bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Prediction of Air Gap Response of Floating Offshore Structures Using Direct Boundary Element Method
Authors: Kazemi Saeid , Incecik Atilla
Published: November 2008

The air gap response and potential deck impact of ocean structures under waves is the main topic of this research. In this paper, an analytical prediction of the air gap for floating offshore structures using direct Boundary Element Method (BEM) is presented. The main advantage of direct boundary element method is the fact that one can determine the total velocity potential directly. Direct BEM is more versatile and computationally more efficient than indirect BEM. Besides, the direct BEM can easily be coupled with other numerical methods, e.g. finite element method (FEM) in order to carry out structural analysis of the platform’s deck due to possible impact. Firstly, the direct boundary element method will be reviewed. Secondly, the boundary value problem of interaction between regular sea waves and a semi-submersible and air gap responses due to the motion of the platform and the local wave elevations (including both radiation and diffraction waves) will be described. Then, the direct boundary element method will be applied to predict of the air gap at different field points of ALBORZ semi-submersible drilling unit, which is the largest semi-submersible drilling platform under construction for a location in the Caspian Sea, North of Iran. In addition, the results obtained from the direct BEM will be compared with those obtained by the designers of the ALBORZ semi-submersible. To determine the influence of the structure’s motions on the air gap, the results for both fixed and free-floating structure cases will be compared. Physical simulations using model will be carried out in the future in order to compare the results of the experiments with predictions.
Analysis of Extreme TLP Tether Tension Amplitudes With Comparison to Model Tests
Authors: Johannessen Thomas B. , Sandvik Arild K.
Published: November 2008

The Snorre TLP has been operating in the Northern North Sea since 1992. During the last year, an extensive reanalysis of tether tension, TLP motion and airgap has been carried out in order to ensure that the TLP can withstand updated environmental conditions and design requirements. It is the object of the present paper to describe the analysis methods which have been employed to determine extreme tether loading and to compare analysis results with model test results. The model tests were carried out in the facilities at MARIN in the Netherlands and considered more than 200 three hour realizations of irregular seastates with and without wind and current. Typical fatigue seastates as well as extreme 100 year and 10 0000 year seastates were investigated for both head and quartering seas. The extensive database of model test results gives an opportunity to study the accuracy of the analysis methods. The analysis of the TLP response was carried out in the time domain using the SIMO software developed by Marintek. In the work described here, the results from a purely linear radiation-diffraction analysis is used as the main load model in SIMO together with slender element additions based on the incident wave kinematics. The slender elements give loads on tethers and risers, viscous loads on the TLP hull and also provide a simple third order load model for the excitation of high frequent response in the surface zone. SIMO has also been implemented with second order quadratic force transfer functions, but it is concluded that the second order loading does not give significant contributions to extreme tether tension. It is concluded that, at least for the Snorre TLP, the relatively simple analysis model gives good agreement with measured extreme tether tension provided that the TLP is modeled carefully. By filtering the tether tension time series, the contributions due to wave frequent and high frequent (resonant) tether tension may be separated. It is shown that the main discrepancy between model test and analysis results of tether tension lies not in the magnitude but in the simultaneity of wave frequent and high frequent tether response. If this is due to the tendency for large waves to propagate towards the front of the nonlinear wave envelope, this may be extremely difficult to capture in analysis models.
Numerical Study of Spudcan Foundation Penetrating Into Layered Soils
Authors: Mehryar Zarnaz , Hu Yuxia
Published: November 2008

Spudcan foundation, penetrating into stratified soils is studied using H-adaptive finite element method (FE) together with Remeshing and Interpolation Technique with Small Strain model (RITSS). This is to investigate the potential hazard of punch-through failure in layered soil profiles. There are two series of analysis conducted. Firstly, for a pre-embedded spudcan foundation, a series of parametric studies has been undertaken in order to find the critical distance between the spudcan and the layer boundary, within which a punch-through failure is likely to occur. Soil profile is a uniform stiff clay layer overlaying a uniform soft clay layer with soil strength ratio (upper layer soil strength to lower layer strength) varying from 1 to 10. Secondly, continuous analysis has been undertaken for 2 cases with shear strength ratio of 2 and 3 and thickness of the upper stiff layer of one spudcan diameter. It is found that, in small strain analysis, the critical distance to the layer boundary is increasing with increasing the strength ratio. It reaches at a limit of 1.0 ∼ 1.25 D (D is the spudcan diameter) when the strength ratio is 5 or larger. In large deformation analysis, the critical distance is much lower than the one from small strain analysis. This is due to the trapped top layer soil underneath the spudcan, which cannot be simulated in small strain analysis.
Unstable Response of Hanging Chains Near Resonance and the Effect of Damping in Marine Applications
Authors: Chatjigeorgiou Ioannis K.
Published: November 2008

This paper investigates the dynamic behaviour of a hanging chain for excitation frequencies that lie in the vicinity of natural frequencies. The results are validated using two different solution methodologies. The study is conducted for both the undamped and the damping included cases. The calculations concern mainly the free end of the chain as this is the point that performs the larger motions.
West Sole Pipeline Stabilisation
Authors: Chen Z. , Sheehan Eamon
Published: November 2008

The BP West Sole gas field is located in Block 48/6 in the UK sector of the southern North Sea, about 70 km off the Holderness coast. Production from the gas field is exported to a shore terminal at Easington by two pipelines. Both pipelines were trenched at installation. Pipeline surveys over the last few years show that both pipelines are substantially exposed at the shore approach and inshore sections. This has occurred in part due to the retreat of the cliffs in Easington and subsequent lowering of the sea bed level and also the migration of sand from around the pipelines leaving them largely unburied and sitting on the local clay abrasion platform. It has been concluded that both pipelines require stabilisation sooner rather than later to reduce the risk of pipeline failure. Pipeline stabilisation options need to take account of the environment in which they have been placed. Easington is at a critical position along the Holderness coast. All net sediment transport from the Holderness coastline passes through this section. Any interruption to this movement could result in a change to the adjacent coast. Maintenance of the sediment budget is important to a wider area of the East coast of England. Stabilisation options must not reduce the net amount of sediment moving southwards past Dimlington and must not result in any long term negative impact on the coastal evolution. This paper outlines consultancy required and problems process regarding the geomorphological issues in getting acceptance from government and non-government bodies. A methodology has been developed that allows quantification of impacts of different options on the sediment budget and on the long-term coastal evolution (see also Chen et al 1998, 2001 and 2002). Application of this method aimed at providing understanding and information which is considered to be important in the process of selecting an optimal solution for the pipeline stabilisation in such an environmental sensitive coast.
Design Challenges for the K2 North Project Steel Catenary Risers
Authors: Mekha Basim B. , Fang Jie , Lemker Mike
Published: November 2008

The K2 North project located in Green Canyon Block 518 (GC518) in the Gulf of Mexico ties-back four subsea oil wells to a host facility (Marco Polo TLP) in the GC 608, in approximately 4300 feet water depth. The plan is to tie-back the subsea wells via dual pipe in pipe insulated flowlines through an insulated production manifold. Each well will connect to the manifold via insulated flowlines or insulated flowline jumpers. The flowlines connect to the host facility via Steel Catenary Risers (SCRs). These SCRs consist of heavy wall 6.625-inch pipe with wet buoyant insulation necessary to minimize the impact of top tension loads on the host facility. This paper discusses the key aspects of the design of the SCRs, and highlights the importance of a prudent engineering approach to deliver the optimal riser solution. These include the early identification of the potential for interference between the two project risers, and with the third party risers and adjacent TLP tendon. This design aspect was exacerbated by the weight limit imposed on the tieback risers, and by the use of VIV suppression strakes suitable for the selected installation method. The paper describes the solutions developed to avoid interference relating to riser layout and configurations and selection of wet insulation coating system. The paper also presents the qualification tests planned and conducted to prove the suitability of the wet insulation coating system for the S-lay installation method. K2 North (GC518) risers will be the first application of this coating on SCRs. The paper also demonstrates the importance of allowing sufficient margin in early stage of design to accommodate future changes as design matures, especially for fast track projects like this one. The K2 North SCRs represent typical subsea tieback scenarios in the Gulf of Mexico. The experience gained during the engineering design of these risers is therefore of significant value with regard to assisting in safe and economic design of such future developments.
Large-Scale Free-Surface Flow Simulations Using FEM
Authors: Aliabadi Shahrouz , Watts Marvin , Johnson Andrew
Published: November 2008

A parallel finite element fluid-structure interaction free-surface solver is developed for numerical simulation of water waves interacting with floating objects. In our approach, the governing equations are the Navier-Stokes equations written for two incompressible fluids. An interface function with two distinct values serves as a marker identifying the location of the interface. The numerical method is based on writing stabilized finite element formulations in an arbitrary Lagrangian-Eulerian frame. This allows us to handle the motion of the floating objects by moving the computational nodes. In the mesh-moving schemes, we assume that the computational domain is made of elastic materials. The linear elasticity equations are solved to obtain the displacements. In order to update the position of the floating object, the nonlinear rigid body dynamics equations are coupled with the governing equations of fluids and are solved simultaneously. The mooring forces are modeled using nonlinear cables and linear spring models. The finite element formulation is implemented on Cray X1.
Behavior of a Mono-Column Structure (MonoBr) in Waves
Authors: Barreira Rodrigo , Sphaier Sergio H. , Masetti Isaias Q. , Costa Ana Paula , Levi Carlos
Published: November 2008

MonoBr is the name of a concept of a mono-column structure with a moon-pool developed by PETROBRAS to operate in deep water. A set of tests has been carried out at LabOceano / COPPE / UFRJ to analyze its behavior in waves. Different configurations of the moon-pool entrance have been tested. The main objective of the measurements carried out is to determine the influence of different restrictions on the behavior of the vertical motion of the structure. Results of these measurements are presented and discussed in the paper.
Fatigue Calculations of Multi-Mode VIV
Authors: Ilstad Trygve , So̸reide Tore , Nielsen Finn Gunnar
Published: November 2008

Pipelines on undulating seabed may be subject to free-span areas where interaction between VIV response of several modes occurs, including both single and multi-spans. Within the project Ormen Lange a model test program, as completed in 2004, was performed to investigate this phenomena. The implementation of the test results into detail design went via an Ormen Lange specific design guideline in which the general analysis flow is given. However, taking the mode interaction effects from the tests into the actual routing makes the need for additional evaluations and generalisation on dynamic system of interacting spans. A dynamic system represents a set of spans were the eigenmodes interact physically and not only mathematically in computation of the eigenmodes over a long pipeline section. For a single span case we find that the modes are well separated while for multi-span problems modes are close in frequencies. A clear criterion and limitation on dynamic system to be considered becomes vital. The relative effect of inline and cross flow VIV in actual design depends on the SN-curves at hand. The general trend is that inline generated fatigue takes over for corrosion sensitive problems covering operation phase, whereas preliminary phases may be governed by cross flow response. The modelling of pipe-soil interaction at shoulders is vital for the multi-span response characteristics, the experience being that softer soil gives minor span interaction. The soft soil gives deeper pipeline penetration and more uniform support stiffness all along the shoulder than the hard soil for which local reactions occur more like pinned supports.
Comparison on Stress Concentration Factors of Y/T Tubular Joints Between Numerical and Parametric Formulation Results
Authors: Baratella Stefano , Boote Dario , Petrillo Fabio , Stefani Fabrizio
Published: November 2008

The action of environmental loads such as wind and waves on offshore steel structures is locally emphasized by complex tubular connections, giving place to high stress concentration in correspondence of welds between pipe elements. This phenomenon, which heavily influences the fatigue life of the joint and, as a consequence, the operability of the whole platform, can be quantified by the Stress Concentration Factor. SCF can be determined either by experimental approach, numerical analysis and parametrical formulas developed mainly in the seventies-eighties by specialized authors like Kuang, Wordsworth, Smedley and Efthymiou. Even though these formulas, quoted as reference in the main world recognized rules, represented for a long time a useful tool for the designers of most projects, some discrepancies have been found to exist among them. A research has then been jointly promoted by University of Genoa and RINA Industry in order to compare the results of the parametric formulas with those coming from a finite element analysis performed on very refined numerical models made of brick elements. In this investigation attention has been focused on Y/T type joints; a wide range of configurations has been analysed by varying the most important parameters defining the geometry of the joint. Each configuration has been loaded by axial force and in/out of plane bending moment.
The Flat Solitary Waves Due to a Submerged Moving Body in a Two-Layer Fluid With a Free Surface
Authors: Wei Gang , Su Xiao-Bing , You Yun-Xiang
Published: November 2008

The flat solitary wave with the behavior of conjugate flow, generated by a submerged body moving in a two-layer fluid, is investigated. A criteria about the existence of weakly nonlinear weakly dispersive flat solitary wave is given. The condition of the stable system of conjugate flow is obtained. The solution of the flat solitary wave satisfying the criteria is numerically verified to be unique. Theoretical analysis is qualitatively consistent with the experimental results obtained by the authors.
Use of an Electro-Optical-Mechanical Mooring Cable for Oceanographic Buoys: Modeling and Validation
Authors: Hamilton Andrew , Chaffey Mark
Published: November 2008

This paper presents results of numerical modeling of an oceanographic mooring system and makes comparisons to loads measured on a deployed test mooring near Monterey Bay, California. The numerical modeling solves the non-linear equations of motion of the cable in the time-domain. The deployed system is instrumented to monitor environmental loading and the resulting tensions in the mooring cable below the buoy and above the anchor. Comparison of the numerical results to the measured results is useful to refine the accuracy of the model, allowing its use in determining fatigue life of the system and for designing similar systems to be deployed in new locations. This study is part of a project to develop and improve mooring systems for oceanographic use that include an electro-optical-mechanical mooring cable that delivers power and data communication to a network of sea-floor instrumentation. The modeling and test results highlight the engineering challenges associated with designing these systems for long lifetimes.
Fitness for Service Analysis of Structures Using the FITNET Procedure: An Overview
Authors: Koc¸ak Mustafa
Published: November 2008

A number of Fitness-for-Service (FFS) procedures (include analytical methods) have been specifically developed and used to address the components of a particular industrial sector. A number of industrial sectors, such as nuclear power, petrochemical, offshore, aerospace or pipeline girth weld applications have established FFS standards in place for the assessment of flaws found in-service. Some methods for design and remaining life assessments of fatigue-loaded structures are still unduly conservative in different loading regimes. Hence, there is still a need to generate a general purpose, unified, comprehensive and updated FFS methodology in Europe by covering four major failure modes (fracture, fatigue, creep and corrosion) in metallic load bearing components with or without welds. As a result, the European Community funded the project FITNET in the form of a Thematic Network (TN) organisation to review the existing FFS procedures and develop an updated, unified and verified European FITNET FFS Procedure to cover structural integrity analysis to avoid failures due to fracture, fatigue, creep and corrosion. FITNET TN is a four year project with the objective of developing and extending the use of FITNET FFS Procedure for welded and non-welded metallic structures throughout Europe. It is partly funded by the European Commission within the fifth framework programme and launched at February 2002. The network currently consists of 50 organisations from 16 European and three non-European countries representing various industrial sectors and academia. Further information can be found in the FITNET TN website: http://www.eurofitnet.org. FITNET Fitness-for-Service analysis of engineering structures aims to provide better design principles, support for fabrication of new components, prevention of service failures due to fracture, fatigue, creep and corrosion damages (no coverage of structural instability due to buckling). FITNET FFS criteria can be used to establish the size limits for defects in various engineering structures and can provide substantial cost savings in operating such structures. The use of the FITNET FFS Procedure involves making an assessment of a component containing a defect to ensure its structural integrity for its intended design life or until its next inspection period. The outcome of the assessment of a component in service is a decision to operate as is, repair, monitor (including re-setting of inspection intervals), or replace. The aim of this paper is to give an overview of the objectives and technical content of the FITNET FFS Procedure currently developed and validated by the European Fitness for Service Network FITNET and hence inform the offshore technical community.
Improvements to the Fracture Assessment of Welds Using FITNET Fitness for Service Assessment Procedure
Authors: Koc¸ak Mustafa , Seib Eduard , Motarjemi Afshin
Published: November 2008

Recent developments of the advanced welding processes such as laser beam welding (LBW), solid state friction stir welding (FSW) and hybrid welding, numbers of advanced structures are being designed and constructed in industries such as aerospace, power generation, oil and gas transmission and transportation. Development of new structural aluminum and magnesium alloys as well as high strength steels provide further possibilities for the welded structures in similar and dissimilar (material-mix) configurations. Consequently, there is an increasing demand for “Fitness-for-Service” (FFS) assessment of those advanced welded structures by considering the specific features of these weld joints (such as narrow weld width, high strength mis-match, etc.). In year 1999, Structural Integrity Assessment Procedure SINTAP has been developed for analysis of flaws to avoid fracture within the European Commission funded project SINTAP. Recently, the European Community funded project FITNET in the form of a Thematic Network (TN) organisation has started to review the existing FFS procedures and develop an updated, unified and verified European FITNET FFS Procedure to cover structural integrity analysis to avoid failures due to fracture, fatigue, creep and corrosion. This new FFS Procedure has adopted the SINTAP approach for assessing of the welded structures. This paper describes the FITNET FFS weld assessment route and also aims to demonstrate suitability of weld joint assessment route of the FITNET FFS Procedure in prediction of the critical conditions of various advanced welded joints containing flaw. The welded specimens used in this work cover conventional multi-pass welded Inconel-718 turbine blade (T-joint), center cracked wide plates of electron beam welded 13% Cr supermartensitic stainless steel, laser beam welded shipbuilding C-Mn steel and aluminum alloy. The results are showing that the weld strength mismatch analysis option of the FITNET FFS is conservative and degree of conservatism is similar to the analysis options for the homogeneous materials. This provides confidence in the use of the FITNET FFS procedure for assessing of the structural significance of flaws in welded structures.
A Non-Dimensional Weight-Velocity Parameter for Estimating Drag Force and Net Deformation of Gravity Fish Cages
Authors: Vikestad Kyrre , Lien Egil
Published: November 2008

Most floating fish cages consist of a floating cage collar, mooring system, and net cage hanging freely down from the floater. Any current moving through the net will deform the net. This deformation depends on the current velocity, the nets ability to attract forces, and the gravity forces from weights at the lower end of the net. The forces on the net will vary with the deformation. This paper shows that for this kind of cage, a reduced velocity Vred = U·(ρ/2G)1/2, where G is the equivalent weight per area of the net, will be sufficient to estimate the drag force and deformation of the net. The present work is analytical, combined with computer simulations. The reduced velocity parameter could be used to determine the needed bottom weights. The quick estimation of the drag force on the net could be used as an input to mooring design.
Non-Linear Time Dependent Corrosion Wastage of Deck Plates of Ballast and Cargo Tanks of Tankers
Authors: Garbatov Y. , Guedes Soares C. , Wang G.
Published: November 2008

The corrosion wastage of deck plates of ballast and cargo tanks is analyzed based on a non-linear corrosion model. This model is able to describe an initial period without corrosion due to the presence of a corrosion protection system, a transition period with a nonlinear increase of wastage up to a steady state of long-term corrosion wastage. This model is applied to corrosion wastage data of deck plates collected by the American Bureau of Shipping. The objective of this work is to fit this corrosion wastage model to the service measured data, determining the values of the model parameters that represent the best fit to the data so as to describe how corrosion wastage varies in time as a result of generalized corrosion.
Well Head Production Floater: Experimental and Numerical Investigation
Authors: Le Boulluec Marc , Maisondieu Christophe , du Plessix Guillaume , Cordeau Cyril
Published: November 2008

A model of an oil production floater is experimentally tested in regular and irregular waves for both fixed and free-moving structure. Measurements mainly concern the rigid body motions and the free surface elevation at 24 locations: 6 inside a moon-pool and 18 along the walls and above an immersed pontoon. Two natural periods of oscillation are experimentally identified inside the moon-pool and compared to linear diffraction and radiation computation and analytical formulas. Outside the moon-pool the wave run-up can be significant and strongly nonlinear, some modal periods are identified and compared to simplified formulation.
Surprises of Tribo-Fatigue
Authors: Sosnovskiy Leonid A.
Published: November 2008

The analysis of three surprises of tribo-fatigue is given in this report.
Wear and Friction Behaviour of CGRP and WGRP Composites Subjected to Dry Sliding
Authors: El-Tayeb N. S. M. , Yousif B. F.
Published: November 2008

An experimental investigation has been undertaken on chopped strand mat 450-R-glass fiber and woven 600-glass fabric reinforced polyester (CGRP and WGRP) composites to study their tribological performance. In the present work, the tribological characteristics of both CGRP and WGRP composites were measured in three principal sliding directions relative to the chopped glass mat (CSM) and woven glass fabric (WGF) orientations in the composites. The friction and wear results are presented as function of normal loads, test duration/sliding distances, and sliding velocities for P, AP, and N-orientation of both CGRP and WGRP. The results of friction and wear of CGRP and WGRP composite were strongly influenced by all the test parameters. For both CGRP and WGRP composites, the highest friction coefficient and wear rates were observed for N-orientation. Fiber fracture, crack, fragmentation, peeling off, and debris formation and micro crack initiation in the matrix are the characteristics features of the worn surfaces that observed by SEM.
Troppy Phenomenon
Authors: Sosnovskiy Leonid A. , Shcharbakou Siarhei S.
Published: November 2008

In this report the system of differential equations of troppy is obtained and analyzed. Troppy is the phenomenon of residual surface waveform damages formation as the result of nonstationary deformation process in the region of contact interaction of the solid/solid elements of an active system. From theoretical point of view troppy phenomenon represents, for example, the result of stability loss of a roller’s motion on a shaft. Motion stability loss is characterized by self-excitation of oscillations in the system and accompanied by elastoplastic deformation of bodies in the contact area.
Non-Linear Signal Analysis Applied to Surface Wear Condition Monitoring in Reciprocating Sliding Testing Machines
Authors: Le´pore F. P. , De Mello J. D. B. , Santos M. B.
Published: November 2008

Experiments conducted on elastic bodies under friction forces shown that the dynamical system is self-excited by the non-linear behavior of frictional forces. The main objective of this paper is to study the vibrations signals measured on a reciprocating wear testing machine using non-linear signal analysis formulation. A two input and one output MISO model is proposed to represent the non-linear system dynamics. The global output is the sum of two outputs produced by one linear path associated in parallel with a non-linear path. This last path has a non-linear model that represents the friction force and another linear transfer function connected in series. Since the linear path is identified by traditional signal analysis, the nonlinear function can be evaluated by the global input/output relationships, and can be correlated to wear conditions of the contact surfaces. Validation tests are conducted in a tribological system composed by a sphere in contact with a prismatic body witch has an imposed harmonic motion.
Wear and Failure Model for Lifetime Estimation of Solid Lubricated Rolling Contacts
Authors: Madan I. , Li X. , Bozkurt H. , Birkhofer H.
Published: November 2008

Solid lubricants are applied in rolling bearings when conventional oil and grease lubrications do not meet the advanced requirements of modern technology. One factor which limits the application of solid lubricated rolling bearings is the absence of lifetime estimation. In contrast to conventional liquid lubricated rolling bearings, for which the lifetime can be calculated with the Lundberg and Palmgren theory based on contact fatigue, there is no calculation available for solid lubricated rolling bearings. In this paper, a prediction method of lifetime based on wear and failure models is represented. A modified dynamic four ball tester, used in testing dry lubricated rolling contacts, is also introduced.
The Tribology of Carbon, Hydrogen, and Silicon-Containing Solid Lubricants (Keynote)
Authors: Harrison J. A. , Gao G. T. , Chateauneuf G. M. , Schall J. David , Van Workum Kevin , Mikulski P. T.
Published: November 2008

Constant temperature molecular dynamics simulations and the adaptive intermolecular reactive empirical bond-order potential energy function [1] (AIREBO) were used to examine the tribology of model self-assembled monolayers (SAMs) attached to diamond substrates. Two types of monolayers were examined. One was composed of alkane chains containing 14 carbons atoms and the other was composed of equal mixtures of 12 and 16 carbon-atom chains. The simulations have yielded unique insight into the origin of the friction differences between the two monolayer systems.
Application of Acoustic Emission for High-Pressure Short Time Solidification of Traction Fluids
Authors: Ohno Nobuyoshi , Tokunaga Wataru
Published: November 2008

The lubricating oils solidify at quasi-static high-pressure as the amorphous or glassy solids are verified by a number of studies. However, solidification of lubricating oil under the dynamic condition as the rolling bearings and the traction CVT is not clear. The high-pressure short time solidification of traction fluids is examined by the analysis of dent after the impact tests and AE analysis under impact loads. The intensity of each impact collision is measured by means of an acoustic emission (AE) sensor. The dimensionless AE r.m.s value is investigated by based on phase diagram of testing oils. It was recognized the solidification of oil under the dynamic high-pressure condition almost corresponded to the static condition.
Nano Particles’ Behavior in Chemical Mechanical Polishing With the Effect of Non-Newtonian Properties of Slurry
Authors: Chen Haosheng , Chen Darong , Wang Jiadao
Published: November 2008

Particle’s behavior in the slurry with power-law viscosity shows great effect on the wafer surface polishing process. Hydrodynamic pressure is periodically generated on the surface asperity when particles are passing through. Due to the periodical pressure, fatigue fracture occurs and begins from the top to the bottom of the asperity, then the material on the top is removed. Removal rate is calculated based on the energybalance fracture theory, and the result shows good agreement with experiment data. The effects of the particle size and the slurry film thickness are also discussed.
Static and Kinetic Friction of Smooth Glass Surfaces Rubbed With Silicone Oils
Authors: Rapoport L. , Shmukler V. , Moshkovich A. , Verdyan A.
Published: November 2008

The study of the effect of waiting time, loading and unloading on static and kinetic friction for real contact micro-systems was carried out. Three types of silicone fluid with the viscosity of 100, 450 and 5000 cSt at 25° C were used. Stop-start experiments allowed us to estimate the relaxation time after the static friction overshoot. For silicone liquid with viscosity of 100 cSt, relaxation of friction force (F) after the static friction overshoot occurred over one cycle of testing. Relaxation of F for fluids with the viscosity of 450 and 5000 cSt occurred during a long time and this effect was opposite for these silicone liquids. The analysis of loading-unloading cycles showed only a partial reversibility of F. The results were compared with static friction and stick-slip data obtained in other works, using SFA and FFM techniques. In order to explain the effect of viscosity and structure of the lubricant layers on stick-slip phenomenon, interior and wall slip of the lubricant film is discussed.
Meniscus Adhesion at Ultra-Low Flying Slider-Disk Interfaces
Authors: Mate C. Mathew , Payne Robert N. , Baumgart Peter , Kuboi Kathy
Published: November 2008

As head-disk spacings in disk drives approach a few nanometers, adhesive forces between the slider and disk can drastically alter the slider flying dynamics. At these small separations, it is still unclear, however, what type of adhesive force dominates. Most previous studies have concentrated on van der Waals and electrostatic attractive forces [1], which are readily incorporated into air bearing simulations. In this talk, we provide experimental evidence that the dominant adhesive force originates from menisci forming around the low flying portions of the slider air-bearing-surface as the spacing transitions from near-contact to contact.
Thermo-Elasto-Hydro-Dynamic Modeling of Hydrostatic Seals in Reactor Coolant Pumps
Authors: Galenne Erwan , Pierre-Danos Isabelle
Published: November 2008

The French energy company EDF has experienced in the last years some problems in managing reactor coolant pumps (RCP) seals in operation. That’s why a thermo-elasto-hydrodynamical model of the seal has been developed. The present model is a steady two-dimensional approach so as to characterize the normal operating mode of the seal. Numerical results are successfully compared to experimental results of leak-flow rate. The influence of pressure drop and injection temperature is described. The influence of the conicity of the faceplates is underlined. The friction is introduced in the model in order to reproduce the hysteretic behavior of the seal. The development of this model leads to a better knowledge of the behavior of a critical component.
A Comparison of Elastic Contact Modeling Utilizing Statistical and Fractal Approaches
Authors: Kogut Lior , Jackson Robert L.
Published: November 2008

Statistical and fractal approaches for characterizing surface topography have been used widely in contact mechanics. In the present study, an attempt is made to compare between contact mechanics results obtained with statistical and fractal approaches to characterize surface topography. Specifically, a three-dimensional fractal surface was generated and statistical surface parameters were extracted using different sampling resolutions. Contact mechanics simulations were performed using the simulated fractal surface and statistical surfaces represented by the extracted statistical surface parameters. Purely elastic contact is studied in order to eliminate the influence of the individual asperity mechanical response on the obtained results. Therefore, differences in the simulated contact area and load can be related solely to the different approach employed for surface characterization. The influence of surface characterization approaches on the contact parameters and the resulting predictions is discussed in the contents of the presented results.
Effects of Surface Texturing on Lubrication Theory: Consideration of Electrodouble Layer (EDL)
Authors: Li Wang-Long
Published: November 2008

The effects of surface texturing on the electrohydro-dynamic lubrication with thin double layers are considered for the sliding of one charged body past another in an electrolyte solution. The averaged Reynolds type equation as well as the related flow factors is then derived by the flow factor method. The couple effects of surface roughness and EDL appear on flow factors are discussed. The hydrodynamic pressure generated by the viscous force and electrokinetic force are discussed for an 1-D slider bearing.
Prediction Model of Surface Topography Evolution Due to Micropitting
Authors: Wang P. , Hua D. Y. , Keith T. G.
Published: November 2008

Micropitting is often observed on hardened materials that are involved with rolling/sliding contact. Even though micropitting is not a catastrophic failure, it may lead to excessive wear or macroscopic pitting. Field experiences and lab testing results have demonstrated that micropitting has a strong correlation to surface topography. Surface asperity contact induces elevated stresses that in turn cause near surface material distress. In this study a micropitting prediction model, based on the contact stresses of rough surfaces, is proposed. Surface topography is modified due to micropitting. The modification of the surface topography causes a redistribution of the contact stresses. Consequently, the intervention between surface topography and the stress field may form a course of surface degradation, or the contact surface may reach steady state without generating any further micropits. The evolution of surface topography is demonstrated for different surface finishes. The comparative micropitting wear volumes and depths are summarized for these finishes.
Rubbing Surface Reactivity of Alloy 718 Under Controlled Oxidation Conditions
Authors: Adamou A. S. , Denape J. , Paris J.-Y. , Andrieu E.
Published: November 2008

The high interdependence between the local thermo-mechanical stresses and physicochemical reactivity of the surfaces constitutes a recurring difficulty in formalizing dynamic models of interfacial processes [1,2]. The presence of oxide layer on the surface of metal and alloy is usually reported to reduce friction and wear by preventing direct metallic junctions. The atmosphere and temperature control the surface reactivity, and the protective ability of oxide layers depends on their morphology and chemistry, which determine their resistance [3]. The structuring and the organization of these phenomena into a hierarchy, require test procedures in which the thermal and environmental parameters are precisely controlled in order to define their impact on overall tribological behavior.
Properties of Ti-Si-N Nanocomposite Coatings Deposited by Closed-Field Unbalanced Magnetron Sputtering
Authors: Zhang C. H. , Lu X. C. , Luo J. B. , Shen Y. G. , Li K. Y.
Published: November 2008

Ti-Si-N coatings with different silicon contents were deposited by reactive magnetron sputtering. These coatings were characterized and analyzed by using a variety of analytical techniques. The Ti-Si-N coating shows a denser structure as compared with TiN coating, and consists of TiN crystallites and amorphous Si3N4 phase. The maximum hardness and Young’s Modulus of 52 GPa and 360 GPa respectively are achieved as the Si content was 8.6 at.%. The Ti-Si-N coating with 8.6 at.% Si shows the excellent oxidation resistance behavior and perfect anti-wear performance.
A New Model of Thermoelastohydrodynamic Lubrication in Dynamically Loaded Journal Bearings
Authors: Fatu Aurelian , Hajjam Mohamed , Bonneau Dominique
Published: November 2008

A comprehensive method of thermoelastohydrodynamic (TEHD) lubrication analysis for dynamically loaded journal bearings is presented. The Reynolds equation in the film is solved using the Finite Element (FEM) discretization. Thermal distortions as well as the elastic deformation of the bearing surfaces are computed using FEM method. The lubrication film temperature is treated as a time-dependent three-dimensional variable with a parabolic variation with respect to the film thickness. In order to compute the film and solid temperature, a new heat flux conservation algorithm is proposed. Fourier series approximate the instantaneous temperature fields in the solid boundary layers. Solving the complex problem of big end connecting rod bearing TEHD lubrication proves the algorithm efficiency.
The Transient Thermal Stress and Deflection of a Brake
Authors: Huang Yuan Mao , Chen Shih-Han
Published: November 2008

This study utilizes the finite element method with a two-dimensional model of a disk brake and investigates its distributions of the transient temperature, thermal gradient, heat flux, thermal stress and deflection due to friction. A specified initial uniform temperature of the disk is used to simulate heat transfer of the disk. Since the temperature of the disk brake inboard is higher than that of the disk brake outboard, the deflection of the disk brake inboard is larger than those at other locations. The maximum deflection of 0.4 mm occurs at the outer diameter of the disk inboard. The disk expands radial outward and bends from the disk brake inboard toward the disk brake outboard. The coning angle between the disk outboard surface and the original vertical disk outboard surface is 0.39°, which is comparable with the existing datum of 0.35°. The principal stresses at the lower mounting location are 184 MPa and 236 MPa. The calculated safety factor is 1.27 based on the modified Mohr theory used for brittle materials, and this disk brake is reliable.
PVD-Based Microstructuring Surface Techniques for Tribological Applications
Authors: Alberdi A. , Marin M. , Etxeberria I. , Alberdi G.
Published: November 2008

Combined techniques of Physical Vapour Deposition (PVD), laser ablation and UV-Photolithography have been set up to produce well defined surface textures able to increase the seizure resistance of high loaded lubricated systems. Using these new techniques, different predefined surface textures, following rectangular grid and zigzag stripped patterns have been generated. The microstructured surfaces developed have been characterised with confocal microscopy, optical and scanning electron microscopy. Ball-on-disc tribological tests under progressively increased load have been carried out using mineral oil as lubricant to determine the influence of surface microtextures on seizure resistance. The influence of shape and size of texture patterns on the tribological performance of the surface have been also studied.
Nonlinear Time Transient Stability Analysis of Multilobe Bearings
Authors: Kakoty S. K. , Kalita M. , Thivagar T.
Published: November 2008

In some specialized applications, plain circular bearing is mostly replaced by some other bearings, as plain bearing does not suit the stability requirements of high-speed machines and precision machine tools. Grooved circular bearings and multi-lobe bearings with two lobes, three lobes and four lobes are commonly used. The present work gives insight into nonlinear transient analysis of multi lobe journal bearing systems. An attempt has been made to evaluate the critical mass parameter (a measure of stability) for various values of aspect ratios besides finding out the steady state characteristics of multilobe journal bearings (two grooved, two lobe, three lobe and four lobe) such as load bearing capacity, Sommerfeld number and attitude angle At moderate and heavy load conditions (Sommerfeld number from 0.1 to 0.3), four-lobe bearing is most stable. Three-lobe bearing is the best in the range of Sommerfeld number from 0.3 to 0.8. Two-lobe bearing is found to be more stable than other bearings beyond this range.
The Effect of Different Lubrication Regimes and Lubricants on the Friction Hard-on-Hard Total Hip Replacements
Authors: Williams Sophie , Jin Zhongmin M. , Stone Martin H. , Ingham Eileen , Fisher John
Published: November 2008

The wear of hip replacements can be dependent on serum protein levels and the swing-phase load during the gait cycle. We hypothesise that these effects may be associated with changes in the lubrication and friction of the joint. The aim of this study was to assess the effect of the lubrication regime and lubricant on the friction of metal-on-metal (MOM) and ceramic-on-ceramic (COC) THRs. Increasing the swing-phase load led to decreased fluid film thickness and an increase in friction, in both MOM and COC bearings. Increasing the protein concentration of the lubricant, decreased the friction of MOM THRs. Friction testing of COC bearings demonstrated an increase in friction as the protein concentration increased. The change in lubricating film thickness explains differences in friction and wear as the swing-phase load is changed for a given lubricant. However, when we change the lubricant composition, protein boundary lubrication effects dominate, this influences friction and wear differently in MOM and COC THRs.
Lubrication and Dynamic Characteristics of a Cylinder Block in an Axial Piston Pump
Authors: Ahn S. Y. , Rhim Y. C. , Hong Y. S.
Published: November 2008

Lubrication characteristics between a cylinder block and a valve plate in axial piston pumps play an important role in volumetric efficiency and durability of a hydraulic unit. In this paper, the finite element method is used for the computation of the pressure distribution between a cylinder block and a valve plate of the axial piston pump. Also, the Runge-Kutta method is applied to simulate the dynamics of a cylinder block of three-degrees of freedom motion. From the results of computation, two major conclusions are drawn. One is related to the fluid film characteristics between a cylinder block and a valve plate, and the other is related to the average leakage flow rate which is determined by the pressure gradient and the clearance near the discharge port. To confirm results of numerical simulation of cylinder block dynamics, experiment is conducted using three eddy-current type gap sensors, which are imbedded at the pump housing. Finally, a revised shape of a valve plate is proposed which increases the stability of the cylinder block dynamics and the volumetric efficiency of the pump based on numerical simulation.
Tribology Character of Steel Archimedes Worm Gear
Authors: Xia Yanqiu , Wang Shijie , Hu Junhong , Zhou Feng , Xu Tao
Published: November 2008

The anti-wear and extreme pressure (EP) properties of several lubricant additives in base oil were investigated on four-ball friction and wear tester. The worn surface morphologies of the steel ball specimens were observed and analyzed with SEM and XPS. Ring-block friction and wear tester simulated Archimedes worm gear transmission. Steel/steel pairs were investigated in ring-block tester. Steel Archimedes worm gear replace copper Archimedes worm gear were investigated on opened-circuit test rigs with synthesizing Archimedes steel worm gear running-in lubricants and steel Archimedes steel worm gear lubricants.