bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillating Flow About Smooth and Rough Cylinders
Authors: Sarpkaya Turgut
Published: November 2009

The lift, drag, and inertia coefficients and the first ten harmonics of the lift force have been determined through the use of four smooth, four sand-roughened, and one marine-roughened cylinders. The length-to-diameter ratio of the smooth and sand-roughened cylinders was kept constant (L/D = 2) in order to determine the effect of coherence length on the force coefficients. The Keulegan-Carpenter number ranged from about 1 to 60 and the Reynolds number from about 2500 to 800,000. The results have shown that (i) the smooth cylinder data agree quite well with those presented by Sarpkaya [1, 2] and Rodenbusch and Gutierrez [3]; (ii) the drag and inertia coefficients for rough cylinders (k/D = 1/50) become independent of β (= D2/vT) or of the Reynolds number (Re = UmD/v) for β larger than about 4000; (iii) the rough-cylinder data agree quite well within those reported by Sarpkaya [2] and show that the effect of roughness is indeed very profound; and (iv) the rough-cylinder drag-coefficient data of Rodenbusch and Gutierrez [3] are somewhat larger than those obtained in the present investigation.
Second-Order Diffraction Loads on Plural Vertical Cylinder With Arbitrary Cross Sections
Authors: Masuda K. , Kato W. , Ishizuka H.
Published: November 2009

The purpose of the present study is development of a powerful numerical method for calculating second-order diffraction loads on plural vertical cylinder with arbitrary cross sections. According to the present method, second-order wave force can be obtained from a linear radiation potential without solving second-order boundary value problem. The boundary value problem for the radiation potential is solved with the hybrid boundary element method. The computations for circular and rectangular cylinders were carried out and compared with the experiments. In addition, second-order wave forces on twin circular cylinder are calculated with the present method.
The Dynamics of Marine Vehicles With Inflectional Righting Moment Curves
Authors: Patel M. H. , Witz J. A.
Published: November 2009

This paper investigates modifications to the dynamics of a marine vehicle caused by a point of inflection in its hydrostatic righting moment curve. Such inflections are shown to yield multiple equilibrium angles due to static over turning moments and to the occurrence of a classical fold catastrophe. Both frequency domain analyses and numerical solutions of the equation of roll motion are used to evaluate the influence of such inflections on the vessel’s dynamics. The analyses demonstrate that inflectional righting moment curves can yield unexpected roll amplitude jump phenomena close to resonance. The paper concludes with a discussion of the effects of such behavior on vessel hull designs.
Nonlinear Response of a Dynamic System due to Oscillatory Flow
Authors: Huang Y. M. , Krousgrill C. M. , Bajaj A. K.
Published: November 2009

The dynamic response of a structure exhibiting nonlinear stiffness characteristics and excited by a nonzero mean oscillatory fluid flow is investigated. Both the method of averaging and a multi-frequency incremental harmonic balance approach are used in understanding the primary and secondary resonances in the response. Several parameter studies are presented where the results of these two methods are compared with those obtained by numerical integration and are discussed in detail. The results point to the need for a multi-frequency solution formulation for accurate representation of the response offset and to the difficulties of using the standard method of averaging formulation for investigation of secondary resonances in the response of this system.
Analysis of Buckle Initiation in Damaged Subsea Pipelines
Authors: Tam C. K. W. , Croll J. G. A.
Published: November 2009

A rigid, perfectly plastic mechanism analysis, embodying interactive uniaxial membrane and bending plasticity, is used to predict the form of localized impact damage for tubulars. An extension of the model allows the pressure response of a pipe containing damage, and in particular the pressure at which buckling is initiated in a damaged pipeline. Test results are shown to confirm the validity of the mechanistic approach employed in predicting the damage process, while initiation tests based on a different initial imperfection configuration are shown to reproduce the trend of predicted initiation pressures. An attempt to improve the buckle performance through the use of spirally rib-reinforced pipelines is also described. Although propagation pressure buckle resistance is considerably enhanced, use of rib-reinforced pipelines is shown to have a less dramatic beneficial influence upon buckle initiation pressures.
The Stress Analysis and Experimental Research of Tubular K-Joints With Overlap
Authors: Chen Tie-yun , Chen Wei-min
Published: November 2009

The geometry of overlapping tubular joints, the equations of intersection curves and the coordinate of the intersection point are introduced first. The variational method for simple tubular joints is extended to the stress analysis of tubular K-joints with overlap. The computer program is compiled. The stress concentration factor and the position of the hot spot of an overlapping joint are found. For the sake of proving the feasibility of our analysis and program, the computed results are compared with experimental data of our photoelastic experiment and other experiments.
Coefficients of Friction of Sea Ice on Beach Gravel
Authors: Shapiro L. H. , Metzner R. C.
Published: November 2009

The coefficients of static and kinetic friction of sea ice on unfrozen beach gravel were calculated from measurements made while dragging two large blocks of sea ice (approximate weights 23,300 and 26,400 lb (10,600 and 12,000 kg)) in short increments up a sloping beach surface. The results of 36 separate experiments yielded values of the coefficients in static and kinetic friction of μs = 0.50 and μk = 0.39, respectively. These values should be applicable to calculations of the forces required to drive an ice sheet on shore during an ice push event.
The Borehole Jack—Is It a Useful Arctic Tool?
Authors: Sinha Nirmal K.
Published: November 2009

As the working temperatures in ice are very close to its melting point, it behaves viscoelastically and experiences what is commonly known as high temperature embrittlement. Its mechanical properties are rate sensitive and analysis must include load and displacement history. Borehole jack tests can be improved by the use of an electrohydraulic pump in conjunction with simultaneous recording of pressure and diametral displacement as a function of time. These small but significant modifications in the test procedures permit analysis of the response of a borehole jack test system under operational conditions in the High Arctic in first-year and multi-year sea ice.
Nonlinear Analysis of Flexible Risers Using Hybrid Finite
Elements
Authors: McNamara J. F. , O’Brien P. J. , Gilroy S. G.
Published: November 2009

A method is developed for the static and dynamic analysis of flexible risers and pipelines in the offshore environment under conditions of arbitrarily large motions due to wave loading and vessel movements. A mixed finite element formulation is adopted where the axial force is independently interpolated and only combined with the corresponding axial displacements via a Lagrangian constraint. An advantage of the resulting hybrid beam element is that it may be applied to offshore components varying from mooring lines or cables to pipelines with finite bending stiffnesses. Results are presented for the motions and forces on a flexible riser connecting a tanker to a subsea tower and also on a combined flexible riser and subsea support buoy structure which is part of a floating offshore production system.
The Onset of Chaotic Motions of a Moored
Semi-Submersible
Authors: Bishop S. R. , Virgin L. N.
Published: November 2009

This paper describes a combined numerical and geometric approach to study the dynamic behavior of a moored semi-submersible based on solutions of the nonlinear differential equation used to model the system. Complex features including competing steady states, subharmonic resonances and chaos are shown to be typical responses in regular seas. A qualitative overview is used to classify the computer data generated from direct time simulation with the aim of illustrating the inadequacies and limitations of a linear or a purely analytical approach.
Measured Accelerations on Free-Fall Lifeboats
Authors: Nelson J. K. , Hirsch T. J. , Magill J. M.
Published: November 2009

During the emergency evacuation of offshore vessels and facilities, free-fall lifeboats represent an improvement in safety over conventional lifeboat systems. Many lifeboat accidents occur during and after lowering into rough seas. If the vessel is listing much, some of the lifeboats may be unusable. The free-fall concept overcomes these problems by allowing the lifeboat to slide down an inclined ramp and fall freely into the sea away from the parent vessel. The free fall provides kinetic energy that is used to propel the lifeboat away from danger after it has entered the water. This paper discusses the measured accelerations at the occupant seats during 28-m free falls at three different launch angles. The accelerations were measured on the full-scale prototype of a current free-fall lifeboat design. Included in this paper are the procedures used to measure and interpret the acceleration data and suggested limits on human tolerance to acceleration.
Nonlinear Marine Structures With Random Excitation
Authors: Jefferys E. R.
Published: November 2009

Various important types of offshore structure contain significant nonlinearities or time-varying coefficients in their equations of motion. Well-known examples include tension leg platforms, free-hanging risers, single-buoy moorings, ships moored against fenders and vessels constrained by stiffening moorings. When subject to sinusoidal wave excitation, time domain mathematical models of these structures can display large subharmonic or chaotic motions. This paper shows that such behavior is often an artifact of the regularity of the excitation and is usually unlikely to present a significant problem in a random sea. Narrow-band vessel response can, however, generate near-harmonic motions to create conditions in which these instabilities may become important.
Motions of OTEC Platform in Waves and Forces on Mooring Chain and
Cold Water Pipe
Authors: Koterayama W. , Nakamura M. , Kyozuka Y. , Ohkusu M. , Suhara T.
Published: November 2009

The effects of hydrodynamic forces acting on the cold water pipe and mooring lines on motions of the OTEC platform are investigated experimentally and theoretically. The hydrodynamic forces acting on the cold water pipe and mooring chains oscillating in water are obtained by using mode methods. The computer time needed for the calculations is very short; therefore, the methods proposed in this paper are of great practical use. Calculated results of the bending moment and shearing force of the cold water pipe at its upper end and the horizontal and vertical components of the dynamic tension of the mooring chain at the mooring point are compared with those of experiments. They are in good agreement. Experiments and theoretical calculations on the motions of the moored OTEC platform show that the viscous drag forces acting on the cold water pipe and mooring chains have a great effect on the motion at its resonant period. They act as the viscous damping force for the motion of the platform at its resonant period, and reduce its magnification factor.
Vortex-Excited Response of Large-Scale Cylinders in Sheared
Flow
Authors: Humphries J. A. , Walker D. H.
Published: November 2009

A series of experiments were performed to measure the vortex-excited response of a 0.168-m-dia slender circular cylinder in a range of linear shear velocity profiles. Reynolds numbers of up to 2.5 × 105 were achieved. The results clearly showed that regular large-amplitude cylinder vibrations occurred well within the critical drag transition region. It was found that increasing the linear shear profile decreased the peak amplitude response but broadened the range of lock-on over which large oscillations occurred. The flow-induced vibration of the cylinder caused amplification of the mean hydrodynamic drag forces acting on the cylinder when compared with those expected for a similar rigid cylinder.
Free-Form Plate Modeling Using Offset Surfaces
Authors: Patrikalakis N. M. , Prakash P. V.
Published: November 2009

This paper addresses the representation of plates within the framework of the Boundary Representation method in a Solid Modeling environment. Plates are defined as the volume bounded by a progenitor surface, its offset surface and other, possibly ruled surfaces for the sides. Offset surfaces of polynomial parametric surfaces cannot be represented exactly within the same class of functions describing the progenitor surface. Therefore, if the offset surface is to be represented in the same form as the progenitor surface, approximation is required. A method of approximation relevant to non-uniform rational parametric B-spline surfaces is described. The method employs the properties of the control polyhedron and a recently developed subdivision algorithm to satisfy a certain accuracy criterion. Representative examples are given which illustrate the efficiency and robustness of the proposed method.
Confined Compressive Strength of Multi-Year Pressure Ridge Sea Ice
Samples
Authors: Cox G. F. N. , Richter-Menge J. A.
Published: November 2009

Fifty-five constant-strain-rate triaxial tests were performed on verticaly oriented multi-year pressure ridge samples from the Beaufort Sea. The tests were performed on a closed-loop electrohydraulic testing machine at two nominal strain rates (10−5 and 10−3 s−1) and two temperatures (−20° and −5°C). In all of the tests the confining pressure was ramped in constant proportion to the applied axial stress (σ1 > σ2 = σ3, σ3/σ1 = constant). Two σ3/σ1 ratios were investigated: 0.25 and 0.50. This paper summarizes the sample preparation and testing techniques used in this investigation and presents data on the confined compressive strength and failure strain of the ice. Uniaxial data are also included for comparison.
A Wave-Free Floating Body in Swaying Oscillation
Authors: Yamashita S.
Published: November 2009

This paper deals with the two-dimensional wave-free floating body which generates no radiating waves at a certain frequency when oscillating horizontally on the free water surface. In order to find the characteristic features of the wave-free form, the streamlines are calculated for the wave-free potential. Two kinds of wave-free bodies are given. The one is a floating body, the surface of which is inclined inwardly just below the free water surface, and the other is a fully submerged body. Numerical computations and experimental measurements of the sway exciting forces in waves are carried out for the wave-free bodies and the existence of the wave-free frequency for swaying oscillation is verified experimentally as well as theoretically. Measurements of the motions in waves are also performed on the inwardly inclined floating body that has mainly rectangular cross section. The experimental results are compared with those of the box-shaped floating body.
Dynamic Analysis and Fatigue Control of the HYLIGHT Deepwater
Platform
Authors: Thuestad T. C. , Folleso S. , Haughovd J.
Published: November 2009

The paper discusses results from a detailed stochastic dynamic fatigue analysis of a new deepwater platform concept designed for North Sea conditions. The platform concept, developed by Norsk Hydro a.s., is a fixed steel structure in a water depth of 335 m and with a deck load capacity of 35000 tonnes. The platform substructure, shown in Fig. 1, is a tripod trusswork design consisting of a central triangle tower connected to three inclined legs at elevation 45 m below the still water level. The fundamental structural natural period is in the range of 4 to 5 s, indicating significant dynamic amplification of the quasi-static wave-induced response, and fatigue will be an important design consideration. Parameters governing the fatigue life of the structure are identified and the fatigue sensitivity to these parameters is investigated. The results indicate that fatigue is important for structural elements in and above the intersection area between the main tower and the inclined legs. Important parameters governing the fatigue life are found to be the damping value, geometric stress effects, dynamic amplification, structural geometry at waterline, wave load modeling and method used for linearization of nonlinear wave forces.
The Use of Robotics and Expert Systems for the Manufacture of
Structural Beams
Authors: Gursoz E. L. , Prinz F. B.
Published: November 2009

This paper describes an expert system for a class of automated cutting operations which are of practical use in the offshore manufacturing industry. These operations include plasma cutting, oxy-fuel cutting, laser cutting and water-jet cutting. The common features in these processes, which define this class of cutting operations, are: 1) the work material is cut by the sweeping action of a line segment; 2) the cutting effect terminates at an imprecise point along the cutting segment; 3) the cutting task at hand can be fully described by the surface-boundary representation of the workpiece and the surface to be cut. The fundamental problem in such a planning task is that neither a strictly geometrical analysis, nor a purely heuristic approach is sufficient when considered alone. In this paper, we present a knowledge-based system which blends heuristics with spatial reasoning within the framework of a solid modeling system.
Sensitivity of Wave Drift Damping Coefficient Predictions to the
Hydrodynamic Analysis Models Used in the Added Resistance Gradient
Method
Authors: Hearn G. E. , Tong K. C. , Lau S. M.
Published: November 2009

This paper is concerned with the formulation and simplifications of the general fluid structure interaction analysis for an advancing oscillating vessel in waves to provide alternative 3D hydrodynamic models to determine first and second-order wave-induced fluid loadings, and, hence, the prediction of low-frequency wave damping coefficients. Heuristic arguments which lead to the Added Resistance Gradient (ARG) method of calculating low-frequency damping coefficients together with two 3D-based calculation procedures are presented. Predictions of added resistance and motion responses are compared with other published data. The intermediate hydrodynamic coefficient predictions based on 2D and 3D hydrodynamic models are compared. Low-frequency damping coefficient predictions based on the two proposed 3D calculation procedures are compared with experimental measurements and earlier published generalized strip theory values. Assessment of the applicability of the procedures, the result of their application, and further possible generalizations of the methods are discussed.
On the Increased Damping of a Moored Body During Low-Frequency
Motions in Waves
Authors: Nakamura S. , Saito K. , Takagi M.
Published: November 2009

An estimation method for the increased damping on a moored body in waves which allow simulation of the decay increase of low-frequency motion in waves is described. Emphasis is put on the analytical estimation method for the increased damping due to waves (wave drift damping) on a moored body during low-frequency motion. The estimated increased damping is compared with that of free oscillation tests in waves, and it is shown that the estimation method presented herein is acceptable qualitatively. The low-frequency resonant sway motions of a two-dimensional moored body in regular wave groups are also compared, and the numerical results show a tendency similar to the experiments when the wave drift damping is included in the equation of motion.
Three-Dimensional Scour Below Pipelines
Authors: Fredsøe J. , Hansen E. A. , Mao Y. , Sumer B. M.
Published: November 2009

This paper deals with the scour below pipelines exposed to a current. In a typical field situation, the scour pattern along a pipeline is not uniform; the scour holes are interrupted with the reaches where the pipeline is partially or totally buried. This paper focuses on the longitudinal extent of the individual scour holes. A simplified picture of the process is given to describe the longitudinal dimension of a scour hole. The sagging of the pipeline is an essential element of the process. The effect of sagging on the final scour depth is investigated, using a two-dimensional laboratory model. A simple equation to calculate the length of individual scour holes (the span length) is developed. The practical application of the equation is demonstrated by an example.
A Numerical Procedure for Vehicle-Induced Internal
Waves
Authors: Suh I. , Hires R. I.
Published: November 2009

An axially marching numerical method is developed for the simulation of the internal waves produced by the translation of a submersed vehicle in a density-stratified ocean. The method provides for the direct solution of the primitive variables [v, p, ρ] for the nonlinear and steady-state three-dimensional Euler’s equation with a nonconstant density term in the vehicle-fixed cartesian coordinate system. By utilizing a known potential flow around the vehicle for an estimate of the axial velocity gradient, the present parabolic algorithm allows local upstream disturbances and an axial velocity variation.
Transverse Vibrations of an Elastically Mounted Cylinder Exposed to
an Oscillating Flow
Authors: Sumer B. M. , Fredsøe J.
Published: November 2009

This study reports the results of an experimental work carried out with an elastically mounted rigid cylinder exposed to an oscillating flow. To facilitate comparison, the steady current case is included in the test program as well. The oscillatory flow as well as the steady current conditions are created by the so-called carriage technique. The present study covers the Keulegan-Carpenter number range 5 ≤ KC ≤ 100. The range of the reduced velocity is from 0 to approximately 16 in most of the cases. The tests have been conducted for different combinations of spring stiffness and mass of cylinder. The present results shed considerable light into the understanding of the various vibrational response patterns obtained for different ranges of KC number. The response characteristics of the cylinder have been shown to vary extensively, depending on Keulegan-Carpenter number as well as on the reduced velocity.
Mechanical Properties of Antarctic Sea Ice
Authors: Urabe N. , Inoue M.
Published: November 2009

Ice samples were extracted from a land-fast ice sheet of 90 cm thickness at Lutzow-Holm Bay in the Antarctica. The ice samples were then shipped to a cold room in Tokyo, and unconfined uniaxial compression tests and fracture toughness tests were performed for a wide range of loading rate under temperature varying from −5°C to −30°C. During the tests limited in number, acoustic emission measurements were also carried out. On the other hand, distributions of salinity, density, air content, fabric structure and grain size were examined along the thickness direction of the ice sheet. The ice sheet consisted of fine-grained granular ice at the top surface layer and columnar grains below it. The grain size was less than 1 mm for the granular ice and the columnar ice grain size increased linearly with the depth from about 1 mm just beneath the transition zone to about 13 mm at the bottom surface. The density and the air content also varied showing its maximum or minimum value, respectively, at the mid-thickness position along the thickness direction of the ice sheet. Thus, correlations between the mechanical properties and the physical features were studied. The fracture toughness (KIC) of the columnar grained ice showed a strong dependence on the grain size (diameter of the columnar ice). Namely, the KIC decreased in proportion to the inverse square root of the grain size. The compressive strength showed a linear relationship with the density, which was a function of not only the brine volume, but also the air content. Accordingly, the compressive strength was recognized to decrease with an increase in the sum of the square root of brine volume and the square root of air content. The other ice samples were also extracted from one of icebergs in Lutzow-Holm Bay. And the compressive strength and the fracture toughness were measured and reported in this paper.
Reference Strength of Ice to be Used in Designing Offshore
Structures
Authors: Tunik A. L.
Published: November 2009

The strength of ice depends on many factors. If they are known, the strength can be predicted with an acceptable accuracy. When designing an offshore structure, a designer usually has to select appropriate values of ice strength from incomplete, uncertain and random observation data for the site-specific ice environment. In this paper, a simplified method of selecting such values is described. A reference value of compressive strength is presented as an analytical function of averaged site-specific environmental parameters and offshore structure dimensions which are usually available to the designer.
The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part I—Single Irregularities
Authors: Goglia P. R. , Conry T. F. , Cusano C.
Published: November 2009

A full line contact solution, under isothermal conditions, is obtained in which the effects of single stationary surface irregularities on the EHD lubrication process are studied under pure sliding conditions. The irregularities studied are furrows, furrows with built-up edges, and asperities. The effects of these irregularities on film thickness, pressure, and subsurface octahedral shear stress are presented. The pressure and film thickness resulting from such surface irregularities are significantly changed from their smooth surface values. These changes alter the state of stress in the subsurface region by increasing the maximum value of octahedral shear stress and bringing the location of this maximum stress closer to the surface. The film thickness in the contact is significantly changed from the smooth surface value only when the irregularities are located in the inlet region while the maximum value of the octahedral shear stress increases to the greatest extent when the irregularities are located in the outlet half of the contact.
The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part II—Wavy Surfaces
Authors: Goglia P. R. , Cusano C. , Conry T. F.
Published: November 2009

The micro-EHD effects caused by wavy surfaces have been analytically investigated. The investigation includes the effects of phase, wavelength, and wave amplitude on film thickness, pressure distribution and subsurface octahedral shear stress field. The presence of a wavy surface with a given wavelength produces pressure oscillations of the same wavelength. With increasing wave amplitude and decreasing wavelength, the micro-EHD action increases. This results in a maximum value of the octahedral shear stress which is greater in magnitude and closer to the surface than the corresponding smooth surface case. The slope of the wavy surface in the inlet region determines whether the average film thickness is smaller or larger than the smooth surface value.
Transient Lubricating Films With Inertia—Turbulent Flow
Authors: Elrod H. G. , Anwar I. , Colsher R.
Published: November 2009

This paper presents some new equations for the treatment of turbulent lubricating films when the effects of inertia cannot be neglected. The eddy-viscosity concept is used to represent the turbulent stresses in terms of mean-velocity gradient. Transient and steady-state operation are both considered by means of a generalized stream-function-pressure development.
Analytical Solution for a Class of Quadrilateral Stepped Slider Bearings
Authors: Blech J. J. , Etsion I.
Published: November 2009

Analytical solution is presented for a class of quadrilateral stepped slider bearings. The solution is based on a variational method type of approximation. Results are compared with a finite difference solution to establish the range of validity of the analytical approximation. Bearings performance are presented for various aspect ratios and compared with the performance of the conventional rectangular stepped slider. A range of aspect ratios is found where the quadrilateral bearing is superior to the rectangular one.
An Adaptive Squeeze-Film Bearing
Authors: Burrows C. R. , Sahinkaya M. N. , Turkay O. S.
Published: November 2009

This paper examines the effect of controlling the oil supply pressure to squeeze-film bearings in applications where these elements are used to provide damping for a light flexible transmission shaft having an arbitrary unbalance mass distribution. The shaft length and diameter selected for the study are typical of those used for helicopter tail rotor transmissions. A computer simulation is undertaken to study the effect of a squeeze-film damper located at: 1) The end supports. 2) Mid-span with undamped end supports. 3) Mid-span with damped end supports. The simulation shows that in this type of application, good vibration control can be achieved by using a squeeze-film damper which is capable of switching between two levels of damping. The feasibility of attaining such a characteristic is examined experimentally.
On the Effect of Hydrodynamic Action on the Contact Area of Highly Loaded Line Contacts
Authors: Mokhtar M. O. A. , Abdel-Ghany A. A.
Published: November 2009

The elastically deformed contact area together with the oil film thickness between lubricated plane cylinders in relative motion are experimentally measured and analyzed under various loads and speeds. The measured contact profile has shown to be a function of the operating variables and consequently represents a justifying means in deciding the appropriate solutions to the lubrication problem in concentrated contacts. Under heavy loads and very low speeds, the deformation at the contact zone approaches the flat Hertzian contact, while at increased speeds elastohydrodynamic regimes prevail and relatively thick oil film could form with the presence of a local constriction at the trailing oil exit end. By further speeding up the local deformation diminishes and full (rigid) hydrodynamic solution would govern the lubricant oil behavior with minimum local deformations.
Effect of Slip Flow on the Steady-State Performance of Aerostatic Porous Journal Bearings
Authors: Singh K. C. , Rao N. S. , Majumdar B. C.
Published: November 2009

A theoretical solution is presented to predict the steady-state performance characteristics of aerostatic porous journal bearings of finite thickness considering three dimensional flow in the porous media. The analysis takes into account the velocity slip at the film bearing interface by using Beavers-Joseph criterion. Results are presented in dimensionless form for load capacity and mass rate of flow for different operating conditions and bearing dimensions. Solution is also obtained for modified slip velocity conditions and both the results are compared. It is observed that there is no agreement between two models except for few values of slip parameters. Hence, it is preferable to use the Beavers-Joseph model in order to account for all values of slip parameters. The effect of slip velocity on the static characteristics is discussed.
An Externally Pressurized Supersonic Gas Thrust Bearing (1st Report, Static Characteristics in Supersonic Operations)
Authors: Miyake Y. , Inaba T. , Hibi M.
Published: November 2009

A completely new type of externally pressurized gas thrust bearing is proposed and its static characteristics are analyzed. Unlike conventional gas bearings whose load capacity depends on the viscosity of gas, the load capacity of this new type of bearing is independent of the viscosity of gas since it utilizes the choking phenomenon of gas flow to maintain high pressure in the bearing clearance. Also the change of the location of the throat generates bearing stiffness. Since the flow is supersonic at the exit of the bearing clearance, the flow conditions downstream of the exit do not affect the flow inside the bearing clearance. Accordingly, the load capacity increases proportionally to the supply pressure. Thus, the main disadvantage of conventional gas bearings, namely, the deficiency of their load capacity is overcome.
An Externally Pressurized Supersonic Gas Thrust Bearing (2nd Report, Dynamic Characteristics in Supersonic Operations and Static Characteristics in Sonic Operations)
Authors: Miyake Y. , Inaba T. , Matsuoka T.
Published: November 2009

The dynamic characteristics of a newly proposed supersonic gas thrust bearing are analyzed under supersonic operations. Its static characteristics in sonic operations are also investigated. It is concluded that the load capacity, the stiffness factor, and the damping factor are increased proportionally to the supply pressure in either supersonic or sonic operation range which is determined according to the magnitude of the clearance.
Analysis of the Real Area of Contact Between a Polymeric Magnetic Medium and a Rigid Surface
Authors: Bhushan Bharat
Published: November 2009

The statistical analysis of the real area of contact proposed by Greenwood and Williamson is revisited. General and simplified equations for the mean asperity real area of contact, number of contacts, total real area of contact, and mean real pressure as a function of apparent pressure for the case of elastic junctions are presented. The critical value of the mean asperity pressure at which plastic flow starts when a polymer contacts a hard material is derived. Based on this, conditions of elastic and plastic junctions for polymers are defined by a “polymer” plasticity index, Ψp which depends on the complex modulus, Poisson’s ratio, yield strength, and surface topography. Calculations show that most dynamic contacts that occur in a computer-magnetic tape are elastic, and the predictions are supported by experimental evidence. Tape wear in computer applications is small and decreases Ψp by less than 10 percent. The theory presented here can also be applied to rigid and floppy disks.
Microdisplacements Between Two Elastic Bodies Separated by a Thin Film of Polystyrene
Authors: Tonck A. , Sabot J. , Georges J. M.
Published: November 2009

This paper describes and experimental investigation of the microdisplacements between two elastic bodies in contact under the action of a tangential force less than that of limiting friction. Experiments have been performed for the contact of 52100 steel ball with a 52100 steel flat separated by a thin film of polystyrene. Measurements of microdisplacements have been made under oscillating tangential forces of various frequencies (1 Hz to 1 KHz) and different film thicknesses (0.05 μm to 1.2 μm) were used to study the perturbations of the Mindlin’s theoretical two elastic body results. For very small tangential force (i.e., for displacements which are almost entirely elastic), the measured compliance of the present three body system is higher than the two body system studied by MINDLIN. The compliance increases noticeably with the film thickness. Furthermore, an approximate value of the elastic shear modulus of the pressurized film has been obtained. When the tangential force is greater than the elastic limits, it has been observed that the frictional energy loss per cycle in the contact area is related to the presence of the film and to its thickness.
Vickers Indentation Curves of Magnesium Oxide (MgO)
Authors: Loubet J. L. , Georges J. M. , Marchesini O. , Meille G.
Published: November 2009

Studies of Vickers hardness of magnesium oxide are presented in the literature for three purposes. They give information about relations between hardness and brittleness, (plasticity and toughness behavior); they show the anisotropical effect of the structure of the material and they are a tool to study the chemomechanical effects (Rebinder effects). Generally, the Vickers hardness is evaluated by measurements of the diagonals of residual indentation. Equipment was built which gives a record of the applied depression depth (h) as a function of the carried load P (in the range 10−1 N to 10+1 N). Investigation of the curves P(h) during loading and unloading and microscopical observations of residual indentation show that phenomena are complex. The contact is elastoplastic. The roles played by the plasticity and elasticity are discussed. The physical meaning of Vickers hardness, determined by use of residual indentation measurements, is analyzed.
Roughness-Induced Transient Loading at a Sliding Contact During Start-Up
Authors: Anand A. , Soom A.
Published: November 2009

The effects of normal contact vibrations, horizontal rider dynamics, and surface texture inputs are combined to examine dynamic loads at a contact during acceleration from rest to a steady state velocity. A constant sliding friction coefficient is assumed. The surface input is either a sine wave or a quasi-random function. The nondimensionalized system equations are solved numerically for a variety of system and input parameter combinations. The most interesting responses occur when the acceleration duration includes a number of periods of at least one of the system resonant frequencies. It would appear that surface-roughness and waviness can cause the normal motions and force fluctuations that occur during the transitions from static to sliding friction.
Interactions Among Friction, Wear, and System Stiffness—Part 1: Effect of Normal Load and System Stiffness
Authors: Aronov V. , D’Souza A. F. , Kalpakjian S. , Shareef I.
Published: November 2009

Dry frictional contact between two metallic surfaces, one cast iron and the other steel, is analyzed. The experiments were conducted using a pin-on-disk setup instrumented with force and acceleration transducers. The interactions between friction, wear, and vibrations and their dependence on normal load and system stiffness are investigated. The results indicate that stiffness has a significant effect on the normal load at which transition takes place from mild to severe friction and wear. The variation of surface roughness with normal load for different stiffnesses is also examined. The different regimes of friction are observed, as the normal load is increased. They are characterized as steady state friction region, nonlinear friction region, region of transient friction with disturbances and region of self-excited vibrations. It is shown that the transition from the steady-state friction can be characterized by a sudden increase in the coefficient of friction and amplitude of slider oscillations.
Interactions Among Friction, Wear, and System Stiffness—Part 2: Vibrations Induced by Dry Friction
Authors: Aronov V. , D’Souza A. F. , Kalpakjian S. , Shareef I.
Published: November 2009

Different types of vibrations induced by dry friction are investigated by means of a model apparatus described in Part 1. The structural model is obtained from the measurement of the modal frequencies and damping ratios of three degrees of freedom. The oscillations in the normal and frictional forces, as well as the slider vibrations, have been measured and analyzed. As the normal load is increased, four different regions of vibrations are observed corresponding to the four friction regimes discussed in a companion paper. Small oscillations are encountered at low values of the normal load and they are possibly caused by random surface irregularities. The vibration characteristics are changed when transition occurs from steady state friction. When the normal load is further increased, self-excited periodic vibrations are produced. The spectra of the oscillations are related to the modal frequencies. Self-excited vibrations are analyzed on the basis of the experimental data.
Hydrodynamic Lubrication in Simple Stretch Forming Processes
Authors: Wilson W. R. D. , Wang J. J.
Published: November 2009

Theoretical models for the hydrodynamic lubrication of plane strain and axisymmetric sheet metal stretch forming processes with cylindrical and spherical headed punches, respectively, are developed. The lubricant is treated as an isoviscous Newtonian liquid for both geometries. In addition, the influence of sheet heating due to plastic deformation with an exponential variation of viscosity with temperature is analyzed for the plane strain case.
Analysis of a Needle Bearing
Authors: Oh Kong Ping
Published: November 2009

A theory was proposed to explain the generation of side thrust in a needle bearing. A quasi-static analysis was performed, which considers the deformation and the equilibrium of the various elastic components. From this analysis, the magnitude of the thrust force can be predicted.
Subsurface Stress Evaluations Under Rolling/Sliding Contacts
Authors: Kannel J. W. , Tevaarwerk J. L.
Published: November 2009

A computer model has been developed for evaluating the subsurface stresses incurred within rolling/sliding (elastic) contacts. The model involves first defining the stress tensor at any point (x, y, or z) beneath the surface in terms of the surface stresses. The stress tensors are analyzed to determine the maximum shear stresses and stress reversals. As a result of computations with the model, several observations were made. For example, the maximum reversing shear stresses are on the plane of the orthogonal shear stress. Further, the magnitude of these stresses is not altered by friction. However, under very high friction (typical of dry contact) surface stresses can dominate over subsurface stresses.
Counterface Roughness Effect on the Dry Steady State Wear of Self-Lubricating Polyimide Composites
Authors: Play D. F.
Published: November 2009

Initial counterface topography influences both running-in and steady state wear rates of polymers. But governing roughness parameters are difficult to isolate because of their strong dependences and their statistical natures. Distributions of RT, RA, R.M.S., Skewness, Kurtosis, profile slopes, number of peaks per unit length, radii of curvature of peak asperity and Fourier transform were considered to characterize the isotropic roughness of the abraded steel disks. Two polyimide composites with PTFE and CF x powders were chosen for the pins. Correlations between parameters, friction and linear steady state wear were obtained through statistical data analysis. Radii of curvature, profile slopes or RA, and number of peaks govern friction and wear in different ways depending on fillers. However, for both materials, wear increases with average slopes or RA and decreases with an increase of number of peaks and radii of curvature. Skewness governs also the results but Kurtosis and wave length of the maximum of the Fourier transform are useless to explain the results.
Comparative Dry Wear of PTFE Liner Bearing in Cylindrical and Spherical Geometry
Authors: Play D. F. , Pruvost B.
Published: November 2009

Most fundamental laboratory studies in oscillating testing have been performed on cylindrical geometry. However, industrial applications focus generally on spherical geometry and extrapolation of results must be attempted. The same PTFE liner material with pitch structure has been considered in cylindrical and spherical geometry with oscillating amplitudes of motion and loads as study parameters. Other mechanical and thermal parameters were controlled on the two corresponding test rigs. Friction, wear, and degradations have been compared. Results have shown, particularly at small amplitudes and loads, that the geometry controls wear debris movement in the contact and explains differences in wear. Further, normal conformity or curvature difference between ball raceway and liner steel backing has been introduced.
Fretting: Load Carrying Capacity of Wear Debris
Authors: Colombie´ Ch. , Berthier Y. , Floquet A. , Vincent L. , Godet M.
Published: November 2009

Third body load carrying capacity noted with different materials under different kinematic conditions have been observed under fretting conditions. Tests run in the same machine with steel on steel, and chalk on glass, have shown similar particle shape and shape changes and similar particle motion. Observations show that third bodies formed with particles govern wear.
On the Lubrication of Rough Rollers
Authors: Prakash J.
Published: November 2009

Christensen’s stochastic model of hydrodynamic lubrication as extended to two sided roughness is used to study the effect of surface roughness in the analysis of lightly loaded rollers in combined rolling, sliding and normal motion. A detailed study of the above system in terms of dimensionless parameters, Q (involving the normal and entraining velocity, the minimum film thickness and the equivalent cylinder radius); the slide roll ratio and the surface roughness parameter is made for purely longitudinal and purely transverse surface roughness.
An Analysis of the Squeeze Film Between Rough Porous Rectangular Plates With Arbitrary Porous Wall Thickness
Authors: Prakash J. , Tiwari K.
Published: November 2009

The Christensen’s stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effects of surface roughness on the response of the squeeze film between rectangular plates when one plate has a porous facing. An exact solution, valid for arbitrary wall thickness, is obtained for the film pressure and pressure in the bearing material. A comparison is made with an earlier approximate analysis, applicable to thin porous walls to determine the range of influencing parameters for which the approximate solution is acceptable.
Fluid Inertia Effects in a Squeeze Film Between Two Plane Annuli
Authors: Elkouh A. F.
Published: November 2009

An analysis is presented for the laminar squeezing flow of a Newtonian in-compressible fluid between parallel plane annuli. Both local and convective inertia of the flow are considered in the analysis. Power series expansions in terms of pertinent flow parameters are used to obtain a solution of the equations of motion. Expressions for the pressure and load capacity are presented, and compared with those based on the assumption of inertialess flow.
An Approximate Analysis of the Temperature Conditions in a Journal Bearing. Part I: Theory
Authors: Lund J. W. , Hansen P. K.
Published: November 2009

An analysis is presented for solving the energy equation for a journal bearing film, coupled with the heat conduction equation for the bearing sleeve. The analysis approximates the temperature profile across the film thickness by a fourth order polynomial while the circumferential temperature variation is expressed in terms of a Fourier series expansion. The solution gives the temperatures of the journal, the bearing sleeve, and the lubricant film from which the viscosity distribution can be obtained for use in solving Reynold’s equation. Because the method is quite economic in computer time it should prove useful in practical calculations of journal bearing performance.
A Full Numerical Solution for the Thermoelastohydrodynamic Problem in Elliptical Contacts
Authors: Zhu Dong , Wen Shi-zhu
Published: November 2009

In this paper a full numerical solution for the thermoelastohydrodynamic problem in elliptical contacts is presented, and the method of computation is also described. The film pressure, thickness, and film shape, the three dimensional temperature distribution within both the film and the bounding solids, as well as the coefficients of the sliding and rolling frictions have all been determined for different rolling velocities and slide-roll ratios. The results obtained indicate the film temperature increases as the rolling velocity or slide-roll ratio increases. The effects of thermal action on the pressure distribution, the film shape and thickness, and the friction factors are also given. The problem studied in this paper is steady-state, the lubricant is assumed to be Newtonian.