bluuebunny/crossref_metadata_2025 huggingface dataset:
Authenticity in leadership: an emerging perspective
Authors: Duignan Patrick A. , Bhindi Narottam
Published: July 2002

First describes the current context of cynicism about the quality and integrity of many of our leaders in contemporary public and private sector organizations and the culture of “artifice” prevailing in many of these organizations. Then presents a conceptual framework for authenticity in leadership in organizations. The elements of the framework include: the need to identify “authentic self” in terms of significant values and relationships; the centrality of authentic relationships to effective leadership; the need in organizations for conditions for authentic learning; the way in which governance and organization can facilitate or inhibit authentic relationships and learning. Proposes a leadership praxis which links the theory, practice and ethics of leadership, responds to many of the concerns about the lack of honesty and integrity in leadership, and acts as a counterbalance to the artifice and deception prevalent in leadership in many contemporary organizations.
The development of Richard Bates’s critical theory in educational administration
Authors: Hyung Park Sun
Published: July 2002

For nearly two decades, in the field of educational administration, Bates’s critical theory has been one of the most vigorous challenges to the value neutral approach of traditional theories. He has been a key voice claiming that such theories are ideological and mainly concerned with protecting vested interests and class divisions in society. Despite their theoretical endurance and practical implications, the main ideas advocated by Bates’s critical theory have not been examined seriously in the field. This paper analyses the main ideas of Bates’s critical social theory in three ways. First, the major intellectual influences that shaped Bates’s theory are examined. Second, those areas where Bates and Greenfield shared similar views yet took different approaches are considered. Finally, the main arguments that critics raised against Bates are examined and evaluated.
Hydromagnetic combined heat and mass transfer by natural convection from a permeable surface embedded in a fluid‐saturated porous medium
Authors: Chamkha Ali J. , Khaled Abdul‐Rahim A.
Published: July 2002

The problem of coupled heat and mass transfer by natural convection from a vertical, semi‐infinite flat plate embedded in a porous medium in the presence of an external magnetic field and internal heat generation or absorption effects is formulated. The plate surface is maintained at either constant temperature or constant heat flux and is permeable to allow for possible fluid wall suction or blowing. The resulting governing equations are non‐dimensionalized and transformed using a non‐similarity transformation and then solved numerically by an implicit, iterative, finite‐difference scheme. Comparisons with previously published work are performed and excellent agreement is obtained. Useful correlations containing the various physical parameters for both isothermal and isoflux wall conditions are reported. A parametric study of all involved parameters is conducted and a representative set of numerical results for the velocity, temperature and concentration profiles as well as the skin‐friction parameter, Nusselt number, and the Sherwood number is illustrated graphically to show typical trends of the solutions.
Natural convection in enclosures with localized heating from below and symmetrical cooling from sides
Authors: Aydin Orhan , Yang Wen‐Jei
Published: July 2002

Natural convection of air in a two‐dimensional, rectangular enclosure with localized heating from below and symmetrical cooling from the sides has been numerically investigated. Localized heating is simulated by a centrally located heat source on the bottom wall, and four different values of the dimensionless heat source length, 1/5, 2/5, 3/5 and 4/5 are considered. Solutions are obtained for Rayleigh number values from 103 to 106. Local results are presented in the form of streamline and isotherm plots as well as the variation of local Nusselt number on the heated wall. Finally, the average Nusselt number at the heated part of the lower wall, \overline Nu, was shown to increase with an increase the Rayleigh number, Ra, or of the nondimensional heat source thickness, ε.
A one‐dimensional finite element simulation for the fire‐performance of GRP panels for offshore structures
Authors: Looyeh M.R.E. , Bettess P. , Gibson A.G.
Published: July 2002

A one‐dimensional finite element model, associated with a computer code, has been developed to simulate the thermal response of a decomposing glass‐fibre reinforced composite exposed to a fire environment. The numerical model uses a first‐order Arrhenius equation and includes: transient heat conduction; gas mass flux and internal heat convection of decomposition gases; density loss and Arrhenius decomposition of active material into decomposition gases and residual char; and endothermicity of the decomposition process. An empirical formula, obtained from furnace tests, has been applied to the model as the incident heat flux boundary condition at the heated surface. Presents results for the standard thickness of polyester‐based GRP laminate, 10.9mm, for offshore structures. The predicted temperature profiles are in good agreement with experimental temperatures obtained from furnace tests. This model is able to simulate fire performance characteristics for a large range of typical offshore components with different constructions and materials. It will enable accurate predictions of the life‐time of offshore components in severe offshore hydrocarbon fires.
An integrated CAD system for design of heterogeneous objects
Authors: Bhashyam Srinivas , Hoon Shin Ki , Dutta Debashish
Published: July 2002

Computer aided design systems are routinely used by designers for creating part geometries. Interfaces to computer aided analysis and manufacturing are also commonplace enabling the rapid fabrication of the designed part. Thus far, however, the focus was on objects with homogeneous interior. Two recent advances use of functionally graded materials in parts, and layered manufacturing technology have brought to the forefront the need for CAD systems to support the creation of geometry as well as the graded material inside. This paper reports on such a system. We describe the need, the components and implementation of a CAD system for creating heterogeneous objects. Two examples illustrate the use.
Optimal orientation with variable slicing in stereolithography
Authors: Xu F. , Wong Y.S. , Loh H.T. , Fuh J.Y.H. , Miyazawa T.
Published: July 2002

Accuracy and building time are two important concerns in rapid prototyping (RP). Usually there exists a trade‐off between these two aspects pertaining to model building in RP. The use of variable thickness slicing can satisfy these two requirements to some extent. Introduces an adaptive variable thickness slicer implemented on a solid CAD modeller. The slicer employs a genetic algorithm to find the minimum layer thickness allowed at referenced height with a given cusp height tolerance. By introducing the variable thickness slicing technique, the optimal orientation for part building in RP systems is considered. Seeks to obtain the optimal orientation with adaptive slicing for part building in stereolithography (SLA) systems. Takes into consideration building time, accuracy and stability of the part when determining the optimal orientation. Results show that the proposed approach gives an effective and practical solution for building parts with curved surfaces.
Considerations and selection of optimal orientation for different rapid prototyping systems
Authors: Xu F. , Loh H.T. , Wong Y.S.
Published: July 2002

The ability to evaluate and determine the best part building orientation for different rapid prototyping (RP) processes is important for building a satisfactory part/prototype within the limits of manufacturing time and building cost. It is also an essential step towards the identification of the most suitable RP process with a given RP application. This paper discusses the selection of building direction for four RP processes, namely stereolithography (SL), selective laser sintering (SLS), fusion deposition modelling (FDM) and laminated object manufacturing (LOM). Main differences in the four processes are first examined with emphasis on the effects of these differences with regard to the building inaccuracy, the surface finish, the manufacturing time and cost. An optimal orientation algorithm is demonstrated on a part considered for processing with one of the four RP processes. The influence of the process characteristics on the selection of appropriate orientation with different RP processes is illustrated in the example.
Understanding thermostability in cytochrome P450 by combinatorial mutagenesis
Authors: Maves Shelley A. , Sligar Stephen G.
Published: July 2002

The cytochromes P450 are an important class of mono‐oxygenases involved in xenobiotic metabolism and steroid biosynthesis in a diverse set of life forms. Discovery of CYP‐119, a P450 from the archea Sulfolobus solfataricus has provided a means for understanding nature's method of stabilizing this important protein superfamily. To identify classes of stabilizing interactions used by CYP‐119, we have generated a randomized library of point mutants and screened for mutants that are less thermostable than the wild type by monitoring the characteristic Soret band in the visible region of the cell lysis. The selected mutants were characterized by differential scanning calorimetry to compare the temperatures of the melting transitions of the various mutants. The identified mutations suggested that electrostatic interactions involving salt links and charge–charge interactions, as well as contributions from other interactions such as aromatic stacking, and side chain volume of hydrophobic residues contribute to enhanced thermostability in this cytochrome P450.
Distribution and behaviour of glabrous cutaneous receptors in the human foot sole
Authors: Kennedy Paul M. , Inglis J. Timothy
Published: July 2002

To document the activity of cutaneous mechanoreceptors in the glabrous skin of the foot sole, tungsten microelectrodes were inserted through the popliteal fossa and into the tibial nerve of thirteen healthy human subjects. A total of 104 cutaneous mechanoreceptors were identified in the glabrous skin of the foot. This sample consisted of 15 slow adapting type I (14 %), 16 slow adapting type II (15 %), 59 fast adapting type I (57 %), and 14 fast adapting type II units (14 %). The location of the receptors and the outline of the receptive fields were determined by using nylon monofilaments perpendicularly applied against the surface of the skin. This revealed that the receptors were widely distributed without an accumulation of receptors in the toes. There were also larger receptive fields predominantly isolated on the plantar surface of the metatarsal‐tarsal region of the foot sole. Furthermore, with the foot in an unloaded position, there was no background discharge activity in any of the cutaneous receptors in the absence of intentionally applied stimulation. These findings suggest that skin receptors in the foot sole behave differently from those receptors found on the glabrous skin of the hand. This may reflect the role of foot sole skin receptors in standing balance and movement control.
Regulation of the glutamine transporter SN1 by extracellular pH and intracellular sodium ions
Authors: Bröer Angelika , Albers Alexandra , Setiawan Iwan , Edwards Robert H. , Chaudhry Farrukh A. , Lang Florian , Wagner Carsten A. , Bröer Stefan
Published: July 2002

The glutamine transporter SN1 has recently been identified as one of the major glutamine transporters in hepatocytes and brain astrocytes. It appears to be the molecular correlate of system N amino acid transport. Two different transport mechanisms have been proposed for this transporter. These are an electroneutral mechanism, in which glutamine uptake is coupled to an exchange of 1Na+ and 1H+, or an electrogenic mechanism coupled to the exchange of 2Na+ against 1H+. This study was performed to solve these discrepancies and to investigate the reversibility of the transporter. When SN1 was expressed in Xenopus laevis oocytes, glutamine uptake was accompanied by a cotransport of 2–3 Na+ ions as determined by 22Na+ fluxes. However, at the same time a rapid release of intracellular Na+ was observed indicating an active exchange of Na+ ions. The driving force of the proton electrochemical gradient was equivalent to that of the sodium electrochemical gradient. Acidification of the extracellular medium caused the transporter to run in reverse and to release glutamine. Determination of accumulation ratios at different driving forces were in agreement with an electroneutral 1Na+‐glutamine cotransport‐1H+ antiport. Inward currents that were observed during glutamine uptake were much smaller than expected for a stoichiometric cotransport of charges. A slippage mode in the transporter mechanism and pH‐regulated endogenous oocyte cation channels are likely to contribute to the observed currents.
Hybrid Vibration Absorption by Zero/Pole-Assignment
Authors: Yuan Jing
Published: July 2002

This paper presents a hybrid dynamic vibration absorber (HDVA) that is able to assign tunable zeros and poles to a closed-loop primary system. A detailed procedure is presented to design the HDVA and match closed-loop response of a primary system to a prototype transfer function, subject to a modest constraint that the prototype is minimum-phase with relative degree 2. [S0739-3717(00)00103-3]
Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part I—Analytical Results
Authors: Akalin Ozgen , Newaz Golam M.
Published: July 2002

An axi-symmetric, hydrodynamic, mixed lubrication model has been developed using the averaged Reynolds equation and asperity contact approach in order to simulate frictional performance of piston ring and cylinder liner contact. The friction force between piston ring and cylinder bore is predicted considering rupture location, surface flow factors, surface roughness and metal-to-metal contact loading. A fully flooded inlet boundary condition and Reynolds boundary conditions for cavitation outlet zone are assumed. Reynolds boundary conditions have been modified for non-cavitation zones. The pressure distribution along the ring thickness and the lubricant film thickness are determined for each crank angle degree. Predicted friction force is presented for the first compression ring of a typical diesel engine as a function of crank angle position.
Analysis and Control of Multi-Mode Axial Flow Compression System Models1
Authors: Xiao MingQing , Bas¸ar Tamer
Published: July 2002

The paper studies the behavior of multi-mode systems of the Moore-Greitzer model. Its main result is the existence of a parameterized nonlinear state feedback controller which stabilizes the system to the right of the peak of the compressor characteristic. In this process, a rotating stall envelope surface is discovered, and it is shown that the controller design achieves the tasks of preventing the closed-loop system from entering either rotating stall or surge, and making the closed-loop pressure rise coefficient be able to approach its maximum. Numerical simulations of the open-loop and closed-loop models are presented to illustrate the analysis and the results. [S0022-0434(00)00803-0]
Design of an Overconstrained and Dextrous Spherical Wrist
Authors: Wiitala Jared M. , Stanisˇic´ Michael M.
Published: July 2002

A new dextrous spherical wrist is presented here. The wrist is based upon a kinematically overconstrained and singularity-free pointing system. The pointing system and wrist are less mechanically complicated and have simpler kinematics than previously proposed systems. The mechanical simplification has enabled construction of a prototype, shown in photographs. [S1050-0472(00)00603-6]
Combustion Instabilities in Industrial Gas Turbines—Measurements on Operating Plant and Thermoacoustic Modeling
Authors: Hobson David E. , Fackrell John E. , Hewitt Gary
Published: July 2002

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150 MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analyzed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits. A theoretical model of the thermoacoustic behavior of the combustion system has been developed to see to what extent the observed behavior on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterized simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics. The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics. [S0742-4795(00)01403-4]
DSP Implementation of an Active Bearing Mount for Rotors Using Hybrid Control
Authors: Bai Mingsian R. , Luo Weibin
Published: July 2002

An on-line active technique for suppressing rotor vibration is proposed. Electromagnetic actuators are mounted on the housing of a ball bearing for generating counter forces to cancel the transverse vibrations due to imbalance, misalignment, and so forth. Controllers based on feedback structure, feedforward structure and hybrid structure are investigated. The multiple channel active control systems are implemented on the platform of a digital signal processor. Numerical simulation and experimental investigations indicate that the proposed methods are effective in suppressing the periodic disturbances. In particular, the hybrid control by using feedback linear quadratic gaussian control and feedforward least mean square algorithm with synthetic reference achieves the best performance in terms of vibration attenuation and convergence speed. [S0739-3717(00)00904-1]
Energetics and Stability of Translating Media with an Arbitrarily Varying Length
Authors: Zhu W. D. , Ni J.
Published: July 2002

The linear dynamics of a class of translating media with an arbitrarily varying length is investigated. The tension in the media arising from their longitudinal accelerations is incorporated. The dynamic stability of the continuous media relative to the inertial and moving coordinate systems is studied from the energy standpoint. The exact expressions for the rates of change of energies of media are derived and interpreted from both control volume and system viewpoints. The stability analyses relative to the inertial and moving coordinate systems result in the same predictions. Examples including a robotic arm through a prismatic joint and an elevator cable in a high-rise building illustrate the analysis. In particular, the results explain an inherent “unstable shortening cable behavior” encountered in elevator industry. [S0739-3717(00)00503-1]
Unsteady Laminar Duct Flow With a Given Volume Flow Rate Variation
Authors: Das D. , Arakeri J. H.
Published: July 2002

In this paper we give a procedure to obtain analytical solutions for unsteady laminar flow in an infinitely long pipe with circular cross section, and in an infinitely long two-dimensional channel, created by an arbitrary but given volume flow rate with time. In the literature, solutions have been reported when the pressure gradient variation with time is prescribed but not when the volume flow rate variation is. We present some examples: (a) the flow rate has a trapezoidal variation with time, (b) impulsively started flow, (c) fully developed flow in a pipe is impulsively blocked, and (d) starting from rest the volume flow rate oscillates sinusoidally. [S0021-8936(00)01702-5]
Micromechanics of Hysteresis Loops of Fatigue in a Single Crystal
Authors: Lin T. H. , Wong K. K. F. , Teng N. J.
Published: July 2002

Grain boundaries are susceptible to cause boundary corrosion, cracking, and creep deformation. Single crystals are presently used in turbine engines. A micromechanic analysis is shown to explain the occurrence of highly localized plastic strain in the slip band known as the shear band in metals under a monotonic loading. Based on the prior analyses of fatigue bands in polycrystals, a micromechanic analysis of a single crystal under plane deformation is developed. The Bauschinger effect and hysteresis loops of these single crystals were calculated and shown. The calculated results agree generally with experimental observations. [S0021-8936(00)02202-9]
Elastohydrodynamics of a Worm Gear Contact
Authors: Kong S. , Sharif K. , Evans H. P. , Snidle R. W.
Published: July 2002

The paper is concerned with prediction of elastic contact and elastohydrodynamic film thickness in worm gears. Using the undeformed geometry of the gap between gear teeth in contact a three-dimensional elastic contact simulation technique has been developed for calculation of the true area of elastic contact under load relative to the wheel and worm surfaces. A parallel investigation of elastohydrodynamic lubrication effects has been carried out using a special non-Newtonian, thermal solver which takes account of the nonsymmetrical and spin aspects of worm contacts. An interesting feature of the results obtained is the discovery of regions of poor film forming due to entrainment failure at the edges of the contact.
Physically Based Modeling of Reciprocating Lip Seal Friction
Authors: Wassink Dirk B. , Lenss Viesturs G. , Levitt Joel A. , Ludema Kenneth C.
Published: July 2002

Lip seal friction under constant speed sliding is modeled as the sum of three physically based components: (1) viscous shear loss in the lubricant; (2) hysteresis losses due to roughness-imposed deformation of the seal material, and (3) hysteresis losses due to deformation caused by varying intermolecular forces at the sliding interface. Increasingly thick hydrodynamic films progressively reduce contributions of the roughness and intermolecular components. Peaks in friction expected from these two components are smaller, occurring at lower sliding speed, than in “dry” rubber friction. Model simulations capture friction trends with temperature, hydraulic pressure, seal material, lubricant viscosity and shaft roughness.
Three-Dimensional Analytical Solution for Hybrid Multilayered Piezoelectric Plates
Authors: Vel S. S. , Batra R. C.
Published: July 2002

Analytical solutions for the static three-dimensional deformations of multilayered piezoelectric rectangular plates are obtained by using the Eshelby-Stroh formalism. The laminated plate consists of homogeneous elastic or piezoelectric laminae of arbitrary thicknesses. The equations of static, linear, piezoelectricity are exactly satisfied at every point in the body. The analytical solution is in terms of an infinite series; the continuity conditions at the interfaces and boundary conditions at the edges are used to determine the coefficients. The formulation admits different boundary conditions at the edges and is applicable to thick and thin laminated plates. Results are presented for thick piezoelectric plates with two opposite edges simply supported and the other two subjected to various boundary conditions. [S0021-8936(00)01803-1]
Phase Structure and Cyclic Deformation in Eutectic Tin-Lead Alloy: A Numerical Analysis
Authors: Shen Y.-L. , Li W. , Fang H. E.
Published: July 2002

This study is devoted to providing a mechanistic rationale of coarsening induced failure in solder alloys during thermomechanical fatigue. Micromechanical modeling of cyclic deformation of eutectic tin-lead alloy was undertaken using the finite element method. The models consist of regularly arranged tin-rich and lead-rich phases, simulating the lamellar array and colony structure in a typical eutectic system. A fine structure and a coarse structure, bearing the same phase fraction but different in the aspect ratio of each lead-rich layer and in the number of lead-rich layers in each colony, are utilized for representing the microstructure before and after coarsening, respectively. Both phases are treated as elastic–plastic solids with their respective properties. For simplicity the creep effect is ignored without compromising the main objective of this study. Cyclic loading under pure shear and uniaxial conditions is modeled. It is found that both the fine and coarse structures exhibit essentially the same macroscopic stress–strain response. The coarse structure, however, shows a greater maximum effective plastic strain on a local scale throughout the deformation. The numerical result implies that, in a solder joint, a locally coarsened region may not be mechanically weaker than its surrounding, but it is subject to early damage initiation due to accumulated plasticity. Other implications regarding solder alloy failure and micromechanical modeling of two-phase materials are discussed.
Comparative Studies on Short and Long Length-Scale Stall Cell Propagating in an Axial Compressor Rotor
Authors: Inoue M. , Kuroumaru M. , Tanino T. , Yoshida S. , Furukawa M.
Published: July 2002

In a low-speed compressor test rig at Kyushu University, multiple short length-scale stall cells appeared under a mild stall condition and turned into a long length-scale cell under a deep stall condition. Then, for the two types of stall cell, the pressure distribution on the casing wall and the velocity distributions upstream and downstream of the rotor have been measured by high-response pressure transducers and a slanted hot-wire, respectively. The time-dependent ensemble-averages of these distributions have been obtained phase-locked to both the rotor and the stall cell rotation using a “double phase-locked averaging technique” developed by the authors. The structures of the two stall cells are compared: The short length-scale stall cell is characterized by a concentrated vortex spanning from the casing wall ahead of the rotor to the blade suction surface. In the long length-scale stall cell, the separation vortices go upstream irregularly when blade separation develops in the front half of the cell, and re-enter the rotor on the hub side in the rear half of it. The unsteady aerodynamic force and torsional moment acting on the blade tip section have been evaluated from the time-dependent ensemble-averages of the casing wall pressure distribution. The force fluctuation due to the short length-scale cells is somewhat smaller than that for the long length-scale cell. The blade suffers two peaks of the force during a period of the short length-scale cells passing through it. The moment fluctuation for the short length-scale cells is considerably larger than that for the long length-scale cell.
Rheological Properties of Polyolester Under an EHD Contact in Some Refrigerant Environments
Authors: Muraki Masayoshi , Sano Takashi , Dong Daming
Published: July 2002

EHD traction of polyol ester in some refrigerants is analyzed using the non-Newtonian theory, from which available rheological parameters are determined. Then the rheological parameters are studied in elation to refrigerant concentration. As a result, the viscosity pressure coefficient of the mixtures is inversely correlated with refrigerant concentration in terms of mole per volume, while the representative stress characterizing the non-Newtonian is positively correlated. When the viscous volume relating to the unit of viscous flow is plotted as a function of molecular volume of refrigerant/POE mixture, the relation between them is well described by a single line independent of kinds of refrigerants.
Transient Elastic Thermal Stress Development During Laser Scribing of Ceramics
Authors: Modest Michael F. , Mallison Thomas M.
Published: July 2002

Lsaers are emerging as a valuable tool for shaping and cutting hard and brittle ceramics. Unfortunately, the large, concentrated heat flux rates that allow the laser to efficiently cut and shape the ceramic also result in large localized thermal stresses in a small heat-affected zone. These notable thermal stresses can lead to micro-cracks, a decrease in strength and fatigue life, and possibly catastrophic failure. In order to assess where, when, and what stresses occur during laser scribing, an elastic stress model has been incorporated into a three-dimensional scribing and cutting code. First, the code predicts the temporal temperature fields and the receding surface of the ceramic. Then, using the scribed geometry and temperature field, the elastic stress fields are calculated as they develop and decay during the laser scribing process. The analysis allows the prediction of stresses during continuous wave and pulsed laser operation, a variety of cutting speeds and directions, and various shapes and types of ceramic material. The results of the analysis show substantial tensile stresses develop over a thick layer below and parallel to the surface, which may be the cause of experimentally observed subsurface cracks.
Local Dynamic Stability Versus Kinematic Variability of Continuous Overground and Treadmill Walking
Authors: Dingwell J. B. , Cusumano J. P. , Cavanagh P. R. , Sternad D.
Published: July 2002

This study quantified the relationships between local dynamic stability and variability during continuous overground and treadmill walking. Stride-to-stride standard deviations were computed from temporal and kinematic data. Maximum finite-time Lyapunov exponents were estimated to quantify local dynamic stability. Local stability of gait kinematics was shown to be achieved over multiple consecutive strides. Traditional measures of variability poorly predicted local stability. Treadmill walking was associated with significant changes in both variability and local stability. Thus, motorized treadmills may produce misleading or erroneous results in situations where changes in neuromuscular control are likely to affect the variability and/or stability of locomotion.
Parametric Instability of Axially Moving Media Subjected to Multifrequency Tension and Speed Fluctuations
Authors: Parker R. G. , Lin Y.
Published: July 2002

This work investigates the stability of axially moving media subjected to parametric excitation resulting from tension and translation speed oscillations. Each of these excitation sources has spectral content with multiple frequencies and arbitrary phases. Stability boundaries for primary parametric instabilities, secondary instabilities, and combination instabilities are determined analytically through second-order perturbation. The classical result that primary instability occurs when one of the excitation frequencies is close to twice a natural frequency changes as a result of multiple excitation frequencies. Unusual interactions occur for the practically important case of simultaneous primary and secondary instabilities. While sum type combination instabilities occur, no difference type instabilities are detected. The nonlinear limit cycle amplitude that occurs under primary instability is derived using the method of multiple scales.
Modeling and Simulation Methods for Design of Engineering Systems
Authors: Sinha Rajarishi , Paredis Christiaan J. J. , Liang Vei-Chung , Khosla Pradeep K.
Published: July 2002

This article presents an overview of the state-of-the art in modeling and simulation, and studies to which extent current simulation technologies can effectively support the design process. For simulation-based design, modeling languages and simulation environments must take into account the special characteristics of the design process. For instance, languages should allow models to be easily updated and extended to accommodate the various analyses performed throughout the design process. Furthermore, the simulation software should be well integrated with the design tools so that designers and analysts with expertise in different domains can effectively collaborate on the design of complex artifacts. This review focuses in particular on modeling for design of multi-disciplinary engineering systems that combine continuous time and discrete time phenomena.
Experimental and Numerical Investigation of Two-Dimensional Parallel Jets
Authors: Anderson Elgin A. , Spall Robert E.
Published: July 2002

The flowfield of dual, parallel planar turbulent jets is investigated experimentally using an x-type hot-wire probe and numerically by solving the Reynolds-averaged Navier-Stokes equations. The performance of both differential Reynolds stress (RSM) and standard k-ε turbulence models is evaluated. Results show that the numerical models predict the merge and combined point characteristics to good accuracy. However, both turbulence models show a narrower width of the jet envelope than measured by experiment. The predicted profiles of the mean velocity along the symmetry plane agree well with the experimental results.
Design of Capacitance Probes for Oil Film Thickness Measurements Between the Piston Ring and Linear in Internal Combustion Engines
Authors: Ducu D. O. , Donahue R. J. , Ghandhi J. B.
Published: July 2002

Measurement of the capacitance formed between the piston ring and a probe mounted in the cylinder liner provides an accurate means of determining the oil film thickness provided that the region between the ring and probe is flooded with oil and the dielectric constant of the oil is known. All aspects of the design, construction, installation of capacitance probes, and analysis of the resulting measurements are reviewed in this paper. Biases introduced due to the fringing of the electric field, curvature of the ring face profile, roughness of the ring profile, and the tilt angle of the ring face are analyzed, and correction algorithms are proposed. Errors associated with the proposed algorithms are gauged through comparisons to finite difference solutions. Shielding the sensing electrode is found to eliminate fringing effects and also stray capacitance which can affect the signal. A rectangular probe design with a high aspect ratio is suggested as an optimum. The small axis of the probe provides high spatial resolution, while the longer length, which is in the circumferential direction, provides a sufficient surface area to ensure sufficient signal strength. A design procedure which allows for the sizing of probe dimensions for a given level of allowable error and capacitance measuring circuitry is developed.
Aerodynamic Performance of a Transonic Turbine Cascade at Off-Design Conditions
Authors: Jouini D. B. M. , Sjolander S. A. , Moustapha S. H.
Published: July 2002

The paper presents detailed measurements of the midspan aerodynamic performance of a transonic turbine cascade at off-design conditions. The measurements were conducted for exit Mach numbers ranging from 0.5 to 1.2, and for Reynolds numbers from 4×105 to 106. The profile losses were measured for incidence values of +14.5 deg, +10 deg, +4.5 deg, 0 deg, and −10 deg relative to design. To aid in understanding the loss behavior and to provide other insights into the flow physics, measurements of blade loading, exit flow angles, trailing-edge base pressures, and the axial velocity density ratio (AVDR) were also made. It was found that the profile losses at transonic Mach numbers can be closely related to the base pressure behavior. The losses were also affected by the AVDR.
Effect of Stator Design on Stator Boundary Layer Flow in a Highly Loaded Single-Stage Axial-Flow Low-Speed Compressor
Authors: Friedrichs Jens , Baumgarten Sven , Kosyna Gu¨nter , Stark Udo
Published: July 2002

The paper describes an experimental investigation of the stator hub and blade flow in two different stators of a highly loaded single-stage axial-flow low-speed compressor. The first stator (A) is a conventional design with blades of rectangular planform. The second stator (K) is an unconventional, more advanced design with blades of a special planform, characterized by an aft-swept leading edge with increasing sweep angle toward hub and casing. The experimental results show that stator K exhibits a much better hub performance than stator A, finally leading to a better overall performance of stage K compared to stage A. The better hub performance of stator K is, primarily, the result of a planform effect of the newly introduced blades with an aft-swept leading edge and the aerodynamics of an aft-swept wing.
Local Heat Transfer Distributions in Confined Multiple Air Jet Impingement
Authors: Garimella Suresh V. , Schroeder Vincent P.
Published: July 2002

Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000<Re<20,000), orifice-to-target spacing 0.5<H/d<4, and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Predictive correlations are proposed for single and multiple jet impingement heat transfer.
Reliable Rotor Dynamic Design of High-Pressure Compressors Based on Test Rig Data1
Authors: Wagner N. G.
Published: July 2002

The overall design of high-pressure centrifugal compressors is largely influenced by rotordynamic aspects. Rotor instability may restrict operating speed and/or maximum discharge pressure if the destabilizing effects have not been considered accurately during the design phase. A test rig for high pressures has been designed and operated successfully in order to achieve dynamic labyrinth seal coefficients through simulation of original conditions in every aspect. Details are given of the full-scale test rig, which uses active magnetic bearings as a key feature, as well as results from the comprehensive test program. Later on, these results are employed for the design of a compressor for very high pressures, demonstrating the complexity of this design task. Validation of the labyrinth test data and the rotor dynamic analysis is provided by the results from a PTC 10 class I test on a reinjection compressor. During shop testing, this machine has been run with and without swirl brakes and the test results agree very well with the predictions.
Optimal Design of Rotor-Bearing Systems Using Immune-Genetic Algorithm
Authors: Choi Byeong-Keun , Yang Bo-Suk
Published: July 2002

In this paper, the new combined algorithm (Immune-Genetic Algorithm, IGA) is applied to minimize the total weight of the shaft and the resonance response (Q factor), and to yield the critical speeds as far from the operating speed as possible. These factors play very important roles in designing a rotor-bearing system under the dynamic behavior constraints. The shaft diameter, the bearing length and clearance are chosen as the design variables. The results show that the IGA can reduce the weight of the shaft and improve the critical speed and Q factor with dynamic constraints.
Influence of Material Properties and Forming Velocity on the Interfacial Slip Characteristics of Cross Wedge Rolling
Authors: Deng Zhi , Lovell Michael R. , Tagavi Kaveh A.
Published: July 2002

By means of the explicit dynamic finite element method, the relationship between the tool-workpiece interfacial slip and several cross wedge rolling (CWR) variables is investigated for a flat-wedge CWR process. After defining the components of interfacial slip and area reduction, an experimentally validated finite element model of CWR is introduced. This model is used to analyze a total of 189 distinct operating conditions by varying workpiece material (aluminum 1100, steel 1018 and brass C21000), forming velocity 0.4∼4.0 m/s, area reduction (25 percent, 40 percent and 55 percent) and forming angle (20 deg, 30 deg and 40 deg). The numerical results indicated that forming velocity was an important variable in determining the interfacial slip characteristics of the CWR process analyzed. Additionally, the area reduction and forming angle were found to have a significant influence on the interfacial slip under the conditions considered.
Cryosurgery of Normal and Tumor Tissue in the Dorsal Skin Flap Chamber: Part II—Injury Response
Authors: Hoffmann Nathan E. , Bischof John C.
Published: July 2002

It has been hypothesized that vascular injury may be an important mechanism of cryosurgical destruction in addition to direct cellular destruction. In this study, we report correlation of tissue and vascular injury after cryosurgery to the temperature history during cryosurgery in an in vivo microvascular preparation. The dorsal skin flap chamber, implanted in the Copenhagen rat, was chosen as the cryosurgical model. Cryosurgery was performed in the chamber on either normal skin or tumor tissue propagated from an AT-1 Dunning rat prostate tumor, as described in a companion paper (Hoffmann and Bischof, 2001). The vasculature was then viewed at 3 and 7 days after cryoinjury under brightfield and FITC-labeled dextran contrast enhancement to assess the vascular injury. The results showed that there was complete destruction of the vasculature in the center of the lesion and a gradual return to normal patency moving radially outward. Histologic examination showed a band of inflammation near the edge of a large necrotic region at both 3 and 7 days after cryosurgery. The area of vascular injury observed with FITC-labeled dextran quantitatively corresponded to the area of necrosis observed in histologic section, and the size of the lesion for tumor and normal tissue was similar at 3 days post cryosurgery. At 7 days after cryosurgery, the lesion was smaller for both tissues, with the normal tissue lesion being much smaller than the tumor tissue lesion. A comparison of experimental injury data to the thermal model validated in a companion paper (Hoffmann and Bischof, 2001) suggested that the minimum temperature required for causing necrosis was −15.6±4.3°C in tumor tissue and −19.0±4.4°C in normal tissue. The other thermal parameters manifested at the edge of the lesion included a cooling rate of ∼28°C/min, 0 hold time, and a ∼9°C/min thawing rate. The conditions at the edge of the lesion are much less severe than the thermal conditions required for direct cellular destruction of AT-1 cells and tissues in vitro. These results are consistent with the hypothesis that vascular-mediated injury is responsible for the majority of injury at the edge of the frozen region in microvascular perfused tissue.
Surface Fatigue Lives of Case-Carburized Gears With an Improved Surface Finish
Authors: Krantz T. L. , Alanou M. P. , Evans H. P. , Snidle R. W.
Published: July 2002

Previous research provides qualitative evidence that an improved surface finish can increase the surface fatigue lives of gears. To quantify the influence of surface roughness on life, a set of AISI 9310 steel gears was provided with a near-mirror finish by superfinishing. The effects of the superfinishing on the quality of the gear tooth surfaces were determined using data from metrology, profilometry, and interferometric microscope inspections. The superfinishing reduced the roughness average by about a factor of 5. The superfinished gears were subjected to surface fatigue testing at 1.71 GPa (248-ksi) Hertz contact stress, and the data were compared with the NASA Glenn gear fatigue data base. The lives of gears with superfinished teeth were about four times greater compared with the lives of gears with ground teeth but with otherwise similar quality.
Nonlinear Kinematic Hardening Identification for Anisotropic Sheet Metals With Bending-Unbending Tests
Authors: Brunet M. , Morestin F. , Godereaux S.
Published: July 2002

An inverse identification technique is proposed based on bending-unbending experiments on anisotropic sheet-metal strips. The initial anisotropy theory of plasticity is extended to include the concept of combined isotropic and nonlinear kinematic hardening. This theory is adopted to characterize the anisotropic hardening due to loading-unloading which occurs in sheet-metals forming processes. To this end, a specific bending-unbending apparatus has been built to provide experimental moment-curvature curves. The constant bending moment applied over the length of the specimen allows one to determine numerically the strain-stress behavior but without Finite Element Analysis. Four constitutive parameters have been identified by an inverse approach performed simultaneously on the bending and tensile tests. Our identification results show that bending-unbending tests are suitable to model quite accurately the constitutive behavior of sheet metals under complex loading paths.
Serum Lubricant Absorption by UHMWPE Orthopaedic Bearing Implants
Authors: Blanchet Thierry A. , Peterson Scott L. , Rosenberg Kari D.
Published: July 2002

This study investigates fluid absorption behavior of an unirradiated and a heavily crosslinked ultra-high molecular weight polyethylene (UHMWPE) exposed to bovine serum with pressures varying from 0.1 to 10 MPa. The time-response of serum absorption is biphasic, with an initial “soak-in” phase (<1 week) of rapidly increasing mass before settling to a steady-state phase of mass increasing more gradually and linearly with time. Initial soak-in absorption of the unirradiated and crosslinked UHMWPE are very similar, increasing from 0.8 to 4.3 g/m2 as serum pressure is increased from 0.1 to 10 MPa. Steady-state absorption rates of the unirradiated UHMWPE increase from 0.8 to 1.5 (mg/m2)/hr as serum pressure is increased from 0.1 to 10 MPa, while absorption rates for the crosslinked UHMWPE are lower, increasing from approximately 0.28 to 0.85 (mg/m2)/hr over the same pressure range. Steady-state rate of absorption is also found to depend on temperature, with values at room temperature being two-fold less than at 37°C. Such fluid absorption characterization is critical to hip and knee simulator testing, in order to separate wear loss and serum absorption gain contributions to total mass change measurements of UHMWPE bearings. In addition to its pertinence in quantification of UHMWPE wear, the extent of fluid film lubrication in total joint replacements as implied by reported serum absorption behavior is also discussed.