bluuebunny/crossref_metadata_2025 huggingface dataset:
Autonomous Vibration Suppression Using On-Line Pole-Zero Identification
Authors: McEver Mark , Leo Donald J.
Published: July 2002

An on-line identification and control algorithm is developed based on the properties of collocated sensing and actuation. The feedback control law consists of second-order compensators that achieve equivalent damping in both the filter dynamics and resonant structural dynamics, thus maximizing the damping in the structure and controller. Optimal design of the feedback compensator is obtained using a pole placement algorithm applied to a single, undamped resonant mode. Numerical analysis indicates that multiple modes and structural damping do not appreciably change the damping achieved using the optimal parameters. The pole placement analysis demonstrates that only the pole-zero spacing and DC gain of the collocated transfer function are required to choose the optimal parameters. An on-line identification procedure is developed that sequentially determines the DC gain and pole-zero spacing and automatically designs the feedback compensator. This forms the basis for the autonomous control algorithm. Experimental results on a flexible beam demonstrate that the procedure can accurately identify the pole-zero spacing and automatically design the feedback compensator. A fivefold increase in damping is achieved in the first mode and a twofold increase in damping is achieved in the second mode. Discrepancies between predicted and measured damping are attributed to phase lags due to signal conditioning and low-pass filtering of the sensor signal.
The Control Torque on the Swash Plate of an Axial-Piston Pump Utilizing Piston-Bore Springs
Authors: Manring Noah D. , Damtew Fikreadam A.
Published: July 2002

This research begins by presenting a nontraditional pump design which utilizes a piston-bore spring. The piston-bore spring is included in this design for the purpose of holding the cylinder block against the valve plate and for forcing the pistons in the negative x-direction. By forcing the pistons in this direction, the piston-bore spring also assists in holding the slippers against the swash plate during the normal operation of the pump. Though these advantages of the design may be readily seen by inspection, it is not obvious how the control torque on the swash plate is effected by the piston-bore spring nor is it obvious how one would go about designing the spring to produce a favorable result. To clarify the benefit of this design, a mechanical analysis is conducted to describe the effect of the spring on the control torque itself. As a result of this analysis, a general equation which describes the swash-plate motion is presented. Within this equation, it may be seen that the spring force provides a restoring force on the swash plate which tends to stabilize the design. The piston-bore spring is also shown to be capable of eliminating the cross-over from a stroke increasing swash-plate torque to a stroke decreasing swash-plate torque. By eliminating this cross over, the backlash in the pump control (which is commonly observed in practice) can be prevented.
On Plastic Collapse of Media With Random Yield Strength
Authors: Ku A. P.-D. , Nordgren R. P.
Published: July 2002

This paper concerns the plastic collapse of an elastic/perfectly plastic medium with randomly variable yield strength under a fixed load. The yield strength is represented by a Gaussian random field of known statistical properties. Using the theorems of limit analysis and the methods of reliability theory, algorithms are developed for the computation of upper and lower bounds on the probability of plastic collapse. By varying the magnitude of the fixed load, bounds on the probability distribution function for the collapse load can be computed. Results are given for uniform pressure applied to a rectangular region of the surface of an elastic/plastic half-space. For the corresponding plane problem, results for the classical Hill and Prandtl failure mechanisms are compared. Three-dimensional results are found to differ significantly from those of the plane problem. Comparison is made with results of a previous approximate method for three-dimensional problems.
Foundations of Buoyancy Driven Heat Transfer Correlations
Authors: Arpacı Vedat S. , Kao Shu-Hsin
Published: July 2002

In terms of a dimensionless number, ΠN∼Ra/1+Pr−1, introduced by Arpacı (1986, 1990, 1995) for buoyancy driven flows, Ra and Pr respectively being the usual Rayleigh and Prandtl numbers, two well-known correlations (Churchill and Chu, 1975) for natural convection next to a vertical isothermal plate are reduced in terms of ΠL=Ra/1+0.492Pr−1 to Nu=0.67ΠL1/4,103⩽ΠL⩽109, for the laminar case, and in terms of ΠT=Ra/1+0.164Pr−1 to Nu=0.15ΠT1/3,109⩽ΠT⩽1012, for the turbulent case.
Optimum Process Design in Sheet-Metal Forming With Finite Element Analysis
Authors: Huh Hoon , Kim Se-Ho
Published: July 2002

Process optimization is carried out to determine process parameters which satisfy the given design requirements and constraint conditions in sheet-metal forming processes. The scheme incorporates with a rigid-plastic finite element method for calculation of the final shape and the strain distribution. The optimization scheme adopts a direct differentiation method or a response surface methodology in order to seek for the optimum condition of process parameters. The algorithm developed is applied to design of the draw-bead force and the die shapes in deep drawing processes. Results show that design of process parameters is well performed to increase the amount of strain for increasing the strength or to decrease the amount of strain for preventing fracture by tearing. The present algorithm also enhances the stable optimum solution with small number of iterations for optimization.
Theory Versus Experiment for the Rotordynamic Impedances of Two Hole-Pattern-Stator Gas Annular Seals
Authors: Holt Christopher G. , Childs Dara W.
Published: July 2002

Measured rotordynamic impedances are presented for two hole-pattern-stator seals and one smooth bore seal. These measured results are compared to predictions from a two-control-volume model and realized in the code ISOTSEAL (constant-temperature seal code). The hole-pattern seals have cell depths of 2.03 mm and 3.18 mm with a cell diameter of 1.59 mm. The hole-area density factor for both hole-pattern seals is 43 percent. The seal diameter is 114.71 mm with an L/D ratio of 0.75. Measured results for radial impedances and leakage were obtained. Test conditions involved three speeds out to 20,200 rpm, three inlet pressures out to 17.2 bar, and two exit-to-inlet pressure ratios of 40 percent and 54 percent. As predicted, the hole-pattern seals exhibit frequency-dependent rotordynamic coefficients K(Ω), k(Ω), C(Ω), c(Ω). Results of the tests show that the 3.18 mm hole-pattern seal has the highest average effective stiffness and lowest effective damping. Direct and effective stiffness were under-predicted in all cases; however, measured direct and effective damping are reasonably well predicted. Impedance predictions improve with increasing pressure ratio. Comparisons of leakage correlate extremely well with predictions; worse case deviations never exceed 10 percent. Results show that leakage decreases as cell depth increases. Results also show that the exit temperature increases substantially with increasing rotational speed.
Effects of Misalignment on Turbulent Flow Hybrid Thrust Bearings
Authors: San Andre´s Luis
Published: July 2002

An extended computational bulk-flow analysis for prediction of performance in angled injection, orifice-compensated hydrostatic/hydrodynamic thrust bearings is presented. The fluid motion within the thin film lands is governed by mass conservation and momentum transport equations. Mass flow conservation and a simple model for momentum transport within the hydrostatic bearing recesses are also accounted for. A perturbation analysis for small amplitude shaft axial motions and angulations leads to zeroth and first-order equations describing the equilibrium and perturbed fluid flows. The computational procedure predicts the bearing flow rate, thrust load and restoring moments, drag torque, and 27 force and moment coefficients. The effects of misalignment on the dynamic performance of a refrigerant fluid-hybrid thrust bearing are evaluated at an optimal operating condition. The axial force/displacement stiffness coefficient and the direct moment/angle stiffness coefficients show a maximum for a certain recess pressure ratio, while the damping coefficient steadily increases with the applied load. As the misalignment angle increases, both moment and force coefficients also increase. Most operating conditions show a whirl frequency ratio equal to 0.50. Thus, thrust hybrid bearings offer the same limited stability characteristics as hydrodynamic thrust bearings when undergoing self-excited shaft angular motions.
Modeling of Heat Transfer in a Mist/Steam Impinging Jet
Authors: Li X. , Gaddis J. L. , Wang T.
Published: July 2002

The addition of mist to a flow of steam or gas offers enhanced cooling for many applications, including cooling of gas turbine blades. The enhancement mechanisms include effects of mixing of mist with the gas phase and effects of evaporation of the droplets. An impinging mist flow is attractive for study because the impact velocity is relatively high and predictable. Water droplets, less than 15 μm diameter and at concentrations below 10 percent, are considered. The heat transfer is assumed to be the superposition of three components: heat flow to the steam, heat flow to the dispersed mist, and heat flow to the impinging droplets. The latter is modeled as heat flow to a spherical cap for a time dependent on the droplet size, surface tension, impact velocity and surface temperature. The model is used to interpret experimental results for steam invested with water mist in a confined slot jet. The model results follow the experimental data closely.
Structural Health Monitoring Using Statistical Pattern Recognition Techniques
Authors: Sohn Hoon , Farrar Charles R. , Hunter Norman F. , Worden Keith
Published: July 2002

This paper casts structural health monitoring in the context of a statistical pattern recognition paradigm. Two pattern recognition techniques based on time series analysis are applied to fiber optic strain gauge data obtained from two different structural conditions of a surface-effect fast patrol boat. The first technique is based on a two-stage time series analysis combining Auto-Regressive (AR) and Auto-Regressive with eXogenous inputs (ARX) prediction models. The second technique employs an outlier analysis with the Mahalanobis distance measure. The main objective is to extract features and construct a statistical model that distinguishes the signals recorded under the different structural conditions of the boat. These two techniques were successfully applied to the patrol boat data clearly distinguishing data sets obtained from different structural conditions.
Limits of the Turbine Efficiency for Free Fluid Flow
Authors: Gorban’ Alexander N. , Gorlov Alexander M. , Silantyev Valentin M.
Published: July 2002

An accurate estimate of the theoretical power limit of turbines in free fluid flows is important because of growing interest in the development of wind power and zero-head water power resources. The latter includes the huge kinetic energy of ocean currents, tidal streams, and rivers without dams. Knowledge of turbine efficiency limits helps to optimize design of hydro and wind power farms. An explicitly solvable new mathematical model for estimating the maximum efficiency of turbines in a free (nonducted) fluid is presented. This result can be used for hydropower turbines where construction of dams is impossible (in oceans) or undesirable (in rivers), as well as for wind power farms. The model deals with a finite two-dimensional, partially penetrable plate in an incompressible fluid. It is nearly ideal for two-dimensional propellers and less suitable for three-dimensional cross-flow Darrieus and helical turbines. The most interesting finding of our analysis is that the maximum efficiency of the plane propeller is about 30 percent for free fluids. This is in a sharp contrast to the 60 percent given by the Betz limit, commonly used now for decades. It is shown that the Betz overestimate results from neglecting the curvature of the fluid streams. We also show that the three-dimensional helical turbine is more efficient than the two-dimensional propeller, at least in water applications. Moreover, well-documented tests have shown that the helical turbine has an efficiency of 35 percent, making it preferable for use in free water currents.
Measurements in a Turbine Cascade Flow Under Ultra Low Reynolds Number Conditions
Authors: Van Treuren Kenneth W. , Simon Terrence , von Koller Marc , Byerley Aaron R. , Baughn James W. , Rivir Richard
Published: July 2002

With the new generation of gas turbine engines, low Reynolds number flows have become increasingly important. Designers must properly account for transition from laminar to turbulent flow and separation of the flow from the suction surface, which is strongly dependent upon transition. Of interest to industry are Reynolds numbers based upon suction surface length and flow exit velocity below 150,000 and as low as 25,000. In this paper, the extreme low end of this Reynolds number range is documented by way of pressure distributions, loss coefficients, and identification of separation zones. Reynolds numbers of 25,000 and 50,000 and with 1 percent and 8-9 percent turbulence intensity of the approach flow (free-stream turbulence intensity, FSTI) were investigated. At 25,000 Reynolds number and low FSTI, the suction surface displayed a strong and steady separation region. Raising the turbulence intensity resulted in a very unsteady separation region of nearly the same size on the suction surface. Vortex generators were added to the suction surface, but they appeared to do very little at this Reynolds number. At the higher Reynolds number of 50,000, the low-FSTI case was strongly separated on the downstream portion of the suction surface. The separation zone was eliminated when the turbulence level was increased to 8-9 percent. Vortex generators were added to the suction surface of the low-FSTI case. In this instance, the vortices were able to provide the mixing needed to re-establish flow attachment. This paper shows that massive separation at very low Reynolds numbers (25,000) is persistent, in spite of elevated FSTI and added vortices. However, at a higher Reynolds number, there is opportunity for flow reattachment either with elevated free-stream turbulence or with added vortices. This may be the first documentation of flow behavior at such low Reynolds numbers. Although it is undesirable to operate under these conditions, it is important to know what to expect and how performance may be improved if such conditions are unavoidable.
A Fractional-Diffusion Theory for Calculating Thermal Properties of Thin Films From Surface Transient Thermoreflectance Measurements
Authors: Kulish Vladimir V. , Lage Jose´ L. , Komarov Pavel L. , Raad Peter E.
Published: July 2002

The transient thermoreflectance (TTR) method consists of measuring changes in the reflectivity of a material (thin film) under pulsed laser heating, and relating these changes to the corresponding surface temperature variations. Analytical solutions of the diffusion problem are then used to determine the thermal conductivity of the material following an iterative matching process between the solutions and the experimental results. Analytical solutions are attainable either when the material absorbs the laser energy volumetrically or when the material absorbs the laser energy at the surface. Either solution allows for the determination of only one thermal property (thermal conductivity or diffusivity), with the other one assumed to be known. A new, single, analytical solution to the transient diffusion equation with simultaneous surface and volumetric heating, found using fractional calculus, is presented in a semi-derivative form. This complete solution provides the means to determine the two thermal properties of the material (thermal conductivity and diffusivity) concomitantly. In this preliminary study, the solution component for surface heating is validated by comparison with experimental data for a gold sample using the classical thermoreflectance method. Further results, for surface and volumetric heating, are obtained and analyzed considering a GaAs sample.
Virtual Skyhook Vibration Isolation System
Authors: Griffin Steve , Gussy Joel , Lane Steven A. , Henderson Benjamin K. , Sciulli Dino
Published: July 2002

This work presents and demonstrates a passive isolation system that offers the performance of a skyhook damper, but without the need of an inertial reference. This “virtual skyhook” isolation system can be used to reduce the transmission of base excitations to a structure. An analysis of the concept is presented, and model predictions are compared to experimental measurements for a simple test structure. The results demonstrate that the proposed isolation system significantly attenuates transmissibility at resonance without the penalty of increased transmissibility at higher frequencies, which often limits the performance of passive approaches. Practical issues regarding the design and implementation of the virtual skyhook vibration isolation system are also presented and discussed. To the best of the authors’ knowledge, this is the first experimental demonstration of an entirely passive skyhook damper isolation system.
Numerical Simulation of Real-Gas Flow in a Supersonic Turbine Nozzle
Ring
Authors: Hoffren J. , Talonpoika T. , Larjola J. , Siikonen T.
Published: July 2002

In small Rankine cycle power plants, it is advantageous to use organic media as the working fluid. A low-cost single-stage turbine design together with the high molecular weight of the fluid leads to high Mach numbers in the turbine. Turbine efficiency can be improved significantly by using an iterative design procedure based on an accurate CFD simulation of the flow. For this purpose, an existing Navier-Stokes solver is tailored for real gas, because the expansion of an organic fluid cannot be described with ideal gas equations. The proposed simulation method is applied for the calculation of supersonic flow in a turbine stator. The main contribution of the paper is to demonstrate how a typical ideal-gas CFD code can be adapted for real gases in a very general, fast, and robust manner.
Theoretical and Experimental Analysis of Nonlinear Dynamics in a Linear Compressor
Authors: Choe Gyu-Sang , Kim Kwang-Joon
Published: July 2002

Steady-state nonlinear response characteristics of a linear compressor are investigated theoretically and experimentally. In the theoretical approach, motions of not only piston but also cylinder are considered and dynamic models for steady-state response predictions are formulated by applying the describing function method. Effects of piston mass on the jump phenomena are predicted by the derived models as an example of design parameter variation and compared with actual experimental results.
Generalized Kinematic Modeling of Reconfigurable Machine Tools
Authors: Moon Yong-Mo , Kota Sridhar
Published: July 2002

To accommodate frequent changes in product design and to be able to process a family of products in a timely and cost-effective manner, the next generation of machine tools should be reconfigurable. Reconfigurability enables reduction not only in machine design lead time but more significantly a reduction in machine set-up and ramp-up time. The essential characteristics of Reconfigurable Machine Tools (RMTs) include modularity, convertibility, flexibility, and cost-effectiveness. This paper presents a mathematical representation scheme using screw theory that lays the foundation for systematic design of reconfigurable machine tools. The motion characteristics of a set of desired machining tasks as well as stored library of machine modules are captured in a common representation scheme. A simple design example to illustrate the application of this methodology for systematic selection and synthesis of reconfigurable machine tools is presented.
An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels
Authors: Garimella S. , Killion J. D. , Coleman J. W.
Published: July 2002

This paper reports the development of an experimentally validated model for pressure drop during intermittent flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were then used to identify data that corresponded to the intermittent flow regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the flow of liquid between the film and slug to the pressure drop were included. Empirical data from the literature for the relative length and velocity of the slugs and bubbles, and relationships from the literature for the pressure loss associated with the mixing that occurs between the slug and film were used with assumptions about individual phase friction factors, to estimate the total pressure drop in each unit cell. A simple correlation for non-dimensional unit-cell length based on slug Reynolds number was then used to estimate the total pressure drop. The results from this model were on average within ±13.4% of the measured data, with 88% of the predicted results within ±25% of the 77 measured data points.
Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel
Authors: Okajima Atsushi , Kosugi Takashi , Nakamura Akira
Published: July 2002

Flow-induced in-line oscillation of a circular cylinder has been experimentally studied by free-oscillation tests in a water tunnel. Response amplitudes of a circular cylinder have been measured for determining the values of the reduced mass-damping parameter of less than 1.0. In the free-oscillation tests, the cylinder models were spring-mounted so as to oscillate as a two-dimensional rigid cylinder in the water tunnel. Two types of excitation phenomena appear at approximately half of the resonance flow velocity. The response amplitudes are sensitive to the reduced mass-damping parameter during the in-line oscillation of the first excitation region with a symmetric vortex street, and the alternate vortices are periodically shed, locking-in with the vibration of the cylinder in the second excitation region. A hysteresis phenomenon is observed to appear in the in-line oscillation of the latter region. A cantilevered circular cylinder with a finite length aspect ratio of 10 was tested for fluid-elastic characteristics of the cylinder, and these characteristics are found to be quite different from those of the two-dimensional cylinder, having only one wide velocity region of excitation. The results of this study are providing important supporting data for the recent publication “Guideline for Evaluation of Flow-Induced Vibration of a Cylindrical Structure in a Pipe,” by the Japan Society of Mechanical Engineers, Standard JSME S012-1998.
Multi-Mode Driving Control of a Parallel Hybrid Electric Vehicle Using Driving Pattern Recognition
Authors: Jeon Soon-il , Jo Sung-tae , Park Yeong-il , Lee Jang-moo
Published: July 2002

Vehicle performance such as fuel consumption and catalyst-out emissions is affected by a driving pattern, which is defined as a driving cycle with grades in this study. To optimize the vehicle performances on a temporary driving pattern, we developed a multi-mode driving control algorithm using driving pattern recognition and applied it to a parallel hybrid electric vehicle (parallel HEV). The multi-mode driving control is defined as the control strategy which switches a current driving control algorithm to the algorithm optimized in a recognized driving pattern. For this purpose, first, we selected six representative driving patterns, which are composed of three urban driving patterns, one expressway driving pattern, and two suburban driving patterns. A total of 24 parameters such as average cycle velocity, positive acceleration kinetic energy, stop time/total time, average acceleration, and average grade are chosen to characterize the driving patterns. Second, in each representative driving pattern, control parameters of a parallel HEV are optimized by Taguchi method though the fuel-consumption and emissions simulations. And these results are compared with those by parametric study. There are seven control parameters, six of them are weighting factors of performance measures for deciding the ratio of engine power to required power from driving load. And the other is the charging/discharging method of battery. Finally, in driving, a neural network (the Hamming network) decides periodically which representative driving pattern is closest to a current driving pattern by comparing the correlation related to 24 characteristic parameters. And then the current driving control algorithm is switched to the optimal one, assuming the driving pattern does not change in the next period.
Frequency Distributions for Hourly and Daily Clearness Indices
Authors: Iban˜ez Manuel , Beckman William A. , Klein Sanford A.
Published: July 2002

The clearness index for hourly and daily radiation is an important parameter in describing solar radiation. Liu and Jordan demonstrated that the monthly average daily clearness index could be used to predict the long-term distribution of daily solar radiation in a month. This paper reviews recent literature on the prediction of hourly and daily frequency distributions and cumulative frequency distributions of clearness indices. Ten years of measured weather data for six cities in the U.S. are used to investigate the nature of the hourly and daily frequency distributions. A second set of ten years of data for six cities is used to verify the predictions. A bi-exponential probability density function is proposed that fits the observed bimodal nature of the data better than existing models. A case is made for the function being universal.
Anisotropic Yield Locus Evolution During Cold Pilgering of Titanium
Alloy Tubing
Authors: Davies Richard W. , Khaleel Mohammad A. , Kinsel William C. , Zbib Hussein M.
Published: July 2002

The cold pilger metal forming technique is known to produce round titanium alloy tubing with mechanical properties that may be significantly anisotropic. These mechanical properties are of interest to both the manufacturers and consumers for defining initial manufacturing limitations and defining the final product design limitations. This study focuses on experimentally characterizing the yield locus development of Ti-3Al-2.5V seamless tubing during cold pilgering and a subsequent thermal stress relieving process. The materials are experimentally characterized using a biaxial testing apparatus, which subjects the specimen tubes to combined axial load and internal pressure. The Hill yield criterion is subsequently fit to the experimental results producing continuous yield loci. Each specimen is also experimentally characterized using X-ray diffraction to gain insight into the material textures that accompany the macroscopic properties. All work is focused on one particular pilger pass at two different production rates. A second experimental variable is introduced to the study by using two significantly different input materials, as characterized by X-ray diffraction. This study also investigates the nature of the plastic deformation of the tubing developed during cold pilgering via finite element analysis and discusses the relationship between the finite element predictions and the mechanical anisotropy.
Finite Element Analysis of Dynamically Loaded Journal Bearings: Influence of the Bolt Preload
Authors: Stefani Fabrizio A. , Rebora Alessandro U.
Published: July 2002

An improved FEM model was developed to simulate the elastic behavior of a connecting rod bearing, accounting for the displacements caused by the tightening torque applied to the bolts that join the cap and the rod. These initial displacements are added to the pressure induced displacements, to enhance the solution of the elastohydrodynamic bearing lubrication problem. The big end bearing of a marine diesel engine was modeled and analyzed under combustion process loads and inertia loads using the Newton-Raphson method together with the Murty’s algorithm. Some important differences between these results and other results published for the same bearing without the bolt preload are identified and discussed.
Spreading Characteristics of Molecularly Thin Lubricant on Surfaces With Groove-Shaped Textures: Monte Carlo Simulation and Measurement Using PFPE Film
Authors: Zhang Hedong , Mitsuya Yasunaga , Yamada Maiko
Published: July 2002

Spreading characteristics of molecularly thin lubricant on a grooved surface have been studied numerically by Monte Carlo simulations and compared with measurements obtained by perfluoropolyether (PFPE) thin film spreading on a solid surface with minute grooves. In the simulations, by incorporating the interactions between molecules and the side surfaces of a groove, the Monte Carlo method based on the Ising model was extended to the case of a surface with grooves and applied to simulate the spreading of non-polar lubricant inside a groove. Compared with the spreading on a smooth surface, lubricant spreads rapidly inside a groove, indicating an acceleration of the spreading along the groove. In the experiments, lubricant spreading on a surface with groove-shaped textures was measured by making use of the phenomenon in which diffracted light decreases or vanishes in the lubricant-covered region. Based on the results showing lubricant spreading predominantly along the groove, the accelerating effect obtained in the simulations is well confirmed by the measurements.
Effect of the Intermolecular Forces on the Flying Attitude of Sub-5 NM Flying Height Air Bearing Sliders in Hard Disk Drives
Authors: Wu Lin , Bogy D. B.
Published: July 2002

When the spacing between the slider and the disk is smaller than 10 nm, the effect of the intermolecular forces between the two solid surfaces can no longer be ignored. This effect on the flying attitude of practical slider designs is investigated here numerically. The three-dimensional slider surface is discretized into non-overlapping unstructured triangles. The intermolecular forces between each triangular cell of the slider and the disk surface are formulated, and their contributions to the total vertical force, as well as the pitch and roll moments, are included in a previously developed steady state air bearing design code based on a multi-grid finite volume method with unstructured triangular grids [3–5]. It is found that the van der Waals force has significant influence on the flying height and has non-negligible effect on the pitch angle for both positive pressure sliders and negative pressure sliders, when the flying height is below 5 nm. When the flying height is below 0.5 nm, the repulsive portion of the intermolecular force becomes important and also has to be included.
Models for Cyclic Ratchetting Plasticity—Integration and Calibration
Authors: Ekh Magnus , Johansson Anders , Thorberntsson Hans , Josefson B. Lennart
Published: July 2002

Three well-known ratchetting models for metals with different hardening rules were calibrated using uniaxial experimental data from Bower (1989) [J. Mech. Phys. Solids, 31, pp. 455–470], and implemented in the FE code ABAQUS (Hibbitt et al., 1997 [ABAQUS Version 5.7]) to predict ratchetting results for a tension-torsion specimen. The models were integrated numerically by the implicit Backward Euler rule, and the material parameters were calibrated via optimization for the uniaxial experimental data. The algorithmic tangent stiffnesses of the models were derived to obtain efficient FE implementations. The calculated results for an FE model of the tension-torsion specimen were compared to experimental results. The model proposed by Jiang and Sehitoglu (1995) [Wear, 191, pp. 35–44] showed the best agreement both for the uniaxial and the structural component case. [S0094-4289(00)00701-5]
Creep Deformation and Failure: Effects of Randomness and Scatter
Authors: Harlow D. G. , Delph T. J.
Published: July 2002

A notable feature of replicated creep and creep-rupture data is the considerable amount of statistical scatter present. The existence of this scatter leads to substantial uncertainties in the predictions of creep deformation and failure. In this paper, we review the experimental evidence in this regard. We then survey recent efforts to construct models of creep deformation and rupture that include one or more aspects of this randomness. [S0094-4289(00)01703-5]
Integration of Basic Materials Research Into the Design of Cast Components by a Multi-Scale Methodology
Authors: Gall Ken , Horstemeyer Mark F.
Published: July 2002

We present a formal methodology to integrate basic materials research results into a design procedure for engineering components. Although the methodology is generic, we demonstrate its development and application in designing a cast automotive control arm. Specifically, we propose a multi-scale analysis whereby the local mechanisms of deformation are accounted for by an internal state variable constitutive model embedded within a non-linear elastic-plastic finite element analysis. Multiple fundamental materials research approaches at different length scales are utilized to quantify the pertinent deformation mechanisms, such as atomistic simulations, microscopy, micromechanical finite element simulations, and mechanical testing. The current methodology is a step toward a larger goal of interactively integrating basic materials science research into engineering system design. [S0094-4289(00)01903-4]
A Novel High Performance Die Attach for Ceramic Packages
Authors: Shi J. Z. , Xie X. M. , Stubhan F. , Freytag J.
Published: July 2002

A novel two-step process based on isothermal solidification is developed for die attachment of ceramic package. With a simple design of the multilayer system, silicon chip could be bonded onto the allumina substrate in between 200°C and 300°C. The total process time is less than 15 seconds during which the actual assembly time is within one second. Most of the samples can pass the shear strength test specified by MIL STD 883D. All the samples could pass 1750 cycles between −55°C and 125°C with slight degradation in die shear strength after the test. The microstructures of the bonds are characterized with metallographical investigation. Comparisons are made between the present technique and the Au/Si eutectic bonding. [S1043-7398(00)01202-0]
The Nonoriented, Multiple Passageway Flowline Connection System
Authors: Galle Gary , Bond Rudolf
Published: July 2002

The remote, diverless, simultaneous connection of multiple subsea flowlines has historically been a difficult and costly operation. Difficulties and intensified operational activities stem from the need to orient the multiple flow paths prior to the final connection of the tubulars. This rotational orientation has proven to be very difficult for randomly prelaid flowlines or flowlines which must be rotated a relatively large amount prior to makeup. A new, innovative method has been developed whereby multiple flowlines can be connected without¯ the need to rotationally orient the multiple tubulars. This new connection system technology has undergone full-scale subsea testing and will be implemented in a major development in the North Sea. The significance of this achievement is assessed in this paper with a focus on the design philosophies used, the principles of operation, the overall system reliability, the projected amount of operational cost reduction, and the full-scale testing results. Additional comments are made concerning the applicability of this technology in various other subsea applications. [S0195-0738(00)00501-X]
Aerodynamic Torque of a Butterfly Valve—Influence of an Elbow on the Time-Mean and Instantaneous Aerodynamic Torque
Authors: Danbon F. , Solliec C.
Published: July 2002

Many technological devices use butterfly valves to control the flow of the process or as safety unit. The principal advantages of this type of valve are their simplicity, their low cost, their speed of closing and the weak pressure drop which they produce when they are completely open. For installations of large size, the actuator of the valve can be very expensive; thus it is essential to know well the fluid forces and the resulting torque exerted on the valve. Consequently, the variation of the shaft torque of the butterfly valves according to the opening is of great interest to calculate the power of the actuator. Initially the flow around the valve is characterized by means of hot wire anemometry. It is noted that the disturbances induced by the elbow and/or the valve are felt until a distance from approximately 8 times the pipe diameter. A method of direct measurement by torquemeter and an indirect method by integration of the pressure forces on the faces of the valve give access to the time-mean and instantaneous torque on the valve shaft. Comparisons between the direct and indirect measurement of the torque are made before engaging the analysis of the results. Close to the full opening, the torque presents fluctuations harmful to suitable lifespan of the valve. Compared to the straight pipe case, the temporal and spectral analyses of the instantaneous torque prove that the elbow induces important fluctuations when the valve is completely open. Several tests carried out according to the valve/elbow spacing show that these effects disappear beyond a distance from 8 to 10 times the diameter of the pipe. [S0098-2202(00)02902-3]
On the Integration of Layered Manufacturing and Material Removal Processes
Authors: Kulkarni Prashant , Dutta Debasish
Published: July 2002

In this paper, we develop methodologies for the integration of layered manufacturing and traditional material removal processes into an integrated manufacturing setup. The scenarios under which this integration would be beneficial are identified and algorithms for the integration developed. As examples, we consider two current layered manufacturing technologies that use material removal operations as a part of their process. The benefits of our procedure are demonstrated by examples. [S1087-1357(00)00701-2]
Bulk-Flow Analysis of Hybrid Thrust Bearings for Process Fluid Applications
Authors: San Andre´s Luis
Published: July 2002

Advanced cryogenic fluid turbopumps are very compact, operate at extremely high shaft speeds, and require hybrid (hydrostatic/hydrodynamic) radial and thrust fluid film bearings for accurate rotor positioning. Sound design and reliable operation of fluid film thrust bearings also allows for unshrouded impellers with a significant increase in the turbopump mechanical efficiency. A bulk-flow analysis for prediction of the static load performance and dynamic force coefficients of high speed, angled injection orifice-compensated, hybrid (hydrostatic/hydrodynamic) thrust bearings is presented. The model accounts for the bulk-flow mass, momentum and thermal energy transport, and includes flow turbulence and fluid inertia (advection and centrifugal) effects on the bearing film lands and recesses. The performance of a refrigerant hybrid thrust bearing for an oil-free air conditioning equipment is evaluated at two operating speeds and pressure differentials. The computed results are presented in dimensionless form to evidence consistent trends in the bearing performance characteristics. As the applied axial load increases, the bearing film thickness and flow rate decrease while the recess pressure increases. The axial stiffness coefficient shows a maximum for a certain intermediate load while the damping coefficient steadily increases with load. The computed results show the significance of centrifugal fluid inertia at low recess pressures (i.e. low loads) and high rotational speeds, and which can lead to film starvation at the bearing inner radius and subambient pressures just downstream of the bearing recess edge. [S0742-4787(00)02201-3]
Operation of Foil Bearings Beyond the Bending Critical Mode
Authors: Heshmat Hooshang
Published: July 2002

A series of experiments were conducted to determine a foil bearings ability to operate in the region of the bending mode of a flexible rotor. Three different bearings, spaced at three different positions along the shaft, were tested in order to make super-bending-critical operation possible. This was achieved with a proper bearing design located at an optimum position with respect to the bending nodes. After proper trim balancing the bearings passed the 34,100 rpm first bending critical and went on to operate up to 85,000 rpm, 2.5 times the bending critical. Throughout, the amplitudes of vibration remained small. The documented ability of these bearings to operate in the domain of a flexible rotor’s bending mode makes these bearings a prime candidate for the high-speed machinery of modern technology. [S0742-4787(00)02401-2]
Analysis of Stresses Induced by Dynamic Load Head-Disk Contacts
Authors: Fu Ta-Chang , Bogy David B.
Published: July 2002

The dynamic load head-disk contact induced impact stress was studied. A dual channel LDV was used to measure the head-disk relative motion during impact, and an analytical model incorporating the Hertz theory of impact was developed to quantitatively estimate the impact induced contact force and stress based on the LDV-measured results. 70 percent sliders were used in order to compare the results with our previous study. From the estimated maximum contact stresses and the results of our previous study, it was found that when the average maximum stress was 511 MPa, the head-disk interface did not show any damage after 100,000 cycles of repeated head-disk impacts. When the average maximum stress was 880 MPa, however, 100,000 repeated head-disk impacts caused significant wear of the disk’s overcoat even though a single impact did not cause any observable damage. From the analysis it can be seen that a lower head-disk impact velocity and/or a larger radius of curvature at the contacting corner of the slider result in a smaller head-disk impact stress on the disk. Based on the analyses, we estimated the radius of curvature needed for a 50 percent (Nano) slider and a 30 percent (Pico) slider to have at least 100,000 cycles of dynamic load head-disk interface durability. Such radius of curvature can be realized, for example, by edge-blending the sliders. [S0742-4787(00)02901-5]
Thermoelastic Asperity Contacts, Frictional Shear, and Parameter Correlations
Authors: Liu Geng , Wang Qian
Published: July 2002

A thermoelastic asperity contact model has been developed for two-dimensional problems. This model takes into account a steady-state heat transfer and the asperity distortion due to thermoelastic deformations. The work reported in this paper further refines the thermoelastic model to include the shear traction effect on the thermoelastic stress distributions and derives semi-empirical relations for the contact pressure, temperature, asperity separation, and contact area, as functions of friction, asperity properties, and material properties. A method of boundary constraint coefficients is developed to facilitate the stress analyses of a half space using a finite computation domain. [S0742-4787(00)04001-7]
A Mixed Soft Elastohydrodynamic Lubrication Model With Interasperity Cavitation and Surface Shear Deformation
Authors: Shi Fanghui , Salant Richard F.
Published: July 2002

A deterministic mixed lubrication model, governing the interface between a moving smooth rigid surface and a stationary rough elastic surface, has been developed. Both the normal and shear deformations of the elastic surface are considered, as well as interasperity cavitation. Utilizing an analogy between the hydrodynamic lubrication (with cavitation) problem and the asperity contact problem, a generalized computational formulation is derived and a unique solution scheme constructed to solve these seemingly different problems. The model has been applied to the rotary lip seal, and used to predict the performance characteristics over a range of shaft speeds. [S0742-4787(00)04101-1]
THD Analysis of Tilting Pad Thrust Bearings—Comparison Between Theory and Experiments
Authors: Almqvist T. , Glavatskikh S. B. , Larsson R.
Published: July 2002

The objective of the present research is to verify a THD model of hydrodynamic thrust bearings. The developed model of a pivoted pad bearing, which can tilt both radially and circumferentially, allows for three-dimensional temperature distribution in the oil film and in the pad, as well as two-dimensional temperature variation in the runner. Viscosity and density are treated as functions of both temperature and pressure. Experiments have been performed on a test rig, containing two identical equalizing pivoted pad thrust bearings. Power loss, runner temperature, and pressure profiles as a function of load and rotational speed are compared for both theoretical and experimental investigations. Fairly good agreement has been found when the oil inlet temperature and heat transfer coefficients have been estimated in order to get the same runner temperature in both theory and experiment. [S0742-4787(00)00802-X]
Effects of Orientation Angles on Film Cooling Over a Flat Plate: Boundary Layer Temperature Distributions and Adiabatic Film Cooling Effectiveness
Authors: Jung In Sung , Lee Joon Sik
Published: July 2002

Presented are experimental results describing the effects of orientation angle of film cooling holes on boundary layer temperature distributions and film cooling effectiveness. Film flow data were obtained from a row of five film cooling holes on a flat test plate. The inclination angle of the hole was fixed at 35 deg and four orientation angles of 0, 30, 60, and 90 deg were investigated. The velocity ratios surveyed were 0.5, 1.0, and 2.0. The boundary layer temperature distributions were measured at three downstream locations using 1μm platinum wire. Detailed adiabatic film cooling effectiveness distributions were measured using thermochromic liquid crystal. Results show that the increased lateral momentum in the case of large orientation angle injection strongly affects boundary layer temperature distributions. Temperature distribution characteristics are, in general, explained in the context of the interactions between injectant and free-stream fluid and between injectants issuing from adjacent holes. The adiabatic film cooling effectiveness distributions are discussed in connection with the boundary layer temperature distributions. Spanwise-averaged effectiveness distributions and space-averaged effectiveness distributions are also presented with respect to the velocity ratios and the orientation angles. [S0889-504X(00)01701-3]