bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of Frictional Vibration in Wet Clutches Considering
Poroelastic Properties of Paper-Based Facing
Authors: Hattori Y. , Kato T. 
Published: February 2008

Abstract
This paper presents a new theory on frictional vibrations of paper-based friction material considering the interaction between its deformation and the consequent lubricant flow inside it. A frictional vibration model is proposed, in which a poroelastic body saturated by a viscous liquid is introduced, and then a stability criterion is derived on the assumption that vibrations in two directions, tangential and normal, are coupled. Compared with the experiment, it is confirmed that the proposed criterion can predict the stability limit more accurately than the conventional one, which does not take the deformation of the friction material into account and depends only on the slope of friction coefficient versus sliding velocity. Based on the present criterion, influences of material properties on the stability to frictional vibrations are discussed.
Head/Disk Interface Contact Detection Using a Refined Acoustic
Emission Technique
Authors: O'Brien K. , Harris D. 
Published: February 2008

Abstract
A refined technique using Acoustic Emission has been developed for use in head/disk interface contact detection. These refinements are focused on the design parameters of the Acoustic Emission electronics, amplification and filter settings, which permit accurate and repeatable contact detection measurements. A technique for determining the slider body natural frequencies is described in order that the proper filter design parameters can be determined. Experiments confirm the existence of these frequencies for a Al2O3TiC 50 percent slider are in excess of 600 KHz.
Characteristics of Air Bearing Suction Force in Magnetic Recording
Disks
Authors: Peng Jih-Ping , Hardie Cal E. 
Published: February 2008

Abstract
Some fundamental characteristics of the subambient pressure air bearing suction force were investigated analytically and numerically. The performance of air bearing suction force is strongly determined by the cavity bearing number, in which the cavity region recess depth is used as the characteristic film thickness. Although the optimal recess depth for maximum, suction force varies for different operation conditions, the optimal cavity bearing number can be found in a wide range of applications. The analytical model was confirmed by a finite element analysis. Examples of different disc velocities, slider dimensions, and ambient pressure effect were presented.
An Efficient Numerical Procedure for Thermohydrodynamic Analysis of
Cavitating Bearings
Authors: Vijayaraghavan D. 
Published: February 2008

Abstract
In this paper, an efficient and accurate numerical procedure to determine the thermo-hydrodynamic performance of cavitating bearings is described. This procedure is based on the earlier development of Elrod for lubricating films, in which the properties across the film thickness are determined at Lobatto points and their distributions are expressed by collocated polynomials. The cavitated regions and their boundaries are rigorously treated. Thermal boundary conditions at the surfaces, including heat dissipation through the metal to the ambient, are incorporated. Numerical examples are presented comparing the predictions using this procedure with earlier theoretical predictions and experimental data. With a few points across the film thickness and across the journal and the bearing in the radial direction, the temperature profile is very well predicted.
Hydrodynamic Lubrication of Face Seal in a Turbulent Flow
Regime
Authors: Lin Jen Fin , Yao Chih Chung 
Published: February 2008

Abstract
Models for thermohydrodynamic lubrication in the turbulent regime are developed for a mechanical end face seal with various combinations of asperity height and roughness pattern. A surface wear model, based on deformation, is established for mixed lubrication such that the displacement is at most equal to the mean asperity height. Only normal load is involved in the solution of asperity deformation, and the mean film thickness is determined based on a total volume conservation hypothesis, in conjunction with an elastic-exponential hardening model. The singularity problem, present in the expected form of the Reynolds equation for a seal surface with circumferentially-oriented roughness grain sphere grooves, is avoided by viewing the seal roughness as porous material, thereby introducing roughness permeability. Flow permeability is thus obtained by combining Darcy’s law for porous material with the average flow model developed by Patir and Cheng for mixed lubrication. The hydrodynamic pressure and thereby the hydrodynamic load support are relatively higher from a seal with radially-oriented roughness. Both the mean film thickness and the hydrodynamic load support are substantially elevated by increasing the composite rms roughness, raising the inlet-flow pressure, and decreasing the rotational speed. Good agreement has been obtained from the comparison between the results herein and Lebeck’s experimental results.
Solutions for the Combined Motion of Finite Length Squeeze Film
Dampers Around the Bearing Center
Authors: Zhang J. X. , Roberts J. B. 
Published: February 2008

Abstract
Analytical expressions for the hydrodynamic forces, and four related dynamic coefficients, are presented for finite length squeeze film dampers (SFDs) executing combined radial and tangential motion around the bearing center, with small amplitude. Previous analyses by Mulcahy (1980) and San Andres and Vance (1987) are shown to be particular cases of the present treatment. The influence of combined motion on the coefficients is found to differ, in several respects, from that which can be deduced from results for one dimensional radial motion and circular centred orbital motion. The effects of combined motion on the mean flow velocity and the wall stress are also studied. The study provides further insight into the validity of bulk flow assumptions, often used when dealing with lubrication problems where fluid inertia effects are significant.
A Numerical Analysis of the Nonsteady EHL Process in High-Speed
Rotating Engine Cam/Tappet Pairs
Authors: Xuesong Mei , Youbai Xie 
Published: February 2008

Abstract
In this paper, by accounting for the effect of dynamic behavior in valve train mechanisms on the surface contact load of a cam/tappet pair, a full numerical solution of nonsteady EHL for a high-speed diesel engine cam/tappet pair is obtained by a fast solution scheme. The shape of the lubricant film and the characteristics of pressure distribution on cam/tappet pair surfaces are further studied. The lubrication process of a cam/tappet pair at the opening and closing sides and in the most dangerous zone in normal working conditions is also analyzed. This analysis provides the theoretical basis which best approximates practical working conditions for designing cam profiles and establishing reasonable running-in condition.
Scuffing as Evaluated From the Viewpoint of Surface Roughness and
Friction Energy
Authors: Horng Jeng Haur , Lin Jen Fin , Li Ke Yang 
Published: February 2008

Abstract
The surface scuffing occurring in line-contact lubrication is related to the roller’s roughness pattern and asperity height. For surfaces with same contact asperity height, the magnitudes of friction power (Pf = fWVs) relevant to various roughness patterns are found to have the same sequence as the critical local temperatures. Instead of using the nominal contact area, the real contact area (At) is used to obtain the true friction power intensity (Ptfi = Pf/At). A new scuffing failure model (Ptfi · σ−0.317 = C, where σ denote rms roughness) shows that the scuffing resistance of surfaces with transverse roughness pattern is higher than that of surfaces with longitudinal and oblique patterns. For certain roughness patterns, a high root mean square roughness height a is always associated with the high Ptfi value just before scuffing.
FEM Simulation of Friction Testing Method Based on Combined Forward
Rod-Backward Can Extrusion
Authors: Nakamura Tamotsu , Bay Niels , Zhang Zhi-Liang 
Published: February 2008

Abstract
A new friction testing method by combined forward rod-backward can extrusion is proposed in order to evaluate frictional characteristics of lubricants in forging processes. By this method the friction coefficient μ and the friction factor m can be estimated along the container wall and the conical die surface in the forward rod extrusion using theoretical calibration diagrams representing the relationship between the punch travel, the forward rod extrusion length and form without requirements of measuring the forming forces and the flow stress of the workpiece. The theoretical calibration curves are obtained by rigid-plastic FEM simulations in a combined forward rod-backward can extrusion process for a reduction in area Rb, = 25, 50 and 70 percent in the backward can extrusion. It is confirmed that the friction factor mp on the punch nose in the backward can extrusion has almost no influence on the calibration curves. The optimum initial height/diameter ratio of the workpiece is 1.0–1.1. The influence of the workhardening index on the calibration curves is insignificant in the range 0.1 ≤ n ≤ 0.5. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm the analysis resulting in reasonable values for the friction coefficient and the friction factor.
An Application of Self-Tuning Fuzzy Controller to Dynamic Positioning
System of Floating Production System
Authors: Inoue Y. , Du J. 
Published: February 2008

Abstract
Position-keeping of a floating body is a very important matter in a production system in the deep sea. How a floating body can be kept stationary is a key problem in this study. Conventionally, the mooring system is adopted to position a floating body under disturbance of wind, wave, and current; but, in general, it is difficult to survive storm disturbance in the deep sea. The dynamic positioning system can solve this problem, but thrusters must be operated at all times against random drift force of wave, wind, and current, and a great deal of energy is required. So a composite system of single-point mooring system and fuzzy control dynamic positioning (FDP) system was studied in a previous paper (Inoue, 1994). However, up to now in almost all kinds of dynamic positioning systems, control strategy must be decided in advance. This is unreasonable under a random condition. In this paper, a self-tuning fuzzy control system is put forward. By this approach, the control precision of the previous fuzzy dynamic positioning is fairly improved. The main concept of this approach is that at first a feasible control strategy is decided in advance, then during the motion of the system, the control strategy is improved automatically according to the sea conditions of operation. This system is more reasonable than the previous system because, in fact, the disturbance of wave, current, and wind cannot be predicted.
Wave Diffraction Around Three-Dimensional Bodies in a
Current
Authors: Cheung K. F. , Isaacson M. , Lee J. W. 
Published: February 2008

Abstract
The effects of a collinear current on the diffraction of regular waves around three-dimensional surface-piercing bodies are examined. With the current speed assumed to be small, the boundary-value problem is separated into a steady current problem with a rigid wall condition applied at the still water level and a linear wave propagation problem in the resulting current field. The boundary conditions of the wave propagation problem are satisfied by a time-stepping procedure and the field solution is obtained by an integral equation method. Free surface profiles, runup, and wave forces are described for a vertical circular cylinder in combined waves and a current. The current is shown to affect significantly the steady drift force and runup predictions. Comparisons of the computed wave forces are made with a previous numerical solution involving a semi-immersed sphere in deep water, and indicate good agreement.
Second-Order Vertical Diffraction Forces on Truncated
Cylinders
Authors: Weggel D. C. , Roesset J. M. , Kim M.-H. 
Published: February 2008

Abstract
A number of parametric studies were performed on a series of single, truncated cylinders in deep water using second-order potential theory. The cylinders were subjected to a monochromatic incident wave field. Second-order vertical diffraction force components were computed and plotted to illustrate their variation with cylinder aspect ratio and incident wave frequency. These plots make it possible to obtain rough estimates of vertical second-order diffraction force quantities on cylindrical components without having to perform second-order diffraction theory computations. The double-frequency heave response amplitude operator RAO(2) for a freely floating truncated cylinder is presented as a function of cylinder aspect ratio and incident wave frequency. Calculations of the RAO(2) were made using the total double-frequency diffraction force and the first-order radiation coefficients evaluated at the double-frequency.
Peak Response Statistics of Vertical Cylinders in Two-Dimensional
Irregular Waves
Authors: Haritos N. 
Published: February 2008

Abstract
When dealing with the probabilistic estimation of the peak response of an offshore structure dynamically responding under excitation by unidirectional irregular waves, it becomes apparent that nonlinearities introduced by the wave-structure interaction, and principally associated with the drag contribution of the Morison force model that has been traditionally used to describe this forcing, leads to non-Gaussian statistical properties of not only the forcing, but also the response. However, it is also apparent that for lightly damped structures, the response under certain circumstances can be very “narrow-banded,” and hence its statistical description would then approach the Gaussian form irrespective of whether the forcing associated with the response is itself highly non-Gaussian or otherwise. This paper treats both a numerical and experimental investigation of the peak response characteristics of compliant bottom-pivoted surface-piercing cylinders subjected to hydrodynamic excitation by unidirectional Pierson-Moskowitz (P-M) irregular waves and modeled as single-degree-of-freedom (SDOF) oscillators with a fixed “straight line” mode shape (the result of the bottom-pivoted support condition). Conditions under which the response can reasonably be approximated as Gaussian are identified via an upcrossing investigation for the likely peak response in a storm of a nominated period of duration.
Statistical Uncertainty in Long-Term Distributions of Significant
Wave Height
Authors: Guedes Soares C. , Henriques A. C. 
Published: February 2008

Abstract
This work examines some aspects involved in the estimation of the parameters of the probability distribution of significant wave height, in particular the homogeneity of the data sets and the statistical methods of fitting a distribution to data. More homogeneous data sets are organized by collecting the data on a monthly basis and by separating the simple sea states from the combined ones. A three-parameter Weibull distribution is fitted to the data. The parameters of the fitted distribution are estimated by the methods of maximum likelihood, of regression, and of the moments. The uncertainty involved in estimating the probability distribution with the three methods is compared with the one that results from using more homogeneous data sets, and it is concluded that the uncertainty involved in the fitting procedure can be more significant unless the method of moments is not considered.
Crack Arrest Toughness of a Heat-Affected Zone Containing Local
Brittle Zones
Authors: Malik L. , Pussegoda L. N. , Graville B. A. , Tyson W. R. 
Published: February 2008

Abstract
The awareness of the presence of local brittle zones (LBZs) in the heat-affected zone (HAZ) of welds has led to the requirements for minimum initiation (CTOD) toughness for the HAZ for critical applications (API RP 2Z, CSA S473). Such an approach, however, is expensive to implement and limits the number of potential steel suppliers. A fracture control philosophy that is proposed to be an attractive alternative for heat-affected zones containing LBZs is the prevention of crack propagation rather than of crack initiation. Such an approach would be viable if it could be demonstrated that cracks initiated in the LBZs will be arrested without causing catastrophic failure, notwithstanding the low initiation (CTOD) toughness resulting from the presence of LBZs. Unstable propagation of a crack initiating from an LBZ requires the rupture of tougher microstructural regions surrounding the LBZ in HAZ, and therefore the CTOD value reflecting the presence of LBZ is unlikely to provide a true indication of the potential for fast fracture along the heat-affected zone. Base metal specifications (CSA S473) usually ensure that small unstable cracks propagating from the weld zone into the base metal would be arrested. Past work has also shown that unstable crack initiation resulting from interaction of surface semi-elliptical cracks parallel to the fusion boundary with the local brittle zones can get arrested once the crack has popped through the depth of the LBZ. However, the potential for arrest when a through-thickness HAZ crack runs parallel to the fusion boundary, and thus parallel to the LBZs, has not been examined previously. To investigate the likelihood of fast fracture within the HAZ, a test program has been carried out that involved performing compact plane strain (ASTM E1221) and plane stress crack arrest tests on a heataffected zone that contained LBZs, and thus exhibited unacceptable low CTOD toughness for resistance to brittle fracture initiation. The results indicated that in contrast to the initiation toughness (CTOD toughness), the crack arrest toughness was little influenced by the presence of local brittle zones. Instead, the superior toughness of the larger proportion of finer-grain HAZ surrounding the LBZ present along the crack path has a greater influence on the crack arrest toughness. It further seems that there may be potential to estimate the HAZ crack arrest toughness from more conventional smaller-scale laboratory tests, such as conventional or precracked instrumented Charpy impact tests.
Effect of Intermittent Contact on the Stability of Thermoelastic
Sliding Contact
Authors: Ruiz Ayala Jose R. , Lee Kwangjin , Rahman Mujibur , Barber J. R. 
Published: February 2008

Abstract
In many sliding systems, the sliding surfaces are not coextensive, so that points on one surface experience alternating periods of contact and separation. This intermittent process can be expected to influence the sliding speed at which the system is susceptible to frictionally-induced thermoelastic instability (TEI). This question is explored in the context of a simple system consisting of a rotating thin-walled cylinder whose end face slides against a rigid surface. The results show that at low Fourier number—i.e., when the frequency of the process is high compared with the thermal transient of the system—only the time-averaged frictional heat input is important and the critical speed is an inverse linear function of the proportion of time in sliding contact. At higher Fourier number, lower critical speeds are obtained, but the dependence on Fourier number is relatively weak.
Finite Element Modeling of Engagement of Rough and Grooved Wet
Clutches
Authors: Berger E. J. , Sadeghi F. , Krousgrill C. M. 
Published: February 2008

Abstract
A finite element model has been developed to investigate the engagement of rough, grooved, paper-based permeable wet clutches. The finite element (Galerkin) approach was used to discretize the modified Reynolds and force balance equations, and the solution domain geometry was described using an isoparametric formulation. Surface roughness effects were modeled via the Patir and Cheng (1978) average flow model, while asperity load sharing was calculated using the Greenwood and Williamson (1966) approach. The finite element model developed, was used to investigate the effects of applied load, friction material permeability, and groove size on the engagement characteristics of wet clutches (i.e., torque, pressure, engagement time, and film thickness). The results indicate that the applied load, friction material permeability, and groove width significantly influence the engagement characteristics. Higher facing pressures increase peak torque and decrease engagement time. Higher permeability of the friction material significantly decreases engagement time but dramatically increases peak torque. Wider grooves decrease the peak torque and increase the engagement time. Groove depth does not significantly affect engagement characteristics for this model.
Rolling/Sliding of a Vibrating Elastic Body on an Elastic
Substrate
Authors: Spector A. A. , Batra R. C. 
Published: February 2008

Abstract
The rolling/sliding in the presence of friction of a vibrating elastic body on an elastic substrate is studied. It is shown that the longitudinal components of the velocity of the center of mass of the body and of the resultant frictional force are not affected by the vibration process. However, the normal vibration of the body influences the slip velocities and the distribution of frictional forces. For the problem of a harmonically oscillating long cylinder rolling/sliding on the flat surface of an elastic substrate, the time histories of the width of the contact zone and the length of adhesion subzone are computed. It is shown that the local frictional forces and slip velocities oscillate, and that the set of admissible values of the external frictional forces and moments providing the rolling/sliding regime is smaller under conditions of normal vibrations than that when the cylinder does not vibrate.
Numerical Analysis of the Influence of Waviness on the Film Thickness
of a Circular EHL Contact
Authors: Venner C. H. , Lubrecht A. A. 
Published: February 2008

Abstract
Surface roughness and/or surface imperfections are well known to significantly affect the performance of concentrated contacts. Any deviation from the smooth surface will act as a stress raiser for itself (bump) or of its neighborhood (dent), and will therefore reduce the fatigue life of the component it is part of. These imperfections can also act as initiation sites of other types of contact failure such as scuffing, when contact conditions such as load, speed and film thickness become more and more severe. With the help of increasing computer speeds and more efficient numerical techniques, a theoretical analysis of the failure of concentrated contacts becomes possible. The full answer will involve many aspects of the contact, including the generation of heat, thermal response of the lubricant and solids, non-Newtonian as well as surface chemistry effects. This paper concentrates on the way the lubricant film thickness is affected by waviness and tries to identify the locations and the conditions where the film thickness is minimal. The lubrication of nonsmooth surfaces is a transient two-dimensional problem, which will be treated without any geometrical simplification. More precisely, this paper focuses on the influence of rolling speed and the slide-to-roll ratio on the film thickness separating a smooth surface and one with transverse waviness.