Life Cycle of Small Utility Engines
Authors: Caceres D. , Reisel J. R. , Sklyarov A. , Poehlman A.
Published: January 2003

In this study, a laboratory test procedure to mimic the life cycle of the small air-cooled engines in field operation is developed. A characterization of exhaust emissions over the life cycle of the engines is achieved with special focus given to the hydrocarbon emissions. Both Briggs and Stratton four-stroke (four-cycle) overhead-valve and side-valve engines with a nominal power output of 3.7 kW (5 hp) are used in this study. Different levels of emissions are observed for each type of engine configuration, and it is noted that the hydrocarbon emissions changed more than CO or NOx emissions. These data support the idea that combustion chamber deposits (CCD) are a significant cause of deteriorating emissions. Chemical analysis techniques are applied to the CCD, and it is found that the deposits consist primarily of polynuclear aromatic compounds and unsaturated hydrocarbons.
Schlieren Observation of Spark-Ignited Premixed Charge Combustion Phenomena Using a Transparent Collimating Cylinder Engine
Authors: Kozuka K. , Ozasa T. , Fujikawa T. , Saito A.
Published: January 2003

The schlieren photographs of in-cylinder processes in a spark-ignited premixed charge gasoline engine were observed via a transparent collimating cylinder and were presented in comparison with a pressure analysis. The schlieren photographs of the spark, the initial flame and the unburned gas ejection from the piston crevice, which is unable to be observed by direct photography, were clearly taken. It shows that the small difference in the initial combustion process among cycles is intensified by the movement of the piston during the expansion stroke. Finally, this difference appears as the cycle by cycle variation in the pressure and the rate of heat release. The observed flame size increased faster and was larger than the burned gas estimated from the pressure. The difference between them is large enough and can not be explained without considering the mixing of burned and unburned gases inside the flame front.
Experimental Study of Aerodynamic and Structural Damping in a Full-Scale Rotating Turbine
Authors: Kielb J. J. , Abhari R. S.
Published: January 2003

Damping in turbomachinery blades has been an important parameter in the study of forced response and high-cycle fatigue, but because of its complexity the sources and physical nature of damping are still not fully understood. This is partly due to the lack of published experimental data and supporting analysis of real rotating components. This paper presents the results of a unique experimental method and data analysis study of multiple damping sources seen in actual turbine components operating at engine conditions. The contributions of both aerodynamic and structural damping for several different blade vibration modes, including bending and torsion, were determined. Results of the experiments indicated that aerodynamic damping was a large component of the total damping for all modes. A study of structural damping as a function of rotational speed was also included to show the effect of friction damping at the blade and disk attachment interface. To the best of the authors’ knowledge, the present paper is the first report of independent and simultaneous structural and aerodynamic damping measurement under engine-level rotational speeds.
Three-Dimensional Finite Element Analysis of Elastic-Plastic Layered Media Under Thermomechanical Surface Loading
Authors: Ye N. , Komvopoulos K.
Published: January 2003

The simultaneous effects of mechanical and thermal surface loadings on the deformation of layered media were analyzed with the finite element method. A three-dimensional model of an elastic sphere sliding over an elastic-plastic layered medium was developed and validated by comparing finite element results with analytical and numerical solutions for the stresses and temperature distribution at the surface of an elastic homogeneous half-space. The evolution of deformation in the layered medium due to thermomechanical surface loading is interpreted in light of the dependence of temperature, von Mises equivalent stress, first principal stress, and equivalent plastic strain on the layer thickness, Peclet number, and sliding distance. The propensity for plastic flow and microcracking in the layered medium is discussed in terms of the thickness and thermal properties of the layer, sliding speed, medium compliance, and normal load. It is shown that frictional shear traction and thermal loading promote stress intensification and plasticity, especially in the case of relatively thin layers exhibiting low thermal conductivity.
Effects of Multistage Coupling and Disk Flexibility on Mistuned Bladed Disk Dynamics
Authors: Bladh R. , Castanier M. P. , Pierre C.
Published: January 2003

The effects of disk flexibility and multistage coupling on the dynamics of bladed disks with and without blade mistuning are investigated. Both free and forced responses are examined using finite element representations of example single and two-stage rotor models. The reported work demonstrates the importance of proper treatment of interstage (stage-to-stage) boundaries in order to yield adequate capture of disk-blade modal interaction in eigenfrequency veering regions. The modified disk-blade modal interactions resulting from interstage-coupling-induced changes in disk flexibility are found to have a significant impact on (a) tuned responses due to excitations passing through eigenfrequency veering regions, and (b) a design’s sensitivity to blade mistuning. Hence, the findings in this paper suggest that multistage analyses may be required when excitations are expected to fall in or near eigenfrequency veering regions or when the sensitivity to blade mistuning is to be accounted for. Conversely, the observed sensitivity to disk flexibility also indicates that the severity of unfavorable structural interblade coupling may be reduced significantly by redesigning the disk(s) and stage-to-stage connectivity. The relatively drastic effects of such modifications illustrated in this work indicate that the design modifications required to alleviate veering-related response problems may be less comprehensive than what might have been expected.
Forced Response of Turbine Engine Bladed Disks and Sensitivity to Harmonic Mistuning
Authors: Kenyon J. A. , Griffin J. H.
Published: January 2003

The mistuned forced response of turbine engine bladed disks is treated using harmonic perturbations in the properties of a continuous ring. A continuous shear spring is attached to the ring in which the stiffness is allowed to vary along the ring annulus. The modes of such a structure with a single harmonic mistuning pattern are shown to obey the Mathieu equation, which is solved to obtain the natural frequencies and modes of the mistuned system. The forced response of the system is then examined to determine the sensitivity of the system to small mistuning. The model is extended to include multiple harmonics, allowing for the possibility of general mistuning. An expression for the maximum amplitude magnification due to small mistuning is developed by showing that high response is caused by distortion of the structural modes. A method to intentionally mistune systems for maximum forced response is demonstrated, and numerical results demonstrate the accuracy of the analytical prediction. The intentionally mistuned system response is shown to be robust with respect to small random mistuning. Such a result might be useful for designing a test rotor for screening new bladed disk designs or for establishing the root cause of fatigue problems.
Optimization of Intentional Mistuning Patterns for the Reduction of the Forced Response Effects of Unintentional Mistuning: Formulation and Assessment
Authors: Choi B.-K. , Lentz J. , Rivas-Guerra A. J. , Mignolet M. P.
Published: January 2003

The focus of the present investigation is on the use of intentional mistuning of bladed disks to reduce their sensitivity to unintentional random mistuning. The class of intentionally mistuned disks considered here is limited, for cost reasons, to arrangements of two types of blades (A and B, say). A two-step procedure is then described to optimize the arrangement of these blades around the disk to reduce the effects of unintentional mistuning. First, a pure optimization effort is undertaken to obtain the pattern(s) of the A and B blades that yields small/the smallest value of the largest amplitude of response to a given excitation in the absence of unintentional mistuning. Then, in the second step, a pattern screening technique based on a recently introduced measure of localization is used to determine which of the patterns does have a large/small sensitivity to random unintentional mistuning. In this manner, expensive Monte Carlo simulations can be eliminated. Examples of application involving both simple bladed disk models and a 17-blade industrial rotor clearly demonstrate the significant benefits of using this class of intentionally mistuned disks.
High-Temperature Fatigue/Creep/Environment Interactions in Compressor Alloys
Authors: Evans W. J. , Jones J. P. , Bache M. R.
Published: January 2003

The high-temperature fatigue response of titanium and nickel alloys destined for high-performance gas turbine applications is considered with particular emphasis given to the role of creep and environmental damage during crack growth. In an attempt to partition the respective contributions from these two rate controlling factors, data are presented for a range of temperature, stress ratio, and pressure conditions. The implications for the extended use of such alloys in future gas turbine designs are discussed.
Development of High-Speed Gas Bearings for High-Power Density Microdevices
Authors: Ehrich F. F. , Jacobson S. A.
Published: January 2003

A 4.2-mm diameter silicon rotor has been operated in a controlled and sustained manner at rotational speeds greater than 1.3 million rpm and power levels approaching 5 W. The rotor, supported by hydrostatic journal and thrust gas bearings, is driven by an air turbine. This turbomachinery/bearing test device was fabricated from single-crystal silicon wafers using micro-fabrication etching and bonding techniques. We believe this device is the first micro-machine to operate at a circumferential tip speed of over 300 meters per second, comparable to conventional macroscale turbomachinery, and necessary for achieving high levels of power density in micro-turbomachinery and micro-electrostatic/ electromagnetic devices. To achieve this level of peripheral speed, micro-fabricated rotors require stable, low-friction bearings for support. Due to the small scale of these devices as well as fabrication constraints that limit the bearing aspect ratio, the design regime is well outside that of more conventional devices. This paper focuses on bearing design and test, and rotordynamic issues for high-speed high-power micro-fabricated devices.
Investigation of Flow in a Steam Turbine Exhaust Hood With/Without Turbine Exit Conditions Simulated
Authors: Liu J. J. , Cui Y. Q. , Jiang H. D.
Published: January 2003

Experimental and numerical investigations for the flow in an exhaust hood model of large steam turbines have been carried out in order to understand the complex three-dimensional flow pattern existing in the hood and also to validate the CFD solver. The model is a typical design for 300/600 MW steam turbines currently in operation. Static pressure at the diffuser tip and hub endwalls and at the hood outer casing is measured and nonuniform circumferential distributions of static pressure are noticed. The velocity field at the model exit is measured and compared with the numerical prediction. The multigrid multiblock three-dimensional Navier-Stokes solver used for the simulations is based upon the TVD Lax-Wendroff scheme and the Baldwin-Lomax turbulence model. Good agreement between numerical results and experimental data is demonstrated. It is found that the flow pattern and hood performance are very different with or without the turbine exit flow conditions simulated.
A High-Efficiency Solid Oxide Fuel Cell Hybrid Power System Using the Mercury 50 Advanced Turbine Systems Gas Turbine
Authors: Lundberg W. L. , Veyo S. E. , Moeckel M. D.
Published: January 2003

The conceptual design of a 20 MWe-class hybrid power generating system that integrates a Siemens Westinghouse pressurized solid oxide fuel cell generator with a Mercury 50 gas turbine is discussed. The Mercury 50 was designed and developed by Caterpillar/Solar Turbines during the U.S. Department of Energy (DOE) Advanced Turbine Systems (ATS) program, and the hybrid system design concept was evaluated during a recently completed project that was part of the DOE high efficiency fossil power plant (HEFPP) program. While achieving a high power system efficiency by the hybrid cycle approach was important, the focus of the design study was to select the solid oxide fuel cell (SOFC) generator capacity such that the low specific cost of the ATS gas turbine and the high efficiency of the more expensive pressurized solid oxide fuel cell (PSOFC) generator would combine optimally to produce an attractively low cost of electricity (COE) for the overall power system. The system cycle and physical characteristics are described; power, efficiency, and emissions estimates are presented; and estimates of system cost and COE are provided. In addition, two bottoming cycle options (steam turbine and ammonia turbine) are described, and performance and cost projections for each are reviewed.
A Thermodynamic Analysis of Tubular Solid Oxide Fuel Cell Based Hybrid Systems
Authors: Rao A. D. , Samuelsen G. S.
Published: January 2003

The goals of a research program recently completed at the University of California, Irvine were to develop analysis strategy for solid oxide fuel cell (SOFC) based systems, to apply the analysis strategy to tubular SOFC hybrid systems and to identify promising hybrid configurations. A pressurized tubular SOFC combined with an intercooled-reheat gas turbine (SureCell™ cycle) is chosen as the base cycle over which improvements are sought. The humid air turbine (HAT) cycle features are incorporated to the base cycle resulting in the SOFC-HAT hybrid cycle which shows an efficiency of 69.05 percent while the base cycle has an efficiency of 66.23 percent. Exergy analysis identified the superior efficiency performance of the SOFC component. Therefore, an additional cycle variation added a second SOFC component followed by a low pressure combustor in place of the reheat combustor of the gas turbine of the SOFC-HAT hybrid. The resulting dual SOFC-HAT hybrid has a thermal efficiency of 75.98 percent. The single SOFC-HAT hybrid gives the lowest cost of electricity (3.54¢/kW-hr) while the dual SOFC-HAT hybrid has the highest cost of electricity (4.02¢/kW-hr) among the three cycles with natural gas priced at $3/GJ. The dual SOFC-HAT hybrid plant cost is calculated to be significantly higher because the fraction of power produced by the SOFC(s) is significantly higher than that in the other cases on the basis of $1100/kw initial cost for the SOFC. The dual SOFC-HAT hybrid can only be justified in favor of the single SOFC-HAT hybrid when the price of natural gas is greater than $14/GJ or if a severe carbon tax on the order of $180/ton of CO2 is imposed while natural gas price remains at $3/GJ.
Selecting and Developing Advanced Alloys for Creep-Resistance for Microturbine Recuperator Applications1
Authors: Maziasz P. J. , Swindeman R. W.
Published: January 2003

Recuperators are considered essential hardware to achieve the efficiencies desired for advanced microturbines. Compact recuperator technologies, including primary surface, plate and fin, and spiral, all require thin section materials that have high-temperature strength and corrosion resistance up to 750°C or above, and yet remain as low cost as possible. The effects of processing and microstructure on creep-rupture resistance at 750°C and 100 MPa were determined for a range of austenitic stainless alloys made into 0.1-mm foils. Two groups of alloys were identified with regard to improved creep resistance relative to type 347 stainless steel. Alloys with better creep-rupture resistance included alloys 120, 230, modified 803 and alloy 740 (formerly thermie-alloy), while alloy 214 and 625 exhibited much better creep strength. Alloys 120 and modified 803 appeared to have the most cost-effective improvements in creep strength relative to type 347 stainless steel, and should be attractive for advanced microturbine recuperator applications.
Model Identification of a Rotor With Magnetic Bearings
Authors: Va´zquez J. A. , Maslen E. H. , Ahn H.-J. , Han D.-C.
Published: January 2003

The experimental identification of a long flexible rotor with three magnetic bearing journals is presented. Frequency response functions are measured between the magnetic bearing journals and the sensor locations while the rotor is suspended horizontally with piano wire. These frequency response functions are compared with the responses of a rotor model and a reconciliation process is used to reduce the discrepancies between the model and the measured data. In this identification, the wire and the fit of the magnetic bearing journals are identified as the sources of model error. As a result of the reconciliation process, equivalent dynamic stiffness are calculated for the piano wire and the fit of the magnetic bearing journals. Several significant numeral issues that were encountered during the process are discussed and solutions to some of these problems are presented.
Dynamic Modeling and Validation of a Lorentz, Self-Bearing Motor Test Rig
Authors: Stephens L. S. , Kim D.-G.
Published: January 2003

A new type of self-bearing motor that uses Lorentz-type forces to generate both bearing force and motoring torque has been developed. The motor stator is of slotless construction with four three-phase windings. The motor rotor is constructed of 16 surface mounted permanent magnets (PM’s). The main advantage of the design is that it eliminates the tradeoff between motoring torque and bearing force with PM thickness as found in previous designs. This paper presents the dynamic model for the self-bearing motor and illustrates how the model is integrated into the overall system model of the motor test rig. The dynamic model is validated against experimentally measured transfer functions with good agreement between the two.
The Effect of Adding Oxygenated Compounds to Gasoline on Automotive Exhaust Emissions
Authors: Poulopoulos S. G. , Philippopoulos C. J.
Published: January 2003

In the present work, the effect of adding ethanol or methyl tertiary butyl ether (MTBE) to gasoline on the regulated and unregulated emissions from an internal combustion engine with a typical three-way catalyst was studied. The addition of ethanol to fuel (10% w/w) increased both the research octane number and the Reid vapor pressure of the fuel, whereas adding 11% w/w MTBE caused an increase only in the research octane number of the fuel. When the fuel contained MTBE, less hydrocarbons, carbon monoxide, and acetaldehyde were emitted in the tailpipe. The increased emissions of acetaldehyde and ethanol were the main disadvantages of using ethanol.
Experimental and Theoretical Optimization of Combustion Chamber and Fuel Distribution for the Low Emission Direct-Injection Diesel Engine
Authors: Kidoguchi Y. , Sanda M. , Miwa K.
Published: January 2003

Effects of combustion chamber geometry and initial mixture distribution on the combustion process were investigated in a direct-injection diesel engine. In the engine experiment, a high squish combustion chamber with a squish lip could reduce both NOx and particulate emissions with retarded injection timing. According to the results of CFD computation and phenomenological modeling, the high squish combustion chamber with a central pip is effective to keep the combusting mixture under the squish lip until the end of combustion and the combustion region forms rich and highly turbulent atmosphere. This kind of mixture distribution tends to reduce initial burning, resulting in restraint of NOx emission while keeping low particulate emission.
Effect of Surface Patterning on Contact Deformation of Elastic-Plastic Layered Media
Authors: Gong Z.-Q. , Komvopoulos K.
Published: January 2003

A plane-strain finite element analysis for patterned elastic-plastic layered media was performed in order to elucidate the effect of surface geometry on the deformation and stress fields due to normal and sliding contact. Surface interaction between the layered media and a rigid asperity was modeled with special contact elements. Results for the contact pressure distribution, surface tensile stress, and subsurface equivalent plastic strain are presented for layered media with different meandered and sinusoidal surfaces. The significance of surface patterning on the deformation behavior is interpreted in terms of stress and strain results illustrative of the tendency for crack initiation and plastic deformation in the first two layers, where deformation is confined in all simulation cases. Relations for the contact pressure concentration factor and onset of yielding in the first (hard) layer are derived from finite element results for indented layered media with sinusoidal surface patterns. Predictions for the indentation depth at the onset of yielding based on the developed yield criterion are shown to be in good agreement with those obtained from finite element simulations.
Transient Thermoelastic Stress Fields in a Half-Space
Authors: Liu Shuangbiao , Wang Qian
Published: January 2003

Computing the thermoelastic stress field of a material subjected to frictional heating is essential for component failure prevention and life prediction. However, the analysis for three-dimensional thermoelastic stress field for tribological problems is not well developed. Furthermore, the pressure distribution due to rough surface contact is irregular; hence the frictional heating can hardly be described by an analytical expression. This paper presents a novel set of frequency-domain expressions (frequency response functions) of the thermoelastic stress field of a uniformly moving three-dimensional elastic half-space subjected to arbitrary transient frictional heating, where the velocity of the half-space, its magnitude and direction, can be an arbitrary function of time. General formulas are expressed in the form of time integrals, and important expressions for constant velocities are given for the transient-instantaneous, transient-continuous, and steady-state cases. The thermoelastic stress field inside a translating half-space with constant velocities are illustrated and discussed by using the discrete convolution and fast Fourier transform method when a parabolic type or an irregularly distributed heat source is applied.
Combustion Test Results of an Uncooled Combustor With Ceramic Matrix Composite Liner
Authors: Suzuki Y. , Satoh T. , Kawano M. , Akikawa N. , Matsuda Y.
Published: January 2003

A reverse-flow annular combustor with its casing diameter of 400 mm was developed using an uncooled liner made of a three-dimensional woven ceramic matrix composite. The combustor was tested using the TRDI high-pressure combustor test facility at the combustor maximum inlet and exit temperature of 723 K and 1623 K, respectively. Although both the material and combustion characteristics were evaluated in the test, this report focused on the combustion performance. As the results of the test, the high combustion efficiency and high heat release ratio of 99.9% and 1032 W/m3/Pa were obtained at the design point. The latter figure is approximately twice as high as that of existing reverse-flow annular combustors. Pattern factor was sufficiently low and was less than 0.1. Surface temperatures of the liner wall were confirmed to be higher than the limit of the combustor made of existing heat-resistant metallic materials.
The Generalized Newtonian Fluid Model and Elastohydrodynamic Film Thickness
Authors: Bair Scott , Qureshi Farrukh
Published: January 2003

The nature of real shear-thinning in elastohydrodynamic contacts is well-known from both experimental measurement and nonequilibrium molecular dynamics to follow a power-law. Shear-thinning will affect the film thickness when the Newtonian limit is low enough to occur in the inlet zone (less than about 1 MPa shear stress). Then kinetic theory tells us that film thinning should occur for molecular weight greater than 2000 kg/kmol. We present a review of generalized Newtonian models, flow curves for real lubricants and comparison of calculated and measured film thickness. The calculations utilize measurable liquid behavior, in contrast to most previous work.
A Comprehensive Study of Self-Induced Torque Amplification in Rotary Viscous Couplings
Authors: Mohan Sankar K. , Ramarao Bandaru V.
Published: January 2003

Rotary viscous couplings with interleaved, perforated plates and viscous fluids are used in automotive systems to transmit torque. During operation, viscous dissipation raises fluid temperature, lowers fluid viscosity and causes the torque transmitted to drop monotonically to unusable levels. Couplings designed with certain plate geometry exhibit a reversal of the torque trend with temperature, and transmit increasingly high torque even under continuous operation. Such couplings achieve torque amplification factors in excess of twenty, compared to earlier couplings. This torque amplification phenomenon has been utilized by industry without fully understanding the mechanisms involved. A comprehensive theory is proposed to explain the complex sequence of events that results in this “anomalous,” but useful phenomenon. Mathematical models are developed for each interdependent process. A visual simulation tool is used to model the intricate dynamics inside the coupling. Results from the simulation model are compared with experimental findings. The various thermodynamic, hydrodynamic, structural and mechanical processes are delineated and tested with a combination of theoretical analysis, computational simulation and experimental observations. The proposed theory identifies, defines and explains the conditions necessary for initiating and sustaining the self-induced torque amplification. The hypotheses are validated by the reasonable agreement of the model with the test results.
Some Studies on Scuffing Performance of Surface Treated AISI 4340 Steels
Authors: Ramprasad M. , Mayuram M. M.
Published: January 2003

Scuffing or scoring is an important form of damage leading to component replacements in lubricated mechanical systems such as power drives, gears, bearings, cams and followers, piston rings etc. Since scuffing necessarily involves localized welding of asperities, suitable surface modifications or coating can impart a good resistance to scuffing. A new class of low temperature salt bath nitriding process provides good resistance to scuffing. The current work is on evaluation of the scuffing resistance of AISI 4340 steels imparted with two such treatments. Experimental investigations were conducted on Sursulf and Arcor treated AISI 4340 steel specimen using a pin on ring test system under boundary lubrication condition. Continuous monitoring of friction records and (near surface) bulk temperature were done under step loading. Limiting loads and load velocity relations were evaluated and using the data generated and a thermo-mechanical wear model, performance is indexed. Off line studies on surface finish, hardness variations and surface transformations were also accomplished. Some salient aspects of the investigation and data generated are presented here. Onset of scuffing was observed to be far delayed with pin specimen imparted with these treatments compared to hardening.
Stability Analysis of a Rotating System Due to the Effect of Ball Bearing Waviness
Authors: Jang G. H. , Jeong S. W.
Published: January 2003

This research presents an analytical model to investigate the stability due to the ball bearing waviness in a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu’s equation, because the stiffness coefficients have time-varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill’s infinite determinant for these algebraic equations. The validity of this research is proven by comparing the stability chart with the time responses of the vibration model suggested by prior research. This research shows that the waviness in the ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 i=1,2,3,….
Adjoint Design Sensitivity Analysis of Molecular Gas Film Lubrication Sliders
Authors: Yoon Sang-Joon , Choi Dong-Hoon
Published: January 2003

This paper proposes an analytical design sensitivity analysis (DSA) to topological parameters of MGL (molecular gas film lubrication) sliders by introducing an adjoint variable method. For the analysis of slider air bearings, we used the spatial discretization of the generalized lubrication equation based on a control volume formulation. The residual functions for inverse analysis of the slider are considered as the equality constraint functions. The slider rail heights of all grid cells are chosen as design variables since they are the topological parameters determining air bearing surface (ABS). Then, a complicated adjoint variable equation is formulated to directly handle the highly nonlinear asymmetric coefficient matrix and vector in the discrete system equations of slider air bearings. An alternating direction implicit (ADI) scheme is utilized to efficiently solve large-scale problem in special band storage. The simulation results of DSA are directly compared with those of finite-difference approximation (FDA) to show the effectiveness and accuracy of the proposed approach. The overall sensitivity distribution over the ABS is reported, and clearly shows to which section of the ABS the special attention should be given during the manufacturing process. It is demonstrated that the proposed method can reduce more than 99 percent of the CPU time in comparison with FDA, even though both methods give the same results.
The Evolution of Geometry for a Wearing Circular Cam: Analytical and Computer Simulation With Comparison to Experiment
Authors: Dickrell D. J. , Dooner D. B. , Sawyer W. G.
Published: January 2003

The evolution of the geometry of a simple two-dimensional circular cam as a result of wear is studied using three complementary approaches: a closed form analytical expression, a computer simulation, and the development of an experimental apparatus. Experiments were run for over 1.5 million cycles, and measurements of cam shape and follower motion were recorded and compared favorably to the predictions of both techniques. Errors associated with an accelerated computational approach are discussed.
In Vitro Measurement of the Restraining Role of the Anterior Cruciate Ligament During Walking and Stair Ascent
Authors: Ahmed A. M. , McLean C.
Published: January 2003

The study aimed to test the hypothesis that the restraining role of the anterior cruciate ligament (ACL) of the knee is significant during the activities of normal walking and stair ascent. The role of the ACL was determined from the effect of ACL excision on tibiofemoral displacement patterns measured in vitro for fresh-frozen knee specimens subjected to simulated knee kinetics of walking (n=12) and stair ascent (n=7). The knee kinetics were simulated using a newly developed dynamic simulator able to replicate the sagittal-plane knee kinetics with reasonable accuracy while ensuring unconstrained tibiofemoral kinematics. The displacements were measured using a calibrated six degree-of-freedom electromechanical goniometer. For the simulation of the walking cycle, two types of knee flexion/extension moment patterns were used: the more common “biphasic” pattern, and an extensor muscle force intensive pattern. For both of these patterns, the restraining role of the ACL to tibial anterior translation was found to be significant throughout the stance phase and in the terminal swing phase, when the knee angle was in the range of 4° to 30°. The effect of ACL excision was an increase in tibial anterior translation by 4 mm to 5 mm. For the stair ascent cycle, however, the restraining role of the ACL was significant only during the terminal stance phase, and not during the initial and middle segments of the phase. Although, in these segments, the knee moments were comparable to that in walking, the knee angle was in the range of 60° to 70°. These results have been shown to be consistent with available data on knee mechanics and ACL function measured under static loading conditions.
Adhesion and Pull-Off Forces for Polysilicon MEMS Surfaces Using the Sub-Boundary Lubrication Model
Authors: Suh Allison Y. , Polycarpou Andreas A.
Published: January 2003

Miniature devices including MEMS and the head disk interface in magnetic storage often include very smooth surfaces, typically having root-mean-square roughness, σ of the order of 10 nm or less. When such smooth surfaces contact, or come into proximity of each other, either in dry or wet environments, then strong intermolecular (adhesive) forces may arise. Such strong intermolecular forces may result in unacceptable and possibly catastrophic adhesion, stiction, friction and wear. In the present paper, a model termed sub-boundary lubrication (SBL) adhesion model is used to calculate the adhesion forces, and an elastic-plastic model is used to calculate the contact forces at typical MEMS interfaces. Several levels of surface roughness are investigated representing polished and as-deposited polysilicon films that are typically found in MEMS. The SBL adhesion model reveals the significance of the surface roughness on the adhesion and pull-off forces as the surfaces become smoother. The validity of using the SBL adhesion model to estimate the pull-off forces in miniature systems is further supported by direct comparison with experimental pull-off force measurements performed on silicon and gold interfaces. Finally, the significance of the interfacial forces as relate to the reliability of MEMS interfaces is discussed.
A New Finite-Element Based Suspension Model Including Displacement Limiters for Load/Unload Simulations
Authors: Weissner Stefan , Zander Uwe , Talke Frank E.
Published: January 2003

A new beam suspension model for load/unload simulations of magnetic hard disk drive sliders is presented. The model is applicable to the load/unload process as well as to the dynamic flying behavior of the slider on the disk. Suspension and gimbal are modeled with C1 continuous beam elements. The roll degree of freedom of the slider is decoupled from spacing and pitch. The numerical implementation of the model is described. Loading and unloading of a typical subambient pressure type slider is presented.
Hot Spotting and Judder Phenomena in Aluminum Drum Brakes
Authors: Lee Kwangjin , Brooks, Frank W.
Published: January 2003

Hot spotting and judder phenomena were observed in automotive aluminum drum brakes. A vehicle judder test schedule was developed to determine the critical speed for thermoelastic instability (TEI). The brake material properties relevant to the TEI analysis were measured as a function of temperature. The critical speeds for the brake systems with different drum materials were determined by the judder schedule and they are compared with the analytical predictions of Lee (2000). The brake drums and linings were then modified and tested in order to investigate its effects on the hot spotting and judder propensity. The design modifications include brake linings with a different compound, stress-relieved drums, linings with a convex or concave surface finish, three-segmented linings, and linings with a circumferential groove. The linings with a circumferencial groove effectively reduce the size of hot spots and the best judder rating was achieved.
Elastohydrodynamics and Mechanics of Rectangular Elastomeric Seals for Reciprocating Piston Rods
Authors: Nikas George K.
Published: January 2003

A numerical model was developed to study the sealing performance of rectangular elastomeric seals for reciprocating piston rods used in linear hydraulic actuators. The model takes into account a large number of parameters and has been applied in the study of seals for aircraft actuation assemblies in a broad range of temperatures (−55°C to +135°C) and sealed pressures (1–50 MPa or more). The model is used to calculate the contact pressures and film thickness maps as well as the leakage rates and friction for the dynamic or static contact between a seal and a reciprocating piston rod, aiming at the minimization of both the leakage and the wear of the seals.
Stokes Flow in Thin Films
Authors: van Odyck D. E. A. , Venner C. H.
Published: January 2003

Present understanding of the mechanisms of lubrication and the load carrying capacity of lubricant films mainly relies on models in which the Reynolds equation is used to describe the flow. The narrow gap assumption is a key element in its derivation from the Navier Stokes equations. However, the tendency in applications is that lubricated contacts have to operate at smaller film thickness levels, and because engineering surfaces are never perfectly smooth, locally in the film this narrow gap assumption may violated. In addition to this geometric limitation of the validity of the Reynolds equation may come a piezoviscous and compressibility related limitation. In this paper the accuracy of the predictions of the Reynolds model in relation to the local geometry of the gap is investigated. A numerical solution algorithm for the flow in a narrow gap has been developed based on the Stokes equations. For a model problem the differences between the pressure and velocity fields according to the Stokes model and the Reynolds equation have been investigated. The configuration entails a lower flat surface together with an upper surface (flat or parabolic) in which a local defect (single asperity) of known geometry has been embedded. It is investigated how the magnitude of the differences develops as a function of the geometric parameters of the film and the feature. Finally, it is discussed to what extend for these problems a perturbation approach can provide accurate corrections to be applied to the Reynolds solution.
Reynolds Equation for Spherical Bearings
Authors: Meyer Donna
Published: January 2003

Osborne Reynolds’ classical paper on the theory of lubrication Reynolds (1886) produced the generalized Reynolds equation. For spherical bearing applications, the generalized Reynolds equation is transformed in order to obtain useful results when the hemispherical shell is not in a horizontal position. A new film thickness expression is also presented. These transformations permit the determination of pressure distributions and fluid film thickness for any orientation of the hemispherical shell including the horizontal position, for which the conventional description of Reynolds equation is well suited. The resulting equation in two-dimensional form, for an incompressible, variable viscosity fluid, with upper and lower sliding surfaces, in spherical coordinates, contains the inclination angle β, which accounts for non-horizontal positions of the shell.
Quantitative Comparisons Between Measured and Solved EHL Dimples in Point Contacts
Authors: Yang P. , Kaneta and M. , Masuda S.
Published: January 2003

Using a mineral bright stock oil as lubricant, the dimple phenomena in the circular EHL contacts composed of a glass disk and a steel ball were investigated experimentally with the optical interferometry technique. The traction coefficient was also measured. The experimental results were compared quantitatively with the numerical results of the corresponding thermal Newtonian EHL solutions. The comparisons show that the Newtonian thermal EHL theory can explain very well the relationship between the dimple phenomena and the slide-roll ratio, but cannot predict accurately the depth of the dimple and the magnitude of the traction coefficient. It has also been found that the Newtonian flow model overestimates the effect of the temperature-viscosity wedge and consequently, a non-Newtonian flow model may be necessary for a better understanding of the EHL dimple phenomena.
Dynamic Contact of a Rigid Sphere With an Elastic Half-Space: A Numerical Simulation
Authors: Streator Jeffrey L.
Published: January 2003

A numerical simulation is performed to investigate the development of forces between a rigid sphere and an elastic half-space during normal, dynamic contact in the absence of friction. Of interest is to quantify the magnitude of forces that arise and to identify any sources of hysteresis between approach and separation, the latter being associated with energy dissipation. In the simulation a rigid sphere approaches and separates from an isotropic, linearly elastic half-space at a prescribed, constant speed. Surface forces are incorporated in the model by ascribing a surface interaction potential derived from the Lennard-Jones 6-12 intermolecular potential. Dynamical equations of motion for the interface are integrated numerically during the approach-separation event. During the approach phase, it is found that the magnitude of adhesive force is generally consistent with well-known static-equilibrium based analytical models (e.g., DMT and JKR), depending upon the strength of the interaction potential. However, during separation, the attractive force computed in this dynamic simulation may be several times higher than the predictions of the analytical models. Additionally, the maximum compressive forces attained during the contact process far exceed the predictions of Hertzian contact theory. The discrepancy between results of this simulation and those of the static-equilibrium analytical and numerical models indicate that dynamic interactions play a significant role in determining the development of contact forces. Moreover, dynamic effects persist even when the approach-separation speed of the sphere is small compared to the dilatation and shear wave speeds of the half-space.
Self-Similarity in Abrasiveness of Hard Carbon-Containing Coatings
Authors: Borodich Feodor M. , Keer Leon M. , Harris Stephen J.
Published: January 2003

The abrasiveness of hard carbon-containing thin films such as diamond-like carbon (DLC) and boron carbide (nominally B4C) towards steel is considered here. First, a remarkably simple experimentally observed power-law relationship between the abrasion rate of the coatings and the number of cycles is described. This relationship remains valid over at least 4 orders of magnitude of the number of cycles, with very little experimental scatter. Then possible models of wear are discussed. It is assumed that the dominant mechanism of steel wear is its mechanical abrasion by nano-scale asperities on the coating that have relatively large attack angles, i.e. by the so-called sharp asperities. Wear of coating is assumed to be mainly due to physical/chemical processes. Finally, models of the abrasion process for two basic cases are presented, namely a coated ball on a flat steel disk and a steel ball on a coated flat disk. The nominal contact region can be considered as constant in the former case, while in the latter case, the size of the region may be enlarged due to wear of the steel. These models of the abrasion process are based on the assumption of self-similar changes of the distribution function characterizing the statistical properties of patterns of scattered surface sharp asperities. It is shown that the power-law relationship for abrasion rate follows from the models.
Analysis of Tracking Characteristics and Optimum Design of Tri-Pad Slider to Micro-Waviness
Authors: Yamane Masami , Ono Kyosuke , Iida Kohei
Published: January 2003

This paper describes optimum air-bearing design of a tri-pad slider in terms of tracking ability to micro-waviness based on theoretical analysis of the two-degree-of-freedom slider model and the distributed and concentrated air-bearing stiffness model. Although a short tri-pad type slider was introduced through the load/unload technique, we point out that this type of slider is superior to the traditional rail type slider in terms of tracking ability to micro-waviness. More importantly, the distance between head-gap position and the rear air-bearing center should be made as small as possible. The spacing variation due to lower mode resonance can be eliminated if the positions of front and rear air-bearing centers are located at the center of percussion. The resonance amplitude of the higher order mode in spacing variation can be reduced if the length of the rear air-bearing pad is designed to be 1.2∼1.3 times the wavelength of the higher mode resonance frequency. Since the momental stiffness of the front air-bearing prevents the head-gap from tracking micro-waviness, the front air-bearing length should be made short or the ratio of rear to front air-bearing stiffness should be made large. If the resonance amplitude of the lower mode must be decreased, the front air-bearing length should be designed to be 1.2∼1.3 times the wavelength of the lower mode resonance frequency.
The Axial Injury Tolerance of the Human Foot/Ankle Complex and the Effect of Achilles Tension
Authors: Funk James R. , Crandall Jeff R. , Tourret Lisa J. , MacMahon Conor B. , Bass Cameron R. , Patrie James T. , Khaewpong Nopporn , Eppinger Rolf H.
Published: January 2003

Axial loading of the foot/ankle complex is an important injury mechanism in vehicular trauma that is responsible for severe injuries such as calcaneal and tibial pilon fractures. Axial loading may be applied to the leg externally, by the toepan and/or pedals, as well as internally, by active muscle tension applied through the Achilles tendon during pre-impact bracing. The objectives of this study were to investigate the effect of Achilles tension on fracture mode and to empirically model the axial loading tolerance of the foot/ankle complex. Blunt axial impact tests were performed on forty-three (43) isolated lower extremities with and without experimentally simulated Achilles tension. The primary fracture mode was calcaneal fracture in both groups. However, fracture initiated at the distal tibia more frequently with the addition of Achilles tension p<0.05. Acoustic sensors mounted to the bone demonstrated that fracture initiated at the time of peak local axial force. A survival analysis was performed on the injury data set using a Weibull regression model with specimen age, gender, body mass, and peak Achilles tension as predictor variables R2=0.90. A closed-form survivor function was developed to predict the risk of fracture to the foot/ankle complex in terms of axial tibial force. The axial tibial force associated with a 50% risk of injury ranged from 3.7 kN for a 65 year-old 5th percentile female to 8.3 kN for a 45 year-old 50th percentile male, assuming no Achilles tension. The survivor function presented here may be used to estimate the risk of foot/ankle fracture that a blunt axial impact would pose to a human based on the peak tibial axial force measured by an anthropomorphic test device.