bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freezing of a Salt Solution in a Packed Bed
Authors: Chellaiah S. , Singh H. 
Published: February 2008

Abstract
There are many natural processes and technological applications that involve the solidification of a binary solution saturating a porous matrix. Some of them are: natural freezing and artificial freezing (for construction purposes) of soil, oil exploration in cold regions, and processing and preservation of food. This paper presents the results of a fundamental study of freezing of a binary salt solution saturating a packed bed. An aqueous sodium chloride solution (of noneutectic composition) constituted the binary solution and spherical glass beads constituted the packed bed. The freezing was initiated at one of the vertical walls of a rectangular cavity. The temperature distributions in the solid, mush, and liquid regions were recorded using thermocouples. The concentration of salt was determined using a sample withdrawal technique in conjunction with a refractometer and a calibration chart. There was buoyancy-driven convective flow generated and sustained by the thermal and solutal gradients. The effect of this flow on the freezing process was significant. The morphology of the freezing fronts, the temperature and salt concentration profiles, and the rate of freezing were all influenced by the flow. Even in experiments with an initial superheat of 10°C, it was found that the effect of flow was considerable. For even though the fluid flows through the interstitial spaces in the porous matrix, the permeability was large for balls of 0.5-in. diameter. With a superheat of 20°C, the convection was vigorous and the rate of freezing was retarded considerably. The salt rejected during freezing was redistributed by the flow. At later times, a stable solute-rich region formed at the bottom of test cell where the concentration decreased with height. The amount of salt rejected was directly influenced by the rate of freezing, which in turn was controlled by the superheat and the permeability of packed bed.
Performance of the Biplane Wells Turbine
Authors: Gato L. M. C. , Curran R. 
Published: February 2008

Abstract
The paper describes the experimental investigation of the biplane Wells turbine for use on a wave power plant. The performance of the biplane turbine was tested in unidirectional steady air flow by varying the model configurations using solidity, gap-to-chord ratio, and rotor stagger angle. It was found that the gap-to-chord ratio and stagger considerably influenced the performance of the biplane turbine due to the mutual interference between the rotor planes.
Strain Concentrations in Pipelines With Concrete
Coating
Authors: Ness O. B. , Verley R. 
Published: February 2008

Abstract
This paper concerns the strain distribution, and in particular strain concentration in field joints, for concrete-covered pipelines during laying. A semi-analytical model, full-scale tests to verify the model, and results of a parameter study are described. The model is used to establish nonlinear moment-curvature curves at a number of cross sections on the concrete-coated pipe and in the field joint (FJ). These are used to establish a strain concentration factor (SCF) for the FJ, or characteristics for a varying stiffness model of a pipe for direct use in lay analyses. Constant moment, four-point bending tests have been conducted on 16-in and 20-in dia, concrete-coated pipes as well as material tests on the pipe steel, corrosion coating and concrete. The behavior of the pipe, and in particular the SCF at the field joints, is investigated and compared to predictions using the semi-analytical model. The model is found to give a good prediction of the SCF and strain distribution along the pipe joint, for both the steel and the concrete, and is suitable for use in lay analyses for the overbend of S-mode lay vessels.
Sum-Frequency Diffraction Loads on Tension-Leg Platforms in
Bidirectional Waves
Authors: Vazquez J. H. , Williams A. N. 
Published: February 2008

Abstract
Second-order diffraction theory is utilized to compute the sum-frequency diffraction loads on a deepwater tension-leg platform (TLP) in bidirectional waves. The linear diffraction solution is obtained utilizing a Green function approach using higher-order boundary elements. The second-order hydrodynamic loads explicitly due to the second-order potential are computed using the indirect, assisting radiation potential method. An efficient numerical technique is presented to treat the free-surface integral which appears in the second-order load formulation. Numerical results are presented for a stationary ISSC TLP in water of infinite depth. It is found that wave directionality may have a significant influence on the second-order hydrodynamic loads on a TLP and that the assumption of unidirectional waves does not always lead to conservative estimates of the sum-frequency loading.
A Two-Way Nesting Procedure for the WAM Model: Application to the
Spanish Coast
Authors: Gomez Lahoz M. , Carretero Albiach J. C. 
Published: February 2008

Abstract
The performance of the standard one-way nesting procedure for a regional application of a third-generation wave model is investigated. It is found that this nesting procedure is not applicable when the resolution has to be enhanced drastically, unless intermediate grids are placed between the coarse and the fine grid areas. This solution, in turn, requires an excess of computing resources. A two-way nesting procedure is developed and implemented in the model. Advantages and disadvantages of both systems are discussed. The model output for a test case is compared with observed data and the results are discussed in the paper.
Field Verification of Linear and Nonlinear Hybrid Wave Models for
Offshore Tower Response Prediction
Authors: Couch A. T. , Conte J. P. 
Published: February 2008

Abstract
Accuracy of the prediction of the dynamic response of deepwater fixed offshore platforms to irregular sea waves depends very much on the theory used to determine wave kinematics. A common industry practice consists of using linear wave theory, which assumes infinitesimal wave steepness, in conjunction with empirical wave stretching techniques to provide a more realistic representation of near-surface water kinematics. The current velocity field is then added to the wave-induced fluid velocity field and the wave-and-current forces acting on the structure are computed via Morison’s equation. The first objective of this study is to compare the predicted responses of Cognac, a deepwater fixed platform, obtained from several popular empirical wave models with the response Cognac predicted based on the hybrid wave model. The latter is a recently developed higher-order, and therefore more accurate, wave model which satisfies, up to the second-order in wave steepness, the local mass conservation and the linear free surface boundary conditions at the instantaneous wave surface. The second objective of this study is to correlate the various analytical response predictions with the measured response of Cognac. Availability of a set of oceanographic and structural vibration data for Cognac provides a unique opportunity to evaluate the prediction ability of traditional analytical models used in designing such structures. The results of this study indicate that (i) the use of the hybrid wave model provides predicted platform response time histories which overall are in better agreement with the measured response than the predictions based on the various stretched linear wave models; and (ii) the Wheeler stretching technique produces platform response time histories which overall are more accurate than those obtained by using the other stretching schemes considered here.
Analysis of a Gas Lubricated Hydrodynamic Thrust
Bearing
Authors: Hughes S. J. , Hogg S. I. , Jones T. V. 
Published: February 2008

Abstract
Experimental results from a gas thrust bearing test facility are reported in this paper. This fundamental investigation of the thermo-fluid dynamics of a gas lubricated bearing forms part of a wider programme aimed at their introduction into the aeroengine environment. The experiments provide the most detailed measurements to date of a hydrodynamic lubrication film which uses gas as a working fluid. The bearing tested was lubricated with air. The thrust pads had an outer radius of 0.125 m and during operation the clearance between the bearing surfaces was typically 10 μm. The design speed of the bearing was 10,000 rpm. Mean pad pressure and temperature distributions are presented for a range of bearing loads up to 3/4 kN, which were measured under steady operating conditions. Transient pressure and surface clearance measurements from fast response probes are also reported. These measurements show a complex relative motion of the bearing surfaces, the exact nature of which could only be determined from a more detailed set of surface clearance measurements than those in the present work. However, the transient pressure measurements show that these surface clearance fluctuations do not exert a strong influence on the lubrication film pressures, which can be considered to be essentially steady. The test data are compared with predictions obtained by solving Reynolds equation numerically, using a finite-volume based procedure. Thermal distortion of the bearing surface is not included in the model and this limits the agreement between measurements and calculations. The results suggest that this must be accounted for in the design of practical bearing systems, even though the lubrication film can be treated as isothermal. The measurements also show evidence of the inlet effects which raise the static pressure of the flow entering the bearing to above the ambient level.
Performance of a Powder Lubricated Journal Bearing With
WS2 Powder: Experimental Study
Authors: Heshmat H. , Brewe D. E. 
Published: February 2008

Abstract
Previous investigations have demonstrated the principle and feasibility of quasi-hydrodynamic lubrication using powders. With conventional lubricants, the hydrodynamic behavior of a journal bearing can be summarized in the form of a plot of friction coefficient against a nondimensional load parameter, usually referred to as a Stribeck curve. One of the main features of the curve is that, as the thickness of the lubricant film increases, the friction coefficient initially decreases until it reaches a minimum and then increases due to shearing of the lubricant film. Previous tests on a three pad journal bearing using molybdenum disulfide powder as the lubricant showed that its friction/load characteristics followed the Stribeck form. The experimental work reported herein describes further tests carried out on a three-pad journal bearing to evaluate its thermal stability and long term wear characteristics using tungsten disulfide powder as the lubricant. Dry tungsten disulfide powder lubricant has been shown to provide excellent wear resistance. Its friction properties are similar to molybdenum disulfide but it can be used at much higher temperatures. Bearing tests were carried out at speeds up to 30,000 rpm and loads up to 236 N. Over the load/speed range stable thermal operation was achieved. From friction torque measurements it was found that the coefficient of friction for the bearing was essentially constant over the range of loads and speeds. Unlike liquids, powders have a limiting shear strength property. When the limiting shear stress is reached in a powder flow, the powder essentially shears along a plane and does not flow in a viscous manner. The constant friction coefficient seen with the tungsten disulfide powder suggests that the powder had a low limiting shear strength and that this dominated the operation of the bearing in the tests. The total accumulated test time was more than eighteen hours. Periodically, the test journal and bearing pads were inspected but there was no measurable wear or visible damage.
Head-Disk Interface Performance With a Starved Liquid
Bearing—Analytical Solution to Reynolds Equation in the Near-Contact
Regime
Authors: Streator J. L. 
Published: February 2008

Abstract
Further increase in magnetic recording density requires a reduction in slider flying height. The current study employs the short-bearing approximation to determine analytically the static equilibrium configuration of a slider supported by a starved liquid bearing that operates between ideally smooth surfaces. The solution incorporates rheological behavior based on previously acquired data. The accuracy of the short-bearing approximation is assessed by determining how well the resulting solution satisfies the Reynolds equation. The analysis suggests a means of designing a slider to achieve head/medium spacings in the neighborhood of 20 nm.
Experimental Study of Freely Alignable Journal Bearings—Part 2:
Dynamic Characteristics
Authors: Qiu Z. L , Tieu A. K. 
Published: February 2008

Abstract
The traditional harmonic excitation method was modified to estimate 16 dynamic force coefficients of two misaligned journal bearings. To avoid the effects of different running conditions on the estimated coefficients, two harmonic forces with different frequencies were excited on the rotor simultaneously and all data were acquired during one test run. The excitation forces and their displacement responses were transferred to the frequency domain in which eight linear (complex) equations are derived. All 16 bearing force coefficients can then be obtained by solving these simultaneous linear equations through one operation. Applicable experimental procedures and data processing techniques are presented. The force coefficients of two circular journal bearings with two axial grooves each are estimated and correlate well with theoretical values when misalignment is considered. Various experimental errors are discussed and the uncertainty in the estimated coefficients is analyzed.
Three-Dimensional Measurement of Head Flying Height and Attitude
Using Image Processing of Fringe Patterns Formed by Michelson Laser
Interferometry
Authors: Mitsuya Yasunaga , Mitsui Akihito , Kawabe Yasuyuki , Lunde Lars 
Published: February 2008

Abstract
In-situ measurement of head flying height and attitude using image processing of fringe patterns formed by Michelson interferometry is studied. A wide laser beam is applied to illuminate the slider back surface and disk surface simultaneously to create interferometric fringe patterns. Employing the relationships arising between the two fringe patterns, the calculation procedure is formulated to yield the slider’s parallel, pitch and roll displacements. Experimental fringe patterns are captured in a single visual field by a high-speed CCD camera. Image processing for a higher signal-to-noise ratio, such as smoothing, filtering, amplification and ridge line extraction is then applied to the image data. Additionally, average processing with respect to multiple fringe lines to produce higher accuracy is successfully applied. Measured values of flying height and pitch and roll displacements are confirmed to be in good accordance with the calculation results, demonstrating excellent applicability of the present method down to the near-contact region.
Elastohydrodynamic Lubrication of Air-Lubricated
Rollers
Authors: Chang Y. B. , Chambers F. W. , Shelton J. J. 
Published: February 2008

Abstract
The lubricating air film between two rotating rollers in close contact was studied numerically. The numerical model used in this study accounts for the effects of air compressibility, material deformation, and the slip flow which occurs when the air film thickness is not much larger than the mean-free-path of the air molecules. The air film profiles and the pressure profiles for the nip region between the rollers were calculated. It was found that the calculated air film thicknesses are lower than predicted by the liquid elastohydrodynamic calculation. From this study, equations for the minimum air film thickness, the air film thickness at the center of contact, and the amount of air that passes through the nip were obtained. This study has application to the prediction of the amount of air entrained in a winding roll.
Measurements of Friction in Cold Metal Rolling
Authors: Tabary P. E. , Sutcliffe M. P. F. , Porral F. , Deneuville P. 
Published: February 2008

Abstract
Measurements of friction in rolling of aluminium strip on an experimental mill are described. Friction depended most strongly on the ratio Λ of the smooth film thickness to the combined roughness of the roll and strip, and on the reduction in strip thickness. Whether the greater roughness was on the roll or on the strip was found to be unimportant. Varying the oil temperature from 40 to 60°C was also found to be of secondary importance. Profilometry results suggested that friction was determined by the mean film thickness between the surfaces. At the slowest speeds and smallest films, friction was close to the value of 0.09 found in separate measurements in a disk machine of the boundary additive properties. At the highest speed the friction values, which were less than 0.01, could be explained by hydrodynamic lubrication. The transition between these two extremes occurred when the film thickness was of the order of the additive molecule length of 3 nm.
Glide Avalanche Prediction From Surface Topography
Authors: Marchon B. , Kuo D. , Lee S. , Gui J. , Rauch G. C. 
Published: February 2008

Abstract
As the head/disk spacing continues to decrease, the demand for thin film disks with glide capability below 20 nm becomes more pressing. As a consequence, the design of such media requires an ever increasing control of the surface topography to a nanometer level. This paper is an attempt to analytically predict the intrinsic glide capability of a textured disk, given the knowledge of its peak height distribution, as measured by a surface profilometer. This model also takes into account the long wavelength component of the topography, or waviness, by treating it as an independent variable leading to a broadening of the peak height distribution. This analysis also predicts relationships between various roughness parameters. Experimental data obtained on a total of 27 media surfaces of various types compare favorably to the theoretical predictions.
Evaluation of Dynamic Coefficients of a Two-Lobe Journal Bearing
Using an Electrical Analogy Approach
Authors: Prashad Har 
Published: February 2008

Abstract
A theoretical approach to evaluating capacitance, resistance, capacitive reactance, and impedance of the lower and upper lobes of a two-lobe elliptical hydrodynamic journal bearing under various operating conditions is developed. It is established that the change in capacitance and resistance with the change in eccentricity ratios is nonlinear. The capacitance and resistance, thus determined, are correlated with the dynamic coefficients of bearings using an electrical analogy. It is found that the stiffness and damping coefficients are higher for two-lobe bearings as compared to those of cylindrical bearings having identical dimensional parameters and operating under similar conditions. The analysis may have the potential to diagnose the stability regime of a bearing through the bearing’s electrical parameters. The electrical analogy may be a useful alternative to conventional techniques.
Ultrathin Perfluoropolyether Films—Influence of Anchoring and
Mobility of Polymers on the Tribological Properties
Authors: Ru¨he J. , Novotny V. , Clarke T. , Street G. B. 
Published: February 2008

Abstract
The tribological behavior of ultrathin films of hydroxyl terminated perfluoropolyethers attached to smooth silicon surfaces was studied in pin-on-disk experiments. The frictional properties of the films, which consisted of either physically adsorbed or chemically bonded polymer or a combination of both, was measured in sliding contact and lubricant loss was studied simultaneously by scanning microellipsometry. Prior to these experiments the kinetics of attachment of the polymer to silicon surfaces and the behavior of the polymer at high temperatures was investigated in order to obtain reproducible conditions for the deposition of the lubricant films and to rule out the occurrence of thermal degradation during film deposition. The tribological investigations showed that the lifetime of the surfaces with the attached boundary lubricant was strongly dependent on the mode of attachment of the polymer. The best tribological behavior was observed in films which contained both chemisorbed and physically adsorbed material.
Rheological and Physical Studies of Lubricating Greases Before and
After Use in Bearings
Authors: Mas Rémy , Magnin Albert 
Published: February 2008

Abstract
Lithium soap and calcium complex soap-based lubricating greases are studied when fresh and after use in roller and ball bearings. Examination of the rheological properties of these greases using rotating rheometers reveals changes that have occurred during use in the bearings. These modifications are not uniform throughout the hearing. Physical and chemical analyses enable these modifications in rheological properties to be linked to variations in composition or structure, depending on the type of grease and bearing. Several mechanisms involved in lubricating a bearing with a lubricating grease are confirmed or clarified.
Phase Change in a Misaligned Mechanical Face Seal
Authors: Etsion I. , Pascovici M. D. 
Published: February 2008

Abstract
The combination of phase change, coning, and face misalignment in mechanical seals is studied. The seal performance is calculated using an implicit analytical solution of the thermohydrodynamic problem. It is found that phase change can be detrimental to the seal’s angular stiffness. It is also found that the boiling interface is practically axisymmetric, even at moderate face misalignment. Thus, future analyses of phase change with misalignment can be considerably simplified.
Reductions in Wear Rate of Carbon Samples Sliding Against Wavy Copper
Surfaces
Authors: Lin Jau-Wen , Bryant M. D. 
Published: February 2008

Abstract
Wear rates (μgm/s) versus rotor speed for carbon samples sliding against smooth and wavy copper rotors (250 μm thick copper sheets were attached to smooth and wavy steel and polycarbonate backings) were identical at some speeds, but at other speeds wear rates for the wavy rotors were almost half those of the smooth rotors. Slider vibrations (periodic, with period set by rotation) perpendicular to the sliding surface were measured and Fourier analyzed. Comparison of vibration spectral amplitudes to spectral amplitudes derived from surface profiles identified vibration modes dynamically enhanced by surface waviness on the wavy rotor. At speeds where wear rates on the wavy rotor were most reduced, amplitudes of certain modes in the vibration spectrum were most enhanced. For all these cases, the product of mode number times speed was nearly constant, suggesting resonance. Contact forces and contact voltage drop (due to a mA current flowing from slider to rotor) were measured and plotted versus time during all experiments. Friction coefficients rapidly varied between 0.1 and 0.4, but averaged 0.2. Traces of friction coefficient versus time for both wavy and smooth rotors were similar, even when wear rates plunged on the wavy rotor. There were no large jumps in the contact voltage drop data, suggesting that the slider never disconnected from any of the rotors. Photoelastic visualizations (Bryant and Lin, 1993) of slider-rotor interfaces revealed concentrated contact on the smooth rotors, but none on the wavy rotors. The absence (induced by vibration) of concentrated contact may have caused differences in wear rates. Appreciable reductions (up to 50 percent) in wear rate are possible by adding small surface waves to a rotor that induce micro-vibrations of the slider-spring-rotor contact system. The effect appears most pronounced at resonance.