bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Surface Liquid Film on Cylinder Icing Under Marine Conditions
Authors: Lozowski E. P. , Kobos A. M. , Kachurin L. G.
Published: February 2008

A new steady-state icing model is presented Which explicitly takes into account the dynamics and thermodynamics of a liquid film on the ice accretion surface under high liquid fluxes. The film is generated by excess unfrozen impinging liquid, is set in motion by the aerodynamic shear stress, and is eventually shed. In order to keep the model simple, it is formulated for a rotating cylinder subjected to a continuous supercooled freshwater spray. The model is used to explore the physics of the liquid film, and confirms that the film is thin and laminar except possibly under extreme liquid fluxes. It predicts supercooling of several degrees at the film surface, in agreement with recent observations. Further, the model is used to investigate the dependence of the icing rate on the following parameters: liquid water content, air temperature, wind speed, spray temperature, cylinder diameter, and heat transfer coefficient.
Risk Assessment of Production and Storage Tankers
Authors: Vinnem J. E. , Haugen S. , Børresen R.
Published: February 2008

Production and storage tankers are being evaluated extensively for development of marginal oil and gas fields in the North Sea. The main safety aspects of these vessels are discussed, based on a number of quantitative risk assessments for these vessel concepts. These studies have confirmed the importance of several important safety features, such as a fire-protected, enclosed escape way along one of the sides of the ship. Other important safety features include weather-vaning capability as a function of the turret location, location and configuration of the flare system, protection of cargo tanks by inert gas blanketing, as well as procedures for strict control of tank intervention. The results, show that the production and storage vessels have favorable safety characteristics, and that these concepts represent an acceptable and feasible solution for the marginal fields.
Hydrodynamic Loads on a Conical Slender Cylinder
Authors: Galper A. R. , Miloh T.
Published: February 2008

We consider the problem of calculating the wave load distribution acting on a large conical vertical ocean structure (monotower) due to an ambient nonuniform flow field. Under the assumption of weak flow nonuniformity, it is demonstrated that the leading-order solution for a vertical structure with variable cross section exhibits nonlocal terms, in contrast with a straight column with a constant cross section.
Oscillating Turbulent Flow With or Without a Current About a Circular Cylinder
Authors: Sarpkaya T. , de Angelis M. , Hanson C.
Published: February 2008

CFD analyses of two benchmark, two-dimensional, sinusoidally oscillating, turbulent flows (one with zero mean and one with nonzero mean) at relatively large Reynolds and Keulegan-Carpenter numbers and relative current velocities, have been performed with CFD-ACE, a Favre-averaged Navier-Stokes (FANS) code. The primary purpose of the investigation was a critical assessment of the computational accuracy of time-dependent turbulent flows with large-scale unsteadiness. A number of turbulence models, including the standard k-ε, re-normalization group (RNG) based k-ε, and low-Reynolds number model have been employed. Among others, a second order in time, second order in space, second-level predictor-corrector finite-difference scheme has been used. The analysis produced the time-dependent in-line and transverse forces, the force coefficients, instantaneous velocity, vorticity, and pressure distributions, and streamlines. Representative results are compared with each other and with those obtained experimentally.
Mooring System Design Based on Analytical Expressions of Catastrophes of Slow-Motion Dynamics
Authors: Bernitsas M. M. , Garza-Rios L. O.
Published: February 2008

Analytical expressions of the necessary and sufficient conditions for stability of mooring systems representing bifurcation boundaries, and expressions defining the morphogeneses occurring across boundaries are presented. These expressions provide means for evaluating the stability of a mooring system around an equilibrium position and constructing catastrophe sets in any parametric design space. These expressions allow the designer to select appropriate values for the mooring parameters without resorting to trial and error. A number of realistic applications are provided for barge and tanker mooring systems which exhibit qualitatively different nonlinear dynamics. The mathematical model consists of the nonlinear, third-order maneuvering equations of the horizontal plane slow-motion dynamics of a vessel moored to one or more terminals. Mooring lines are modeled by synthetic nylon ropes, chains, or steel cables. External excitation consists of time-independent current, wind, and mean wave drift forces. The analytical expressions presented in this paper apply to nylon ropes and current excitation. Expressions for other combinations of lines and excitation can be derived.
Semi-Analytical Hydrodynamics and Motions for a TLP Structure—Part I:
Enhancement of Pontoon Results Using Two of Haskind’s Theorems
Authors: Mullarkey T. P. , McNamara J. F.
Published: February 2008

A semi-analytical solution procedure for the derivation of first-order wave forces, added mass, and damping terms is presented for rectangular pontoons which may be floating, submerged, or resting on the seabed. The development is based on a solution matching technique for the scattered and radiated wave potentials and gradients across common boundaries of the subdivided solution domain. The final expressions are true for waves of arbitrary angle of incidence and singularities due to the case of normal incidence are eliminated. The approach is also generalized for the case where the pontoon is a unit of a TLP offshore production system by referring all quantities to a global coordinate system. Numerical results are extracted for a number of benchmark problems and compared with independent values where available in the literature. Excellent agreement is obtained for wave forces, added mass, and damping Values for cases involving floating, submerged, and bottom-founded pontoon configurations.
An Alternative Stochastic Representation of Drag Forces on Offshore
Structures for Dynamic Analyses
Authors: Naess A. , Høegh Krohn L. J. , Pisano A. A.
Published: February 2008

A new method for stochastic representation of the hydrodynamic drag forces on offshore structures subjected to irregular waves is described. For the case of zero current, it is shown that it is possible to construct a genuinly quadratic representation of the drag force that reproduces the statistical properties of the standard formulation of the drag force closely, and which has a spectral density that approximates the desired force spectrum reasonably well. The distinct advantage of this representation is that it brings dynamic analysis back into the frequency domain, in a similar manner as achieved for a linearized force representation.
A Photoelastic Determination of Stress Intensity Factors for Corner Cracks in a Bolted Joint
Authors: Gu¨ngo¨r S. , Patterson E. A.
Published: February 2008

Three-dimensional photoelasticity was used to measure mode I stress intensity factors of corner cracks in a double-shear bolted joint. A model of the joint assembly was manufactured from a photoelastic material and three different corner cracks were introduced using a cutting wheel. After the stress freezing process, slices along the crack fronts were cut and analyzed using three different photoelastic procedures. There was good correlation between the methods of analysis. Stress intensity factors of these cracks were found to vary along the crack front with a maximum at the bore of the hole and a minimum on the surface of the plate. This implies that the cracks are likely to grow more rapidly along the bore.
Design Seastates for Extreme Response of Jackup Structures
Authors: Winterstein S. R. , Torhaug R. , Kumar S.
Published: February 2008

The extreme response of a jackup structure is studied. We consider how design seastate histories can be introduced to reduce the cost of time-domain response analysis. We first identify critical wave characteristics for extreme response prediction. In quasi-static cases, the maximum wave crest height, ηmax, is shown to best explain extreme deck sway. For more flexible structures we introduce a new wave characteristic, SD, based on response spectral concepts from earthquake engineering. Finally, we show how accurate response estimates can require fewer time-domain analyses, provided design seastates are pre-selected to ensure that ηmax or SD is near its average value. With respect to standard Monte-Carlo simulation, these design seastates achieve at least a 50-percent reduction in response variability, and hence at least a fourfold savings in needed simulation cost. These results may lend insight, not only into time-domain simulation, but also into more fundamental questions of jackup behavior. They also suggest that, at least in quasi-static cases, still simpler design wave methods based on ηmax may suffice. We illustrate and evaluate some such design wave methods here (e.g., the “new wave” model and others based on Slepian theory).
Analytical Models for Mooring Chain-Soil Interaction
Authors: Larsen K. , Svano̸ G.
Published: February 2008

For most catenary mooring systems, a quite long part of the line is resting on the bottom, even in extreme situations. Hence, a good design of the anchor requires an accurate prediction of the loading from the anchorline, including any soil-chain interaction. This requires that the longitudinal chain-soil characteristics are well described for different soil conditions and that efficient computational models exist. This is particularly important in fatigue design of e.g., suction anchors. Design against fatigue is in many cases critical for these type of anchors. A problem is the lack of design tools handling the soil-chain interaction correctly. Traditionally, the soil effects are neglected completely in a fatigue design process. A consequence in many cases is an expensive overdesign. There exist chain-soil models to be applied together with FEM programs. These are too impractical to use in efficient fatigue design which requires the load assessment due to many seastates. They also suffer from the lack of reliable soil parameters. The paper addresses analytical models of the tension and longitudinal displacement along the part of the line resting on the bottom, assuming the tension at “touch-down” to be known. Hence, only longitudinal chain-soil interaction is considered. The models are based on recently established soil parameters for longitudinal chain-soil interaction. Comparison with FEM computations shows that the analytical models are performing very well in the prediction of cyclic loads. They are therefore a major improvement to the existing design procedures for anchor design.
Preliminary Design of Differentiated Compliance Anchoring Systems
Authors: Garza-Rios L. O. , Bernitsas M. M. , Nishimoto K. , Masetti I. Q.
Published: February 2008

The preliminary design of a differentiated compliance anchoring system (DICAS) is assessed based on stability of its slow-motion nonlinear dynamics using bifurcation theory. The system is to be installed in the Campos Basin, Brazil, for a fixed water depth under predominant current directions. Catastrophe sets are constructed in a two-dimensional parametric design space, separating regions of qualitatively different dynamics. Stability analyses define the morphogeneses occurring across bifurcation boundaries to find stable and limit cycle dynamical behavior. These tools allow the designer to select appropriate values for the mooring parameters without resorting to trial and error, or extensive nonlinear time simulations. The vessel equilibrium and orientation, which are functions of the environmental excitation and their motion stability, define the location of the top of the production riser. This enables the designer to verify that the allowable limits of riser offset are satisfied. The mathematical model consists of the nonlinear, horizontal plane fifth-order large-drift, low-speed maneuvering equations. Mooring lines are modeled by open-water catenary chains with touchdown effects and include nonlinear drag. External excitation consists of time-independent current, wind, and mean wave drift.
Extreme Response of Nonlinear Structures With Low Damping Subjected to Stochastic Loading
Authors: Naess A.
Published: February 2008

The response of structures with low damping to random loading is generally characterized by significant clumping of the large response peaks. This clumping is known to affect the extreme responses of the structure. In the paper, we shall propose an approximate method to account for this effect on first passage times and extreme values of narrow-band random vibrations, both Gaussian and non-Gaussian. The method is based on the concept of joint crossing rates of a stochastic process. This makes it possible to introduce a correlation structure to the sequence of peak values, allowing the introduction of an approximate estimate of the effect of clumping on large excursions of the underlying narrow-band process. The advantage of the proposed method is that explicit, closed-form expressions for the clumping effect on first passage times and extreme values are obtained. The method is illustrated by application to specific examples.
A CFD Investigation Into the Effects of Current Incidence on the Hydrodynamic Loading on a Deepwater TLP
Authors: Teigen P. , Przulj V. P. , Younis B. A.
Published: February 2008

The use in the offshore engineering industry of computational fluid dynamics (CFD) to estimate the hydrodynamic forces due to steady, turbulent currents on offshore structures has so far been rather limited. This is largely due to the uncertainties inherent in obtaining accurate solutions to the governing Navier-Stokes equations, particularly for complex geometries and at high Reynolds numbers. In this study, we assess the contributions to such uncertainties arising from a number of factors. Those include the number of nodes in the computational mesh used to overlay the flow domain, the choice of scheme used to discretize the governing equations, the choice of turbulence model used to close the time-averaged equations, and the assumptions made regarding the state of turbulence in the incident current. The influence of these factors is systematically assessed with respect to the flow around a full-scale mini-TLP. The paper also assesses the influence of the current incidence on the hydrodynamic loads on the same TLP. A previous study by the same authors has suggested the presence of substantial “shielding,” whereby the computed steady-state loading on the TLP was found to be significantly lower than the value recommended by the DNV design code. Computations performed here with the direction of the incident current varied in the range 0–45 deg suggest that the extent of this shielding is significantly diminished at high angles of incidence.
Numerical Analysis of Nonlinear Wave Propagation in Elastic Submerged Cables
Authors: Behbahani-Nejad M. , Perkins N. C.
Published: February 2008

This paper analyzes the coupled nonlinear tangential-normal waves that propagate along underwater cable suspensions. Taken with the recently developed linear theory governing the in-plane structural waves (Behbahani-Nejad and Perkins, 1996) and an analysis of nonlinear out-of-plane waves for submerged cables (Behbahani-Nejad and Perkins, 1997), this investigation contributes further understanding toward a nonlinear three-dimensional theory for wave propagation along fluid-loaded cables. The nonlinearities present in the in-plane model render the cable/fluid model intractable by exact analytical methods. A numerical solution is pursued in this study using finite difference algorithms. To this end, an infinite cable domain is divided to two subdomains, namely an interior (finite computational) domain and exterior (infinite far-field) domain. Closed-form solutions for the approximate linear theory are employed for the far field in constructing nonreflecting boundary conditions for the computational domain. Numerical results highlight the governing role of nonlinear hydrodynamic drag for underwater cable suspensions. The numerical results further demonstrate that most analyses of cables in air are not useful for underwater cable applications.
Five-Axis Part Machining With Three-Axis CNC Machine and Indexing Table
Authors: Suh Suk-Hwan , Lee Jung-Jae
Published: February 2008

In this paper, we develop a versatile CAM method by which five axis machining can be effectively carried out with a three-axis CNC machine together with a rotary-tilt type indexing table. In this method, the part surface is divided into a set of subareas, and each subarea is machined by the virtually oriented tool whose orientation is provided via the index table. The key goal in developing our solution algorithm has been to minimizing the number of part setups (i.e., angle changes in the indexing table) and the surface ridges where multiple tool paths join. A robust algebraic solution procedure for achieving these practical criteria is presented, including the details of surface decomposition, tool path computation, and the interface of the index table. Since the developed method enables utilization of existing machines (equipped with three-axis control) for five-axis machining, the results are practically meaningful, especially for small to medium industries.
Constrained Cutting Rate-Tool Life Characteristic Curve, Part 2: Convex Programs
Authors: Hough C. L. , Chang Y.
Published: February 2008

Based on the concept in Part 1, Theory and General Case, algorithms to determine the constrained R-T characteristic curve are established for convex constrained machining economics problems. The first algorithm is for posynomial problems with the linear-logarithmic tool life equation. The R-T curve may be determined by applying the simplex method to the log-dual problems. Sensitivity analysis of the optimal simplex tableau enables obtaining the loci of optima easily. The second algorithm is for the quadratic posylognomial problems with quadratic-logarithmic tool life equation using the property of primal-dual feasibility. End milling examples constructed in Part 1 illustrate the algorithm comparing to the exhaustive method.
Suppression of Chatter Vibration in Drilling
Authors: Ema S. , Marui E.
Published: February 2008

In this study, from the viewpoint of suppressing chatter vibration in drilling, the effects of cutting conditions on the initiation boundary of chatter vibration were investigated experimentally. Furthermore, the application of an impact damper on drills was attempted to suppress chatter vibrations.
Development of a Die Shoulder Force Transducer for Sheet Metal Forming Research
Authors: Kernosky S. K. , Weinmann K. J. , Michler J. R. , Kashani A. R.
Published: February 2008

A force transducer has been developed for measuring the tension in a strip of sheet metal as it passes over a die shoulder. This transducer is primarily a research tool. The die shoulder portion of the transducer can be selectively fixed or permitted to roll by contact with the moving strip. Applications of this force transducer are to measure pull force, drawbead restraining force, calculate the average coefficient of friction over the die shoulder, and quantify bending effects. Described in this paper is the development of the force transducer. It is a design based on four webs with strain gages as the transduction elements. It has been built, calibrated, and shown to accurately measure sheet tension in a strip test apparatus before and after the portion simulating the die shoulder. Friction and bending effects are studied from the sheet tensions.
Technology Cost Modeling for the Manufacture of Printed Circuit Boards in New Electronic Products
Authors: Shina S. G. , Saigal A.
Published: February 2008

The rapid pace of technological and material advances has made it difficult to ascertain the most cost effective plan for manufacturing new products. The decision to identify the appropriate manufacturing methods and materials selection is most timely made during the initial design stage of the product. However, tradeoffs in manufacturing and materials technology are not easily discernible to the design team, while traditional cost accounting systems do not reflect the continuous improvements nor the opportunities in increasing quality and reducing cost. Systems that have recently been developed to assist in estimating new product cost, such as Activity Based Costing (ABC) and Technical Cost Modeling, focus on a stable manufacturing environment. They presume that production is either dedicated to the new product, or that utilization and/or yields of machines are at static levels. In most modern companies, the majority of new products introduced are evolutionary in nature, attempting to gain maximum advantage of current material and manufacturing technologies while continuing to be made alongside existing production. These new products can significantly change the current manufactured product and material mix, and hence their cost. A technology based modeling approach is presented in this paper to address the issues of changes in a dynamic manufacturing environment, where each design selection can be evaluated individually based on its production impact. Elements of this approach are described in the design of electronic products using printed circuit boards. The design team can select from a large combinations of technologies, materials and manufacturing steps, each with its particular cost, production rate and yield. A technology based cost modeling system can be developed to guide the team in the selection process by identifying the cost tradeoffs involved in each alternative design.
Error Source Diagnostics Using a Turning Process Simulator
Authors: Chen Sung-Gwang , Ulsoy A. Galip , Koren Yoram
Published: February 2008

To improve productivity and quality in machining, it is necessary to understand the interactions among machine tool components and the cutting process. This paper presents a model that characterizes interactions among the subsystems of a computer numerically controlled (CNC) lathe. The model is combined with a cutting force model to obtain a comprehensive turning simulator that simulates the cutting forces and part dimensions. A series of calibration experiments are proposed and implemented for process simulation. The simulation results are good when compared with experimental measurements. The interactions among the subunits of a CNC lathe and the cutting process are found to be potentially important.
Integration of Process Simulation in Machining Parameter Optimization
Authors: Stori J. A. , Wright P. K. , King C.
Published: February 2008

In recent years, simulation tools have proven valuable for the prediction of machining state variables over a wide range of operating parameters. Such simulation packages, however, are seldom an integral part of machining parameter optimization modules. This paper proposes a methodology for incorporating simulation feedback to fine-tune analytic models during the optimization process. Through a limited number of calls to the computationally expensive simulation tools, process parameters may be generated that satisfy the design constraints within the accuracy of the simulation predictions, while providing an efficient balance among parameters arising from the functional form of the optimization model. The following iterative algorithm is presented: (i) a non-linear programming (NLP) optimization technique is used to select process parameters based on closed-form analytical constraint equations relating to critical design requirements, (ii) the simulation is executed using these process parameters, providing predictions of the critical state variables. (iii) Constraint equation parameters are dynamically adapted using the feedback provided by the simulation predictions. This sequence is repeated until local convergence between the simulation and constraint equation predictions has been achieved. A case study in machining parameter optimization for peripheral finish milling operations is developed in which constraints on the allowable form error,Δ and the peripheral surface roughness, Ra, drive the process parameter selection for a cutting operation intended to maximize the material removal rate. Results from twenty machining scenarios are presented, including five workpiece/tool material combinations at four levels of precision. Achieving agreement (within a 5% deviation tolerance) between the simulation and constraint equation predictions required an average of 5 simulation execution cycles (maximum of 8), demonstrating promise that simulation tools can be efficiently incorporated into parameter optimization processes.
Dimensional Control of Stampings by Grid Strain Measurement
Authors: Duncan J. L. , Panton S. M. , Zhang Z-T.
Published: February 2008

This paper proposes that the dimensional control of stampings requires not only surface measurement but also measurement of the strain distribution in the part. A simple model of forming a smooth panel over a die is presented and used to show how small changes in variables such as friction can affect “shape fixability” and dent resistance. It is argued that this variability in stampings can be controlled by comparing a measured strain distribution with one specified in the design stage.
Acoustic Emission Monitoring of Tool Wear in End-Milling Using Time-Domain Averaging
Authors: Hutton D. V. , Hu F.
Published: February 2008

The characteristics of the acoustic emission signal during the tool wear process in end milling are analyzed, and a signal processing scheme for abstracting the mean time domain averaging deviation of the signal to monitor tool wear is proposed. Experiments indicate that the mean deviation value is sensitive to flank wear and its normalized value is not as dependent on milling parameters as the acoustic emission root mean square signal.
Optical Surface Analysis of the Head-Disk-Interface of Thin Film Disks
Authors: Meeks Steven W. , Weresin Walter E. , Rosen Hal J.
Published: February 2008

This paper describes the design, operation, theory, and data interpretation of an Optical Surface Analyzer (OSA). The OSA can measure carbon wear, lubricant depletion/accumulation, surface roughness, and lubricant alteration on carbon coated thin film disks. This device can measure an Angstrom of carbon wear or lubricant depletion/accumulation. The OSA can also measure debris generation and lubricant degradation through a measurement of optical index change. The lateral resolution of the OSA is approximately 5 by 10 microns and the bandwidth of the device is 2 MHz. The small device size allows it to be used within a test stand environment.
Physical Modeling and Data Analysis of the Dynamic Response of a Flexibly Mounted Rotor Mechanical Seal
Authors: Lee An Sung , Green Itzhak
Published: February 2008

The dynamic behavior of mechanical face seals has been an active area of research over the past three decades. Analytical and experimental investigations have exclusively been devoted to the flexibly mounted stator (FMS) seal. Recent theoretical work on the dynamics of the noncontacting flexibly mounted rotor (FMR) seal has proven that it excels in every aspect of dynamic behavior compared to the FMS seal. The advantages of the FMR seal, however, have to be experimentally verified. This work introduces a physical model (i.e., test rig) for an experimental investigation of the dynamic behavior of a noncontacting FMR seal. Features of the test rig, a new method of modeling and measuring the stiffness and damping of elastomeric O-ring secondary seals, and data analysis procedures will be introduced. Finally, experimental results will be compared with theory.
On the Lubrication of Short Porous Journal Bearings—Use of the Brinkman Model
Authors: Lin Jaw-Ren , Hwang Chi-Chuan
Published: February 2008

Based on the Brinkman model (MB), this paper concerns the more realistic influence of viscous shear stresses on the lubrication performance of short porous journal bearings. Compared with those using the zero pressure gradient assumption (ZPGA), the effect of LPGA provides an improvement in the bearing performance, especially when the thick-walled bearing has higher permeability parameter or the journal operates at higher eccentricity ratio.
A Method of Using Neural Networks and Inverse Kinematics for Machine Tools Error Estimation and Correction
Authors: Mou J.
Published: February 2008

A method using artificial neural networks and inverse kinematics for machine tool error correction is presented. A generalized error model is derived, by using rigid body kinematics, to describe the error motion between the cutting tool and workpiece at discrete temperature conditions. Neural network models are then built to track the time-varying machine tool errors at various thermal conditions. The output of the neural network models can be used to periodically modify, using inverse kinematics technique, the error model’s coefficients as the cutting processes proceeded. Thus, the time-varying positioning errors at other points within the designated workspace can be estimated. Experimental results show that the time-varying machine tool errors can be estimated and corrected with desired accuracy. The estimated errors resulted from the proposed methodology could be used to adjust the depth of cut on the finish pass, or correct the probing data for process-intermittent inspection to improve the accuracy of workpieces.
Flow Instability in the Orthogonal Machining of CP Titanium
Authors: Sheikh-Ahmad J. , Bailey J. A.
Published: February 2008

An experimental and analytical investigation of flow instability and shear localization in the orthogonal machining of grade 2 commercially pure titanium was made. A criterion for thermo-plastic instability was developed from torsion test results and applied to the analysis of the chip formation process. It was shown that flow instability followed by flow localization occurs when machining titanium at all cutting speeds and that a transition in the chip type from uniform to segmented does not occur. Orthogonal machining experiments were conducted in the speed range from 8.75 × 10−5 to 3.20 m/s for various depths of cut and the shear strain in the chip was calculated. It was shown that shear localization occurred in the chip formation process when the uniform shear strain involved in producing a chip segment reached a critical value and that this critical shear strain correlates fairly well with the instability shear strain predicted by the thermo-plastic instability criterion.
Material-flow Considerations for the Design of Injection Forging
Authors: Balendra R. , Qin Y.
Published: February 2008

During injection forging, the ratio of axial and radial deformation of each section of billet in the diecavity prescribes the pattern of material-flow, thereby determining the scope of the process and the quality of the product. To date, research on the quantification of the pattern of material-flow has been superficial; the models which were used invariably referred to particular conditions. FE simulation and corresponding experimental analyses were conducted with a view to characterising the flow of material during Injection Forging of solid billets and enabling the definition of the practical process range and a proposal for an approach for the design of preforms to eliminate the development of flaws.
Computational Stability Analysis of Chatter in Turning
Authors: Chen S.-G. , Ulsoy A. G. , Koren Y.
Published: February 2008

Machine tool chatter is one of the major constraints that limits productivity of the turning process. It is a self-excited vibration that is mainly caused by the interaction between the machine-tool/workpiece structure and the cutting process dynamics. This work introduces a general method which avoids lengthy algebraic (symbolic) manipulations in deriving, a characteristic equation. The solution scheme is simple and robust since the characteristic equation is numerically formulated as a single variable equation whose variable is well bounded rather than two nonlinear algebraic equations with unbounded variables. An asymptotic stability index is also introduced for a relative stability analysis. The method can be applied to other machining processes, as long as the system equations can be expressed as a set of linear time invariant difference-differential equations.
Die Life and Workpiece Properties Under Dry Condition in High-Speed Pressworking
Authors: Iwabuchi Akira , bin Hj. Yunus Ahmad , Hayashi Mitsuaki , Nishi Jun-ichiro , Sato Yuji
Published: February 2008

To explore the feasibility of “oil-free” pressworking, we investigated the effects on the life of SKD11 steel dies and the quality of phosphor bronze workpieces under lubricated and unlubricated or dry conditions. In addition, the performance of SKD11 dies coated with TiN as well as cemented tungsten carbide dies were also examined under dry conditions. Results show that the life of unlubricated SKD11 dies is about half of that under lubricated conditions. The cemented tungsten carbide die gives superior die life and workpiece quality even under dry use conditions.
Scheduling Models for Setup Reduction
Authors: Feng Chang-Xue (Jack) , Kusiak Andrew , Huang Chun-Che
Published: February 2008

The reduction of setup time has a significant impact on shortening manufacturing cycle time. In this paper, characteristics of setup activities are investigated, and models for sequencing setup activities are discussed. Sequencing setup activities can be modeled as a project scheduling problem. Two basic linear programming models for scheduling setup activities are presented. The models minimize the setup time (in particular, the internal setup time), and make a trade-off between the time and cost of setup activities with limited machining resources and budget. Factorial analysis is used to provide insights into the minimization of internal setup time.
Performance of Synthetic and Mineral Soluble Oil When Turning AISI 8640 Steel
Authors: Machado A. R. , Motta M. F. , da Silva M. B.
Published: February 2008

The present work shows a comparative study of the application of synthetic and semi synthetic, mineral soluble oil (at concentrations of 3 and 10 percent) as well as dry cut when turning AISI 8640 steel bars with triple coated (TiC,Al2O3,TiN) P35 grade of cemented carbide tools. Tool lives, cutting forces, cutting temperatures and surface roughness were considered to evaluate the cutting fluids. Generally, the semi-synthetic gave longer tool life based on flank wear parameter VB. The surface roughness was not sensitive to the lubrication quality, if wear effects are not considered. Mean tool-chip interface temperature was lower with the synthetic fluid, followed by the semi-synthetic, mineral soluble oils and dry cutting, respectively. The inverse of this order was true for the cutting forces.
A Numerical Investigation into Hot Square Die Extrusion of an L-Section Considering the Variation of Die Bearing Length
Authors: Kang Y. S. , Yang D. Y.
Published: February 2008

The variation of die bearing length is a primary way to control the metal flow in hot square die extrusion. Finite element computations are carried out to assess the influences of die bearing on metal flow and state variables. The finite element analysis is presented based on the arbitrary Lagrangian-Eulerian (ALE) description for a rigid-viscoplastic material. Since the thermal state greatly affects the product quality, temperature distribution is also analyzed. In order to estimate the varied lengths of die bearing, a numerical scheme is suggested and demonstrated through the simulation of an industrial example with varied die bearing. The computational results for extrusion with varied die bearing are compared with those from the simulation for extrusion with constant die bearing.
The Influence of Friction-Speed Relation on the Occurrence of Stick-Slip Motion
Authors: You Hsien-I , Hsia Jeng-Hong
Published: February 2008

A theoretical study of stick-slip motion is provided in the present paper. The study focuses on the influence of the friction-speed relation and the effects of driving speed and damping force of the system on the behavior of the stick-slip motion. The two latter effects are characterized by the speed parameter, Sp, and the damping ratio,ξ, respectively. The results show that, for a system undergoing nonuniform motion, the vibratory frequency increases and the amplitude decreases as the speed parameter increases. For two contacting sliding surfaces, there exists an inversion state at which the stick-slip motion disappears. The magnitude of the negative slope of the friction-speed relation near Vr = 0 is shown to have significant effect on the occurrence of the stick-slip motion.
New Class of Sliders Numerically Designed for Maximum Stiffness
Authors: Robert M. P.
Published: February 2008

The following inverse problem is addressed: given a class of slider geometry for which the gap can only have two values and given its global footprint, where should one distribute the etching (or deposition) of the air bearing surface such that the corresponding stiffness is maximum? First, this optimization problem is mathematically setup and formulated. Then, a simple numerical algorithm is proposed which will generate the desired gap profile, the method is based on an iterative approach on the unknown gap distribution coupled with a finite element solution of the pressure solution. Finally, the canonical example of a simple square slider is treated for various stiffnesses (normal, pitch, roll and mixed modes), and the results illustrate the proposed technique.
A Simplified Direct Method for Cyclic Strain Calculation: Repeated Rolling/Sliding Contact on a Case-Hardened Half Plane
Authors: Yu C.-C. , Moran B. , Keer L. M.
Published: February 2008

A direct analysis method for problems in repeated elastic-plastic rolling/sliding contact is presented. The method is shown to be an efficient technique for the determination of the steady-state solution under proportional or nonproportional cyclic loading and can provide such results as residual stress, residual strain, and cyclic strain range. Furthermore, the method is valid for both elastic and plastic shakedown. A two-dimensional rolling/sliding contact problem is considered with emphasis on the calculation of cyclic plastic strains. Several numerical techniques are employed to simplify and reduce the computational effort. These techniques consist of an operator split, the modified incremental projection method, middle-loading state, and decomposition into residual steady-state and cyclic parts. The resulting scheme is highly efficient and is ideally suited for parameter studies. To demonstrate the practical application of the approach, a two-dimensional contact problem, assuming a case-hardened material, is solved.
On the Physical Meanings of Λ/Q˜p0 and σ/Q˜p0 in Molecular Gas Film Lubrication Problems
Authors: Fukui S. , Matsuda R. , Kaneko R.
Published: February 2008

To estimate molecular gas film lubrication (MGL) characteristics, we propose a modified bearing number Λ′ and a modified squeeze number σ′, which are, respectively, the conventional bearing Λ and squeeze number σ divided by the relative Poiseuille flow rate Q˜p0. Using Λ′ and σ′, the linearized MGL problem can be reduced to the continuum gas film lubrication problem and the MGL characteristics can be exactly estimated, if the characteristic flow rate corresponding to the spacing, Q˜p0, is known. For nonlinear MGL problems, the lubrication characteristics can be verified to be roughly estimated by Λ′ and σ′ both in rectangular slider bearings and in circular squeeze-film thrust bearings.
Readback Signal Decrease Due to Dynamic Load Head-Disk Contacts
Authors: Fu Ta-Chang , Bogy D. B.
Published: February 2008

The effect of head-disk impacts due to repeated dynamic load is investigated experimentally. Loading conditions more severe than those typically found in ramp-load disk drives are applied to ensure that contacts occur, and disk-synchronized head loading motions are applied so that the head-disk contact points are all distributed within a small area on the disk. The resulting readback signal decrease was observed to correlate with the head-disk impact velocity and hence the slider’s vertical approaching velocity. With a larger vertical velocity, readback signal decrease appeared earlier and the amount of decrease was larger. The results indicate that dynamic load-unload should be quite reliable under typical loading conditions, and the reliability of dynamic load-unload can be achieved by controlling the vertical approaching velocity of the slider. This is comparatively easier than controlling the narrow manufacturing tolerances of the slider’s pitch and roll of the head-suspension assembly. The technological trend toward using smaller-sized head-suspension assemblies and higher-coercivity magnetic disks may further enhance the dynamic load head-disk interface durability.
Ultrathin Liquid Lubrication of Magnetic Head-Rigid Disk Interface for Near-Contact Recording: Part I—A Closed-Form Solution to the Reynolds Equation
Authors: Hsiao Hsing-Sen S. , Bhushan Bharat , Hamrock Bernard J.
Published: February 2008

A closed-form approximate solution to ultrathin and near-zero-pitch liquid lubrication of magnetic head-rigid disk interfaces for near-contact recording is derived. This study focuses on the steady state at the fully flooded rail-disk contact condition. It is assumed that the lubricant in the interface is isoviscous and the slider is in the no-roll and no-yaw situation. Simple dimensionless groups of operating factors are identified to facilitate the parametric study of performance. Results of interface geometry effects on load, location of pressure center, friction force, and friction coefficient are presented. Typical distributions of pressure and shear stress at rail surface are also presented. The important effects such as shear thinning and thermal thinning are incorporated by introducing shear thinning and thermal thinning factors. Implementation of these correction factors will be presented in Part II.
Design Optimization of the Taper-Flat Slider Positioned by a Rotary Actuator
Authors: Yoon Sang-Joon , Choi Dong-Hoon
Published: February 2008

In this paper, an optimization technique is utilized to find an optimum configuration of the taper-flat slider positioned by a rotary actuator for enhanced static air-bearing characteristics. The aim of optimization consists in simultaneously minimizing the variation in flying height from a target value, maximizing the smallest pitch angle, and minimizing the largest roll angle, over the entire magnetic recording band. As the design variables, the leading edge taper angle and rail width of a taper-flat slider, and the skew angle at the inside track are chosen since they seem to be the most influential parameters on air-bearing characteristics. The optimum design variables are automatically obtained by using the augmented Lagrange multiplier method, and the static characteristics of the optimally designed sliders are found to be superior to those of the taper-flat sliders of typical configuration over the entire recording band. Results obtained for three taper-flat slider models are reported, showing the effectiveness of the proposed design scheme.
Nanoscale Indentation Hardness and Wear Characterization of Hydrogenated Carbon Thin Films
Authors: Wei B. , Komvopoulos K.
Published: February 2008

An experimental investigation of the surface topography, nanoindentation hardness, and nanowear characteristics of carbon thin films was conducted using atomic force and point contact microscopy. Hydrogenated carbon films of thickness 5, 10, and 25 nm were synthesized using a sputtering technique. Atomic force microscopy images obtained with silicon nitride tips of nominal radius less than 20 nm demonstrated that the carbon films possessed very similar surface topographies and root-mean-square roughness values in the range of 0.7–1.1 nm. Nanoindentation and nanowear experiments performed with diamond tips of radius equal to about 20 nm revealed a significant enhancement of the hardness and wear resistance with increasing film thickness. High-resolution surface imaging indicated that plastic flow was the dominant deformation process in the nanoindentation experiments. The carbon wear behavior was strongly influenced by variations in the film thickness, normal load, and number of scanning cycles. For a given film thickness, increasing the load caused the transition from an atomic-scale wear process, characterized by asperity deformation and fracture, to severe wear consisting of plowing and cutting of the carbon films. Both the critical load and scanning time for severe wear increased with film thickness. Below the critical load, the wear rate decreased with further scanning and the amount of material worn off was negligibly small, while above the critical load the wear rate increased significantly resulting in the rapid removal of carbon. The observed behavior and trends are in good qualitative agreement with the results of other experimental and contact mechanics studies.
Stability of Rough Journal Bearings Using Nonlinear Transient Method
Authors: Ramesh J. , Majumdar B. C.
Published: February 2008

The stability of rigid rotors supported on finite oil rough journal bearings has been investigated using nonlinear transient method. The effect of various surface roughness parameters, viz., composite surface roughness, roughness orientation pattern, variance ratio on the stability is presented in the form of journal center trajectories. Although the stability is affected marginally with the increase in composite roughness, the variation is quite significant when the shear flow factor comes into the picture.
Force Coefficients for a Centrally Grooved Short Squeeze Film
Damper
Authors: Zhang J. X. , Roberts J. B.
Published: February 2008

A centrally grooved short squeeze film damper (SFD), together with its lubricant supply mechanism (LSM), is analyzed, using an integrated theoretical model. It is shown that the traditional analysis for such a damper, where the effects of the central groove and the LSM are ignored, can lead to a seven-fold underestimation of the magnitude of the hydrodynamic force coefficients. The new theory gives predictions for the damping coefficients which are in good agreement with corresponding experimental results. Moreover, a five-fold improvement is obtained for both the temporal and convective inertia coefficients, at low values of eccentricity. The new model leads to the prediction of a nonzero fluid static force which, in conformity with experimental results, is linearly related to the supply pressure. The existence of this static force has not been explained by previous theoretical work on SFDs.
Enhanced Wear Performance of Transformation Toughened Ceramics by Microstructural Optimization
Authors: Thomsen N. B. , Karihaloo B. L.
Published: February 2008

The poor rolling/sliding wear performance of transformation toughened ceramics (TTC) such as partially stabilized zirconia (PSZ) is believed to be a result of the volume expansion accompanying phase transformation of precipitates located immediately beneath the contacting surface. The expanding precipitates induce a surface uplift leading to surface waviness and altered rolling/sliding conditions. The very same precipitates, on the other hand enhance the toughness of the ceramic by preventing the growth of surface cracks. In order to find a compromise solution, an optimization problem is formulated for an idealized model consisting of an edge crack normal to the contacting surface and a periodic distribution of transformable grains in the layer immediately beneath this surface. The objective is to maximize the crack tip shielding by varying the volume fraction and size of the layer without exceeding a prescribed allowable surface uplift. It is shown that the maximum volume fraction of t-ZrO2 is attained at a certain depth below the surface but that its magnitude is considerably smaller than that pertaining in peak-aged PSZ.