bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Phenomena in Engineered Cartilage With Tissue Development in Agarose Gel
Authors: Kitajima Y. , Sugino S. , Sanada T. , Sawae Y. , Murakami T. , Watanabe M.
Published: March 2009

The primary function of articular cartilage is to absorb impact in life cycle, however once cartilage is damaged, it has poor ability to recover. And then transplant of engineered cartilage tissue is considered as the promising measure for the therapeutic approach, since it is free from immune reaction. Articular cartilage consists of 2% chondrocyte and 98% extra-cellar-matrix (ECM), which is made by chondrocyte’s metabolic action. ECM shows high osmotic pressure, mainly due to highly negative charged proteoglycan, and hence retain large amount of water. The most characteristic nature of cartilage tissue is avascularity, hence materials, such as nutrition and wastes, are transported from connective tissue or periosteum by mainly diffusion. One of the most significant key factors to control the development of the engineered cartilage is this transport phenomenon, which is, on the other hand, strongly affected by the tissue development. Therefore we study transport processes as ECM development. In this study, we selected ultra-low gelling temperature agarose gel, of different types and weight percent, as the scaffold, and chondrocytes were isolated from the bovine metacarpal-phalangeal joint. Engineered cartilage was obtained by incubating cell-agarose compounds for ECM to be produced. Engineered cartilage tissue specimens were soaked with fluorescent labeled dextran of prescribed molecular weight to observe the diffusion transport process. We evaluated diffusion coefficients by two different methods, namely, global observation in specimen by using flow chamber and local observation diffusion using FRAP method. We compare coefficients of dextran molecules both in engineered cartilage and cell-free agarose gel. First we investigate the effects of tissue development on diffusion coefficients. We observe the effects of incubation periods on the diffusion coefficients of engineered cartilage. And then we investigate the charge effects on the transport phenomena, by comparing the transport processes of charged and uncharged dextran. We also investigate the effects of scaffold type on tissue development.
Thermodynamic Effect on Rotating Cavitation in an Inducer
Authors: Yoshida Yoshiki , Sasao Yoshifumi , Watanabe Mitsuo , Hashimoto Tomoyuki , Iga Yuka , Ikohagi Toshiaki
Published: March 2009

Rotating cavitation in inducers is known as one type of cavitation instability, in which an uneven cavity pattern propagates in the same direction as the rotor with a propagating speed ratio of 1.0–1.2. This rotating cavitation causes shaft vibration due to the increase of the unsteady lateral load on the inducer. On the other hand, cavitation in cryogenic fluids has a thermodynamic effect because of the thermal imbalance around the cavity. It improves cavitation performances due to the delay of cavity growth. However, the relationship between the thermodynamic effect and cavitation instabilities is still unknown. To investigate the influence of the thermodynamic effect on rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74 K, 78 K and 83 K) with a focus on the cavity length. At higher cavitation numbers, super-synchronous rotating cavitation (Super-SRC) occurred at the critical cavity length of Lc/h ≅ 0.5 with a weak thermodynamic effect in terms of the fluctuation of cavity length. In contrast, synchronous rotating cavitation (SRC) occurred at the critical cavity length of Lc/h ≅ 0.9–1.0 at lower cavitation numbers. The critical cavitation number shifted to a lower level due to the suppression of cavity growth by the thermodynamic effect, which appeared significantly with rising liquid temperature. The unevenness of cavity length under synchronous rotating cavitation was decreased by the thermodynamic effect. Furthermore, we confirmed that the fluid force acting on the inducer notably increased under conditions of rotating cavitation, but that the amplitude of the shaft vibration depended on the degree of the unevenness of the cavity length through the thermodynamic effect.
Experimental and Numerical Analyses of Friction Factors in Offset Strip Fin Heat Exchangers
Authors: Wang Aihua , Moujaes Samir F. , Chen Yitung , Ponyavin Valery
Published: March 2009

Heat transfer in compact heat exchangers is augmented by the introduction of the offset strip fins. With the breakdown of the thermal and hydro boundary layers to boost heat transfer, the fins increase the friction power. Two heat exchangers of different fin geometries structures were built and tested. The results of the study show that the round-edge-fin heat exchanger has the smaller friction factor. A test rig was constructed to measure the friction factor of the offset strip fin heat exchangers with air. A modified hydraulic diameter was used to calculate the main parameters. The computational fluid dynamics package FLUENT was used to predict the flow in the heat exchanger. The numerical investigation was conducted and compared with experimental measurements.
Multi-Objective Design Exploration of a Centrifugal Impeller Accompanied With a Vaned Diffuser
Authors: Sugimura Kazuyuki , Obayashi Shigeru , Jeong Shinkyu
Published: March 2009

The problem of designing a centrifugal blower was explored using multi-objective genetic algorithm and data mining techniques. Blade-to-blade regions of an impeller and a diffuser were modeled and time-averaged non-uniform inflow to the diffuser was considered. The design objectives were blower efficiency and uniformity of the inflow to the diffuser. The impeller’s shape was represented by NURBS curves and then optimized. The obtained non-dominated solutions showed a trade-off relationship and the design variables controlling the trade-off were found to be related to the dimensions of the vane-less diffuser and the load balance of the impeller. We also applied Decision Tree Analysis and Rough Set Theory to reveal design rules, which led to good performance. Although the design rules derived from the optimization result and data mining results partly agreed with each other, we also clarified that there were some differences due to the characteristics of the data mining methods we used.
Direct Numerical Simulation of Reactive Mixing in a T-Shaped Micro-Reactor
Authors: Bothe Dieter , Lojewski Alexander , Warnecke Hans-Joachim
Published: March 2009

The large area-to-volume ratio of micro-reactors gives prospect of better yield and selectivity than for conventional designs, since diffusive fluxes of mass and heat in micro-devices scale with the area, while the rate of changes corresponding to sources and sinks are proportional to the volume. Indeed, theoretical considerations of the scaling behavior support the fact that micro-reactors allow for faster chemical reactions and provide better thermal control; cf., e.g., [1]. For applications in Chemical Reaction Engineering, the mixing of chemical species is of special interest, since it is an essential condition for chemical reactions to occur. Avoiding large pressure drops, laminar flow fields with secondary flows are chosen to increase the contact area between the inflowing educts. In this laminar but complex flow, the mixing state is determined by the interplay of convective and diffusive transport phenomena and, hence, a thorough CFD-simulation of yield and selectivity of such a reacting flow requires the resolution of the finest length scales of both the velocity and the concentration field. In order to reduce the numerical complexity we employ a simplified mathematical model of the relevant convection-diffusion-reaction equations similar to the parabolized Navier-Stokes system.
Single Water Drop Impingement Onto a Falling Water Film
Authors: Okawa Tomio , Shiraishi Takuya , Tada Takeshi , Kataoka Isao
Published: March 2009

The process of oblique impact of single water drops onto a water film falling down on an inclined wall was observed using a high-speed camera. The angle between the velocity vector of the impacting drop and the normal vector to the inclined wall was set to the values greater than 70°. In our previous experiments for the single water drop impact onto a quiescent water surface, no secondary drop was observed in this large impingement angle range. In the present experiments, however, secondary drops were produced occasionally during the collision process. The production of secondary drops was observed more frequently when the surface of falling liquid film was wavy. The process of the production of secondary drops from the falling water film was investigated using the video images to understand the difference between the drop impacts onto the quiescent film and onto the falling film. It was shown that the secondary drops could be produced when the primary drop collided against the bottom or the top of the wave. In the former case, it was considered that the impingement angle was overestimated in the present work since the effect of surface waviness was not taken into account. This would imply that the occurrence of splashing was predicted more precisely if the local inclination of film surface could be included in evaluating the impingement angle. In the latter case, it was inferred that the liquid flow formed below the film surface by the drop impact penetrated the film surface to produce secondary drops.
Steady and Unsteady Laminar Flow Past an Equilateral Triangular Cylinder for Two Different Orientations
Authors: Faruquee Zakir , Olatunji Temitope V.
Published: March 2009

Unconfined fluid flow past an equilateral triangle was numerically studied for laminar incompressible flow. Two configurations of the cylinder were studied. In the first configuration; a vertex was placed upstream and a side was placed in the downstream position normal to the flow, while in the second configuration; the orientation of the triangle was reversed, i.e. the side normal to the flow was placed upstream and a vertex was placed at the downstream. Both steady and unsteady simulations were performed at 30 ≤ Re ≤ 150. The results clearly show that the orientation of the triangle with the vertex at the downstream side stabilized the flow and delayed the onset of vortex shedding. Significant differences of drag coefficient, wake length, and velocity distributions were found between the two orientations of the equilateral triangle.
Characteristic Parameters of a Tuned Magnetic Fluid Damper Under Magnetic Fields
Authors: Ohno Ken-Ichi , Shimoda Manabu , Sawada Tatsuo
Published: March 2009

Damping parameters of a tuned magnetic fluid damper [TMFD] using a tuned mass damper [TMD] analogy model are obtained from approximation to frequency responses of experiments used some sort of magnetic fluids in a cylindrical container. An effective mass is changed by a magnetic field from downside, however a significant change of surface shape of magnetic fluids causes strange changing tendency. It was found that other parameters are changed according to the surface shape.
Design of Large-Scale, High-Efficient, Vertical Wind Turbine
Authors: Lee S. , Song W.-S. , Kim H.-R. , Park J.-G.
Published: March 2009

This paper presents the overall design of a 2 MW vertical-type wind turbine power generation system. Firstly, the performance of the jet-wheel turbo turbine was optimized by considering the design parameters such as the rotor inlet angle, the solidity, and the diameter-height ratio with the guide vanes fixed. The effects of the side guide vane and the opening area ratio upon the efficiency were tested. As the wind speed increases from 3m/s to 7m/s, the maximum power coefficient reached the limit value of about 0.6 based on the rotor area, which is much higher than those of ever-designed three-bladed horizontal turbines. The maximum power coefficients occurred at the tip speed ratio ranging between 0.6 and 0.7. Based on the performance of small prototype model, the large-scale wind turbine rotor was designed within the constraints of material cost, machining cost, structural safety at extreme conditions, and maintenance. Thus, the aspect ratio of the diameter-to-height and the hub-tip ratio were set as 0.8 and 0.0857, respectively. All sides of the rotor were almost opened to achieve a maximum efficiency with only possible blocking by the sprocket gear attached to the bottom of the rotor. To evaluate the structural safety of the turbine at extreme wind speeds over 25m/s lasting 10 minutes, the numerical simulations were performed to evaluate the pressure loadings on the blades and the guide vanes. According to the structural analysis based on the pressure loadings and its weight, the entire system is considered to be stable for the extreme and static loadings. The overall performance of the jet-wheel turbo wind-turbine system was analyzed to find the capacity factor for the wind characteristics of Gillim province in China by considering the gear box efficiency, the roller bearing losses, and the SCIG/DFIG generator efficiency.
Agitated Turbulent Flowfield of a Circular Jet With an Annular Synthetic Jet Actuator
Authors: Koso Toru , Kinoshita Takuya
Published: March 2009

An agitated circular turbulent jet with a coaxial annular synthetic jet actuator is investigated experimentally. The mean and turbulent velocities are measured by a hot-wire anemometer at a jet Reynolds number of 6400. The measured iso-velocity contour maps indicate that the width of the circular jet is increased even when the intensity of the alternating flow is too weak not to generate a synthetic jet. This can be attributed to the periodic disturbances by the actuator, which agitates the instability in the initial shear layer and moves the shear layer growth to upstream. With a strong agitation so as to generate a strong synthetic jet by itself, the agitated jet has the higher velocity and the larger width than those of unagitated jet. With this agitation, the momentum of the agitated jet is increased and its increment is equal to the momentum of the synthetic jet. Smoke visualization shows clearly that the actuator enhances the dispersion of primary jet fluids. These results are compared with those of a jet at a low Reynolds number of 3088 (Koso, 2005) and it is found that the mixing enhancement is qualitatively same for both Reynolds numbers, but the weak agitation is more effective in the low Reynolds number jet.
Visualization and Pattern Identification of the Cavitation-Bursting Phenomenon in Propeller Tip Vortices
Authors: Chow Yi-Chih , Lee Yaw-Huei , Kehr Young-Zehr
Published: March 2009

Marine propeller tip vortices are usually strong enough to induce cavitation in the vortex cores. Tube-shaped vapor cavity extending along the vortex trajectory becomes a way of visualizing the host tip vortex. Our preliminary observations show that, at certain flow conditions, the tip vortex cavity is going to burst into a fog-like micro-bubble cluster, along with a broad-band noise generation. This striking phenomenon and its application motivate us to study its origin and the associated multi-phase flow interactions. We plan to start by performing detailed visualization of the bursting cavitation and using the images obtained to identify the pattern of this cavity break-up process. The results are expected to elucidate the mechanisms involved, and to especially clarify the role of the non-cavitating vortex breakdown (bursting) scenario in forming such a cavitation-bursting phenomenon.
Fundamental Numerical Experiment for Validation of Ultrasonic-Measurement-Integrated Simulation Using Straight Tube Model
Authors: Liu L. , Hayase T.
Published: March 2009

In this study, as a fundamental study of the experimental validation of UMI simulation, we performed numerical experiment of UMI simulation with an axisymmetric straight tube model. We confirmed the validity of UMI simulation by reproducing the analytic solution, and it was found that the ultrasonic beam entry angle influences on the spatial and temporal convergence property of the UMI simulation.
Effects of Viscoelasticity on Drop Deformation in Shear Flows
Authors: Aggarwal Nishith , Sarkar Kausik
Published: March 2009

A three dimensional front tracking finite difference method is used to study the deformation of a Newtonian drop suspended in an Oldroyd-B fluid undergoing a steady shearing motion. The change in drop deformation and orientation with increasing Deborah number is established for small to moderate deformations and explained by examining the elastic and viscous stresses at the interface. Significant change in the drop orientation with the flow direction, with increasing viscoelasticity is observed. A non-monotonic change in steady state drop deformation is observed with increasing Deborah number and explained in terms of the competition between increase due to localized polymer stretching at the drop tips and decrease due to change in drop orientation angle.
The Impact of Surface Contamination on the Flow Beneath Wind-Generated Waves
Authors: Siddiqui Kamran , Loewen Mark R.
Published: March 2009

We report on an experimental study conducted to investigate flow characteristics in the near-surface layer beneath clean and surfactant-contaminated water surfaces in the presence of wind. The two-dimensional velocity field beneath the water surface was measured using particle image velocimetry. The water surface temperature measurements were made simultaneously using infrared imagery. The results show the existence of the viscous sublayer beneath both clean and contaminated water surfaces. Within the viscous sublayer in contaminated water, the mean streamwise velocity is 25–30% larger and the mean streamwise velocity gradients are more than a factor of two larger compared to that beneath clean water surfaces.
A Study for Introducing Engineering Design Process Into Engineering Design III in Kanazawa Institute of Technology
Authors: Sugimoto Yasuhiro , Sato Keiichi , Fujiki Nobuaki
Published: March 2009

In the engineering design III (ED III) course at Kanazawa Institute of Technology, the department of mechanical and mechanical systems engineering has tried to introduce the engineering design process in place of the conventional graduation study course. One of authors has presented several advantages of educational effects on the engineering design process. Now, it is necessary to improve the effects from the viewpoints of both students and teachers. This paper presents the results of questionnaires and interviews from both teachers and senior students at the department. Moreover we present the educational results under various kinds of viewpoints for introducing the method of the engineering design process into ED III.
A One Dimensional Mathematical Model for Urodynamics
Authors: Celik Ismail B. , Varol Asaf , Bayrak Coskun , Nanduri Jagannath R.
Published: March 2009

Millions of people in the world suffer from urinary incontinence and overactive bladder with the major causes for the symptoms being stress, urge, overflow and functional incontinence. For a more effective treatment of these ailments, a detailed understanding of the urinary flow dynamics is required. This challenging task is not easy to achieve due to the complexity of the problem and the lack of tools to study the underlying mechanisms of the urination process. Theoretical models can help find a better solution for the various disorders of the lower urinary tract, including urinary incontinence, through simulating the interaction between various components involved in the continence mechanism. Using a lumped parameter analysis, a one-dimensional, transient mathematical model was built to simulate a complete cycle of filling and voiding of the bladder. Both the voluntary and involuntary contraction of the bladder walls is modeled along with the transient response of both the internal and external sphincters which dynamically control the urination process. The model also includes the effects signals from the bladder outlet (urethral sphincter, pelvic floor muscles and fascia), the muscles involved in evacuation of the urinary bladder (detrusor muscle) as well as the abdominal wall musculature. The necessary geometrical parameters of the urodynamics model were obtained from the 3D visualization data based on the visible human project. Preliminary results show good agreement with the experimental results found in the literature. The current model could be used as a diagnostic tool for detecting incontinence and simulating possible scenarios for the circumstances leading to incontinence.
Two-Dimensional Numerical Simulation of Saltating Particles Using Granular Kinetic Theory
Authors: Marval Juan P. , Rojas-Solo´rzano Luis R. , Curtis Jennifer S.
Published: March 2009

Most granular flows at environmental conditions are unsteady and exhibit a complex physical behavior. Dune formation and migration in the desert are controlled not only by the flow of saltating particles over the sand bed, but also by turbulent atmospheric airflow. In fact, sediments are transported by the atmospheric airflow within a thin layer only a few centimeters above the sandy surface. These jumping particles reach a maximum sediment mass flux level at a certain delay time (known as the “saturation time”) after the initial movement by sliding and rolling begins. Unlike sediment transport in water where the particles are lifted by the turbulent suspension, the saltating particles are kept alive in the layer mainly due to particle-particle and particle-bed collisions. In order to model this Aeolian transport of sand, Jenkins and Pasini [1] proposed a two-fluid model (one-dimensional and steady state) using Granular Kinetic Theory (GKT) to describe the solid-phase stress. The present work extends the original idea of Jenkins and Pasini [1] by using a more robust model of GKT for the kinetic/collisional contributions to the solid-phase stress tensor, together with a friction model activated for sustained contacts between particles. In addition, a standard k-ε turbulence model for the air and a drag model for the interaction between the phases are employed. A rectangular 2D geometry was chosen with a logarithmic profile for the inlet air velocity, along with an initial amount of sand at rest in the lower part of the simulation domain, resembling the particle saltating flow commonly seen in the vertical middle plane within saltation wind tunnels. This model is validated with experimental data from Liu and Dong [2] and the results given by Pasini and Jenkins [1]. A good estimation for the particle erosion and mass flux in the saltation layer is predicted, even though the profiles of mass flux and concentration within the transport layer are very thin and lower.
Characterizing Pulsating Mixing of Slurries
Authors: Bamberger Judith Ann , Meyer Perry A.
Published: March 2009

This paper describes the physical properties for defining the operation of a pulse jet mixing system. Pulse jet mixing systems operate with no moving parts located in the vessel or in the fluid to be mixed. Pulse tubes submerged in the vessel provide a pulsating flow that mixes the fluid due to a controlled combination of applied pressure to expel the fluid from the pulse tube nozzle followed by suction to refill the pulse tube through the same nozzle. For mixing slurries nondimensional parameters to define mixing operation include slurry properties, geometric properties and operational parameters. Primary parameters include jet Reynolds number and Froude number; alternate parameters may include particle Galileo number, particle Reynolds number, settling velocity ratio, and hindered settling velocity ratio. Rating metrics for system performance include just suspended velocity, concentration distribution as a function of elevation, and blend time.
Nano and Micro Indentation and Scratch Tests of Mechanical Properties of Metals
Authors: Gitis Norm , Hermann Ilja , Kuiry Suresh , Khosla Vishal
Published: March 2009

Experimental comparison of common nano and micro scales for hardness evaluation has been performed on metal samples and discussed in details. Instrumented indentation was found advantageous in both repeatability and a number of measured parameters over classical hardness methods for metals, while sclerometry was advantageous for ultra-thin films.
The Effect of Coating on the Fretting Wear Between Tubes and Supports in a Nuclear Steam Generator
Authors: Lee Joong-Hui , Kim Jin-Sun , Park Jung-Min , Shin Bo-Ra , Lee Young-Ze
Published: March 2009

The steam generator in the nuclear power plants is a kind of heat exchanger, which is composed of bundles of long and slender pipes. The tubes are supported by anti-vibration bar to reduce the vibration, caused by the water flows for cooling purpose. The wear damage due to this vibration is called as the fretting wear, which should be minimized for the safe operation of plants. The hard coatings are very effective to reduce the amount of wear. In this paper, the coatings of TiN and CrN were deposited on the tube material to protect the fretting surfaces. The tube-on-flat type tester was used for fretting wear tests. The wear amounts of the coated tubes were decreased depending on coating thickness. CrN coating was very effective to reduce the wear. In case of TiN the wear amounts were dependent on the coating thickness. Thick coating of TiN was very effective for wear resistance.
A Model for Junction Growth of a Spherical Contact
Authors: Brizmer Victor , Etsion Izhak , Kligerman Yuri
Published: March 2009

The evolution of the contact area (junction growth) of an elastic-plastic preloaded spherical contact subjected to an additional tangential loading is investigated theoretically. The normal preloading leads to the formation of a junction that can support additional tangential load. A gradual increase of this tangential load, while the normal preload remains constant, can incept plasticity of the contact zone in case the initial normal preload was elastic or enhance an existing one, thus lowering the tangential stiffness of the junction. Finally, the tangential stiffness approaches zero which corresponds to sliding inception (i.e. loss of stability). The evolution of the contact area during the tangential loading prior to sliding inception reveals an essential junction growth which depends on the magnitude of the normal preload. The mechanism causing this junction growth seems to be new points of the sphere surface, which originally lay outside of the initial contact area that are coming into contact with the rigid flat during the tangential loading. A theoretical relation is developed for the dependence of junction growth on the normal preload, which correlates well with some limited experiments.
Pressure Calculation From Experimentally Evaluated Lubricant Thickness Within EHL Contacts
Authors: Vrbka M. , Vaverka M. , Poliscuk R. , Krupka I. , Hartl M.
Published: March 2009

This paper is concerned with elastohydrodynamic lubrication, especially determination of lubricant film thickness and contact pressure within a point contact of friction surfaces of machine parts. A new solution technique for numerical determination of contact pressure is introduced. Direct measurement of contact pressure is very difficult. Hence, input data of lubricant film thickness obtained from the experiment based on colorimetric interferometry are used for calculation of pressure using the inverse elasticity theory. The algorithm is enhanced by convolution in order to increase calculation speed. The approach gives credible results on smooth contact and it is currently extended to enable the study of contact of friction surfaces with dents.
Low Friction Composite Film Bearings
Authors: Szeri Andras Z.
Published: March 2009

Experts estimate that in 1978 alone over 4.22 × 1018 joule of energy were lost in the United States due to simple friction and wear — enough energy to supply New York City for the entire year. Energy loss through friction in tribo-elements is a major factor in limits on energy efficiency [1]. The two major approaches that have been pursued in the past for reducing frictional losses in tribological contacts were surface modification techniques such as laser texturing and modification of lubricant properties. Here we advocate yet another option, modification of the structural character of the lubricant film. The Composite-Film bearing (CFB) is investigating this third possibility.
Preliminary Evaluations of Composite CO2 Spray as a Machining Lubricant in Hard Turning and Conventional Milling
Authors: Jackson David P. , Greeley Mark H.
Published: March 2009

In the past century machining has witnessed an increasing demand for faster cutting, better finishes and longer tool life, all while machining more demanding materials. However, these demands are often at odds with one another; faster machining can greatly increase cut temperatures which leads to tool degradation and poor finish, and the need for finishing passes to improve dimensional tolerance and surface finish adds time to production.
Direct Simulation Monte Carlo Method for the Simulation of Rarefied Gas Flow in Discrete Track Recording Head/Disk Interfaces
Authors: Duwensee Maik , Suzuki Shoji , Lin Judy , Wachenschwanz David , Talke Frank E.
Published: March 2009

The direct simulation Monte Carlo method (DSMC) is used to study rarefied gas flow between an inclined plane slider bearing and a nano channel representing one groove in a discrete track recording head/disk interface. The forces acting on the slider are investigated as a function of slider pitch angle, disk velocity, track pitch, groove width, and groove depth. The influence of the absolute groove size on the slider forces is found to be small.
Optimization of Groove Geometry for Thrust Air Bearing to Maximize Bearing Stiffness
Authors: Hashimoto Hiromu , Ochiai Masayuki , Nanba Tadashi
Published: March 2009

Hydrodynamic gas film bearings are widely used for very high speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films for minimizing the vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is designed suitably, it is expected to improve considerably the stability characteristics of the bearings. However, the conventional bearing geometries are based on the fixed logarithmic spiral curve, and there is no literature treating how to change effectively the groove geometry to improve drastically the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be changed flexibly by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings, and the effectiveness of the methodology is verified experimentally.
A Reversed Solution for the Elastic Contacts Between Symmetrical Fourth Order Polynomial Surfaces
Authors: Diaconescu E. N.
Published: March 2009

The paper advances a combined, analytical-numerical solution for the elastic contacts between symmetrical, fourth order polynomial surfaces. This is based on a proposal for contact area and pressure distribution which must generate forth order polynomials for the deformed surface of the halfspace inside contact area. To check this proposal, the normal displacements inside contact area are computed numerically. These agree well with a fourth order polynomial. The effect of contact area and pressure coefficients upon the shape of pressure distribution is evidenced.
Effects of Electrokinetic Slip Flow on Lubrication Theory
Authors: Li Wang-Long
Published: March 2009

A lubrication theory that includes the effects of electric double layer (EDL) and boundary slip is developed. Both effects are important in microflow, and thus in lubrication problems. They have opposite effects on velocity distributions between lubricating surfaces. Also, the velocity distribution induced by the EDL stream potential (electroviscous effect) is affected by the boundary slip. Under the usual assumptions of lubrication and Debye-Hu¨ckel approximation for low surface potential, the Navier-Stokes equation with body force due to the electrical potential as well as the widely accepted Navier slip boundary conditions is utilized on deriving the modified Reynolds equation. Effects of EDL and boundary slip on the 1-D bearing performance are discussed by solving the modified Reynolds equation numerically.
Adhesion and Friction of a Biomimetic Mushroom-Shaped Fibrillar Microstructure
Authors: Varenberg M. , Gorb S.
Published: March 2009

Adhesion and friction of a novel biomimetic mushroom-shaped fibrillar microstructure were tested. The microstructure reveals approximately twice more effective adhesive properties than a control flat surface made of the same soft synthetic polymer. It also demonstrates smooth sliding with a friction coefficient approximately four times lower than that of the control surface which exhibits pronounced stick-slip motion. It appears that the new microstructure can be used in applications where a total attachment force needs to be generated in a binary on/off state and, most surprisingly, is suitable to stabilize and minimize elastomer friction.
Micro- and Nano-Tribological Behaviour of Soybean Oil-Based Polymers of Different Crosslinking Densities
Authors: Bhuyan S. , Sundararajan S. , Andjelkovic D. , Larock R.
Published: March 2009

Biopolymers produced from renewable and inexpensive natural resources, such as natural oils, have drawn considerable attention over the past decade, due to their low cost, ready availability, environmental compatibility, and their inherent biodegradability. In this study, the micro/nanotribological wear behavior of biopolymers of different crosslinking densities prepared from low saturated soy-bean oil (LSS) by Rh-catalyzed isomerization with divinyl benzene and polystyrene are evaluated and compared. Microtribological measurements were performed using a ball-on-flat reciprocating microtribometer using two different probes — 1.2 mm radius Si3N4 spherical probe and a 100 micron radius conical diamond probe with 90° cone angle. Nanoscale tests were done using a DLC coated antimony (n) doped silicon probe of radius ∼200 nm. Wear volumes were estimated from groove geometry using Atomic Force Microscope (AFM) and adhesive and abrasive wear coefficients were evaluated for the materials. Elastic modulus and hardness information were evaluated using tensile test and microhardness tests respectively. Correlations between cross-linking density and wear behavior were observed. These results provide some insight into the wear behavior of biorenewable materials.
Dynamic Coefficients of the Coupled Journal and Thrust Bearings Considering Five Degrees of Freedom for a General Rotor-Bearing System
Authors: Jang G. H. , Lee S. H. , Kim H. W.
Published: March 2009

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings considering tilting motion. The Reynolds equations and their perturbation equations are derived by linearization of bearing reaction with respect to the general five degrees of freedom, i.e. the tilting displacement and angular velocity as well as the translational displacement and velocity. Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between the journal and the thrust bearings. It also includes the Reynolds boundary condition in the numerical analysis to simulate the cavitation phenomena. The stiffness and the damping coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method can calculate the dynamic coefficients of a coupled journal and thrust bearing more accurately and efficiently than the differentiation method.
Nano Wear of Noble Metals Against Silicon
Authors: Peng Luohan , Liang Hong
Published: March 2009

We study the wear behavior of noble metals against a semiconductor substrate within a highly focused area. The nano-wear was generated on the tip of an atomic force microscope (AFM). The substrate is single crystal silicon. AFM tips were coated with noble metals, gold and silver, so that no complication of oxidation was introduced. The Au-Si and Ag-Si are two eutectic systems. The Au and Si atoms are more compatible compared with that of the Ag and Si system. During nano-wear experiments, the Au or Ag coated AFM tip slid against Si substrate. It was found that the Au tip showed adhesive wear but Ag tip showed abrasive wear. In this paper, we report results obtained in the nanoscale wear.
The Effects of Dimple Size and Depth on Friction Reduction Under Boundary Lubrication Pressure
Authors: Wang Xiaolei , Zhang Huan , Hsu Stephen
Published: March 2009

The effect of dimple size on sliding friction conducted under boundary lubrication conditions using a four-ball wear tester was investigated. The contact geometry used was a ball-on-three-flats arrangement using 52100 steel balls and flats. Circular dimples of various diameters (20–60 μm) and depth (2.5–10 μm) were fabricated using micro-lithography followed by electrochemical etching. Tests were conducted from 98–296N loads and 0.2–1.3 m/s speeds. Results suggest that smaller dimples with shallower depth achieve higher level of friction reduction under these test conditions.
Tribology and Cutting Performance of Esters as a MQL Machining Lubricant
Authors: Wakabayashi Toshiaki , Kishida Yasuo , Tsukuda Akira , Atsuta Toshifumi , Suda Satoshi
Published: March 2009

Synthetic esters have recently been used as a high performance lubricant in minimal quantity lubrication (MQL) machining. However, there is little understanding about the relationship between the cutting performance and the tribological action of these esters. This study therefore investigates the tribological characteristics of some synthetic polyol esters for MQL machining by using a basic friction test. In the results of this friction test, an ester having more ester bonds in one molecule showed the better lubricity and such trend was prominent at higher sliding speed in the range of the test conditions. The study also evaluated the practical cutting performance of these polyol esters by using a turning test. This evaluation presented, particularly at the cutting speed of 50m/min, an ester showing the better lubricity provided the higher cutting performance.
A New Rolling Contact Damage of Deep Groove Ball Bearing Under Grease Lubrication
Authors: Yoshioka Takeo , Shimizu Shigeo , Shimoda Hirokazu
Published: March 2009

A new type of rolling contact damage was found out in the fatigue tests of the deep groove ball bearings #6206 under pure radial load and grease lubrication. In appearance, the damages had a few cracks at perpendicular to the ball revolution direction, sank about 20 μ m in the surface of rolling raceway, happened only in the raceway of stationary races and surface of balls, and distributed widely within loaded zone. And in the cross section there were a lot of cracks propagated at 60∼80 degrees to the rolling surface at not only damage position but also other parts. The cracks at the damage position just opened to the surface. It is supposed that the damages are caused by rolling contact fatigue and metal to metal contacts due to lubricant starvation under grease lubrication.
Characterization of Titanium and Niobium Doped DLC Films Grown by Pulsed DC PVD: Closed Field Unbalanced Magnetron Sputtering (CFUBMS) Method
Authors: Ugur Deniz , Efeoglu Ihsan , Altintas Sabri
Published: March 2009

In this research, structural, tribological and mechanical characterization of Nb and Ti doped diamond like carbon (DLC) films was carried out. Films were grown on M2 high speed steel (HSS), glass and silicon wafer substrates by pulsed DC physical vapor deposition – closed field unbalanced magnetron sputtering (PVD-CFUBMS) method. Structural characterization of the coatings was done by using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) tests. Tribological characterization was completed by conducting pin on disk tests, scratch tests and surface profilometry analyses on wear scars. Hardness measurements were done with nanoindentation tests. It was noted that there existed excellent adhesion between the coating and the substrate, which is evidenced by the high critical loads reached in scratch tests.
EHD Lubrication of Multi-Body Common-Pin Conrod Big End Bearings System
Authors: Fatu Aurelian , Bonneau Dominique
Published: March 2009

This paper describes a model for the analysis of elastohydrodynamic (EHD) lubrication of a multi-body common-pin connecting-rod (conrod) big end bearing system. Two conrod and three thrust bearings are fully coupled in order to simulate real behavior of the system. An extended Reynolds equation including mass conservation and oil film history is solved in the big end conrod bearings. The HD behavior of the thrust bearings is simulated by a cylindrical coordinate Reynolds equation. By comparisons with classical single rod analysis results show the pertinancy of simulating twin moving conrods.
Traction of Lubricated Rolling Contacts Between Thin Film Coatings and Steel
Authors: Evans Ryan D. , Cogdell J. David , Doll Gary L.
Published: March 2009

Tribological thin film coatings can enhance performance in mechanical components such as bearings and gears. Although lubricant is present in most applications, the interactions of the lubricant with coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness Λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings are evaluated. A ball-on-flat test configuration is used in a 100% slide-to-roll condition. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance are observed for different coating types. The traction coefficient decreases at high Λ with increasing hydrocarbon content in the coating. The combination of coating micro-texture and composition are believed to influence traction as A becomes small.
Possible Effects of Low Sulfur Diesel Fuel in Locomotives
Authors: Girshick Fred W.
Published: March 2009

Diesel fuel with a maximum of 500 parts per million sulfur became mandatory for United States railroads in June 2007, with another reduction to 15 parts per million expected by 2012. These levels are significantly lower than the pre-2007 level of 5000 parts per million maximum. The use of these fuels will have several effects on locomotive engine operation, some good, some bad, and some merely different. This paper examines the possible effects of lower sulfur diesel fuel on locomotive engine operation, shares experiences from other parts of the world when lower sulfur fuel was introduced, and speculates on possible subsequent changes, including lubricant composition and the use of fuel-borne additives.
The Effect of UV Stabilizer on the Photo Degradation of Perfluoropolyether Lubricants Used in Hard Disk
Authors: Lee Jihye , Chun Sang-Wook , Kang Ho-Jong , Talke Frank E.
Published: March 2009

Ultraviolet (UV) light exposure can lead to photo degradation of perfluoropolyether (PFPE) lubricants, resulting in a change of their physical properties. In this paper, 2,3,4,5,6-pentafluorobenzophenone was used as ultraviolet stabilizer (UVS) to slow down the photo degradation of PFPE. PFPE/UVS mixtures were exposed to UV light and the mechanism of photo degradation was studied with nuclear magnetic resonance (NMR). Small amounts of UVS (less than 0.3 wt%) were found to effectively stabilize both UV photo degradation at the main chain and the end chain of PFPE.
Bismuth Lubrication of Rail-Armature Interface
Authors: Hsieh Peter , Ghosh Gautam , Fine Morris E. , Chung Yip-Wah , Wang Jane , Crawford Mark
Published: March 2009

Extreme operating conditions, as encountered in the sliding armature-rail interface in electromagnetic launchers, require novel lubrication schemes. Low melting-point metals may be effective in concurrently lowering the armature-rail electrical resistance and friction. Bismuth-coated armatures reduce rail wear while improving the efficiency over multiple launches. These metals may serve as liquid lubricants for other high-power sliding electrical contact applications.
Granular Flow Modeling and Simulation Using a Dynamic Finite Element Method
Authors: Kabir M. A. , Higgs C. Fred , Lovell Michael R.
Published: March 2009

Granular flow behavior is of fundamental interest to the engineering and scientific community because of the prevalence of these flows in the pharmaceutical, agricultural, food service, and powder manufacturing industries. Granular materials exhibit very complex behavior, oftentimes acting as solids and at other times as fluids. This dual nature leads to very complex and rich behavior, which is not yet well understood. Therefore, the present investigation introduces a new technique that can potentially be used to unveil the mystery of granular flow phenomena. To this end, advanced finite element modeling and simulation techniques have been applied to the study of the complex nature of granular flow. More specifically, the explicit dynamic code LS-DYNA has been utilized to gain an understanding of the complex flow nature and collision stresses of granules in a shear cell.
Wear of Electric Contact Surfaces
Authors: Song J.
Published: March 2009

Fretting corrosion is one of the important factors which limits the lifetime of electric contacts. In order to avoid fretting corrosion coatings of different precious metals are used. The wear resistance of the coating determines the lifetime of electrical contacts. The long term characteristics of gold coated electrical contacts with different additives and contact shapes are investigated and the results are analyzed. It is found out that the wear resistance of contact coating can be largely influenced by the amount of the additive in gold and by the design of the contact shape. Only the combination of an optimized contact shape with suitable coating materials leads to a long term stability of electric contacts.
Revisit to Stiffness of Bump Foils in Air Foil Bearings
Authors: Kim Daejong , Ezeka Chinedu , Kumar Manish
Published: March 2009

Air foil bearings have compliant elastic foundation to provide compliance to bearing surface and damping. The most widely used elastic structure is the corrugated bump foil. All the currently available formulas for the bump stiffness [1–3] do not consider bending moments at the bump supports and within the straight contact patch which connects the bumps. However, for continuous bump foils, bending moments at the support points where contact is made with the bearing sleeve cannot be neglected. This paper introduces a set of new formulations for stiffness of bump foils considering the bending moments at the support points. All the formulas were derived using computer algebra software. The results are compared with the result from other formula [3].
Effect of Bearing Profile on the Stability of Statically Indeterminate Rotor Bearing Systems
Authors: Feng N. S. , Hahn E. J.
Published: March 2009

The stability of rotating machinery consisting of flexible rotors supported by fluid film bearings is significantly affected by the dynamic characteristics of the bearings and in particular, the bearing profiles as well as the bearing reaction loads, which, in statically indeterminate systems, are in turn strongly influenced by the relative transverse alignment of the bearings. Using a simple four bearing statically indeterminate model, it is shown that relatively simple variants of the circular bearings, viz. elliptic and 2-pad offset bearings display better system stability characteristics systems in aligned situations and are also more likely to be stable in misaligned situations.