bluuebunny/crossref_metadata_2025 huggingface dataset:
Robot positioning and the global navigation satellite system
Authors: Ashkenazi Vidal , Park David , Dumville Mark
Published: July 2002

Presents an overview of how satellite‐based positioning techniques could be used to develop novel navigational methods for use on mobile robotic platforms. Details are given of the major terrestrial techniques, both internal and external to the robot, which have been traditionally used to meet positioning requirements. A descriptive summary of the global positioning system of navigation satellites (GPS) is followed by an introduction to Galileo, the European project on the development of a comparable system. A small number of examples, either near to market or in use now, are used to illustrate the use of robotic systems that use GPS as a source of 3D absolute position information, but also velocity, attitude and time. Concludes that GPS is likely to become the universal positioning standard for outdoor applications, with future augmentations and developments enhancing the reliability, integrity and accuracy of the system. Nevertheless, in most cases it will still be necessary to use GPS in combination with alternative positioning sensors.
Features 3D scanning systems for rapid prototyping
Authors: Clark Jim
Published: July 2002

Discusses the use of two commercially available non‐contact laser triangulation sensors. First, describes a standard dual view sensor called REVERSA and demonstrates the use of the scanner in the production of flatware tooling. Second, introduces a novel hand‐held scanner which is retro‐fitted to a portable CMM and describes two examples of its use in the automotive industry.
Properties of precipitated silicas, modified with 3‐amino‐propyltriethoxysilane as semi‐finished product for preparation of pigments
Authors: Krysztafkiewicz Andrzej , Binkowski Slawomir
Published: July 2002

Surface of precipitated silica was modified with 3‐aminopropyltriethoxysilane. The optimum solvent was selected, in which the silane coupling agent was deposited on silica surface. Basic physicochemical properties of the modified silica were estimated. Methods of evaluating silica surface modification extent were presented, taking advantage first of all of its altered hydrophilicity and of differences in condensation extent of surface silanol groups. The modified silica was used as adsorbent capable of trapping water soluble organic amines.
Budgetary response attitudes in a university environment
Authors: Goodwin David R. , de Gouw Bart
Published: July 2002

Hypothesizes that, for academics, while budgetary communication may be positively related to budgetary attitudinal response, this relationship is dependent on the level of influence allowed over the medium/long term goal set. For university administrators, it is not expected that the interaction between the level of influence and budgetary communication will be significant. These differing outcomes are expected because of the conflicting objectives that exist between the two groups. Tests the hypotheses by surveying academic heads of department and administrators from New Zealand universities. The results support the theorized expectations. Outlines the implications for university management and in particular the potential impact for planning structures.
Foreign direct investment in Bulgaria: patterns and prospects
Authors: Glaister Keith W. , Atanasova Hristina
Published: July 2002

This article examines the nature and role of foreign direct investment in Bulgaria. Set in the context of the transitional economies of the countries of Central and Eastern Europe, the article serves to illustrate the importance of foreign direct investment in bolstering the market system, rebuilding the economy and underpinning the success of the privatisation process. An account of the pattern of foreign direct investment in terms of time period, sector and nationality of the investor is presented from official data sources. Since the collapse of communism the Bulgarian economic and political climate has been one of the least conducive in Central and Eastern Europe to the attraction of foreign businesses; however, recent reforms, and in particular the election of a new government, provide the beginning of a more favourable environment for foreign direct investment in Bulgaria.
Natural convection in an inclined enclosure
Authors: Rasoul J. , Prinos P.
Published: July 2002

The effect of inclination on laminar natural convection in a square cavity is studied numerically for inclination angles ranging from 40° to 160°, Rayleigh numbers between 103 and 106 and Prandtl numbers from 0.02 to 4,000. Contours of stream functions and temperature are presented in order to provide a new insight and a better understanding of the flow and heat transfer characteristics in a square cavity. Finds computed local and mean Nusselt numbers at the hot wall in satisfactory agreement with experimental and other numerical results. Finds the mean heat flux at the hot wall as well as the distribution of the local heat flux along the heated wall are found to depend on the inclination angle, the Rayleigh number and the Prandtl number. Such a dependence is significant for angles greater than 90°, while for smaller angles the effect of the inclination angle on the Nusselt‐Rayleigh correlation is weaker.
What is the function of a university? Ivory tower or trade school for plumbers?
Authors: Barrett Brenda
Published: July 2002

In 1967 an academic wrote: “AA university is not a trade school for the production of plumbers”. He wrote about legal education which in England, as in many other countries, has a tradition of recognising academic study and vocational training as separate stages on the route to professional qualification. Thirty years ago universities catered for a relatively small sector of the population; concentrating on undergraduate studies for students entering at the age of 18. Notes the evolution in universities since that time and debates the experience universities should be providing for students today. It will suggest that the failure to distinguish the various forms of higher education is detrimental to the degree and this in turn is harmful to universities. It will conclude by questioning whether Dearing is likely to provide appropriate solutions to the problems
Legal snarls for women in cyberspace
Authors: Kramarae Cheris , Kramer Jana
Published: July 2002

Many Internet researchers state that computer networks provide an
egalitarian forum where users are not labeled by gender, race, age,
national origin or disability. This assertion ignores the experiences of
many women using electronic communication systems. Focusses on several
legal issues of special relevance to women, including pornography and
hate speech, stalking and sexual harassment, and exclusionary practices.
Suggests that the conceptual models used in this research and Internet
work may help to determine future legal practices.
Benchmarking in local government under a central government agenda
Authors: Ball Amanda , Bowerman Mary , Hawksworth Shirley
Published: July 2002

Examines the practical experience of benchmarking in the UK local government sector during the period leading to the introduction of an important policy initiative for local government under “New Labour”. Argues that, under conditions of fiscal control, benchmarking has been subsumed under the wider practice of performance measurement in the sector. A critical factor is the primacy of the role of performance monitoring in local government, which in turn results from the controlling nature (in fiscal and political terms) of UK central government. The corollary is a conflation of two distinct views of benchmarking: benchmarking as a rigorous and challenging scrutiny of local government processes; and benchmarking as an instrument of central government control. Such a state of affairs would appear to offer a number of advantages to those policy makers whose blueprint for the reform of local government encourages the use of benchmarking across the sector.
Crystal structure of threonine synthase from Arabidopsis thaliana
Authors: Thomazeau Karine , Curien Gilles , Dumas Renaud , Biou Valérie
Published: July 2002

Threonine synthase (TS) is a PLP‐dependent enzyme that catalyzes the last reaction in the synthesis of threonine from aspartate. In plants, the methionine pathway shares the same substrate, O‐phospho‐L‐homoserine (OPH), and TS is activated by S‐adenosyl‐methionine (SAM), a downstream product of methionine synthesis. This positive allosteric effect triggered by the product of another pathway is specific to plants. The crystal structure of Arabidopsis thaliana apo threonine synthase was solved at 2.25 Å resolution from triclinic crystals using MAD data from the selenomethionated protein. The structure reveals a four‐domain dimer with a two‐stranded β‐sheet arm protruding from one monomer onto the other. This domain swap could form a lever through which the allosteric effect is transmitted. The N‐terminal domain (domain 1) has a unique fold and is partially disordered, whereas the structural core (domains 2 and 3) shares the functional domain of PLP enzymes of the same family. It also has similarities with SAM‐dependent methyltransferases. Structure comparisons allowed us to propose potential sites for pyridoxal‐phosphate and SAM binding on TS; they are close to regions that are disordered in the absence of these molecules.
Nested allosteric interactions in the cytoplasmic chaperonin containing TCP‐1
Authors: Kafri Galit , Willison Keith R. , Horovitz Amnon
Published: July 2002

Initial rates of ATP hydrolysis by the chaperonin containing TCP‐1 (CCT) from bovine testis were measured as a function of ATP concentration. Two allosteric transitions are observed: one at relatively low concentrations of ATP (<100 μM) and the second at higher concentrations of ATP. The data suggest that CCT has positive intra‐ring cooperativity and negative inter‐ring cooperativity in ATP hydrolysis, with respect to ATP, as previously observed in the case of GroEL. It is shown that the relatively weak positive intra‐ring cooperativity found in the case of CCT may be due to heterogeneity in its subunit composition. Our results suggest that nested allosteric behavior may be common to chaperone double‐ring systems.
Sodium channel function and the excitability of human cutaneous afferents during ischaemia
Authors: Lin Cindy S.‐Y. , Grosskreutz Julian , Burke David
Published: July 2002

The changes in excitability of cutaneous afferents in the median nerve of healthy subjects were compared during 13 min of ischaemia and during 13 min continuous depolarizing DC. In addition, intermittent polarizing currents were used to compensate for or to accentuate the threshold change produced by ischaemia. Measurements were made alternately of the ischaemic (or current‐induced) changes in threshold, refractoriness and, in some experiments, supernormality. The strength‐duration time constant (τSD) was calculated from the thresholds to test stimuli of different duration. During ischaemia for 13 min, the threshold decreased steadily by 34 % over the initial 8 min, reached a plateau and increased slightly over the final few minutes. However, with continuous depolarizing DC, the threshold decreased linearly with the applied current, by 55 % with strong current ramps. Intermittent injection of hyperpolarizing DC was used to compensate for the ischaemic threshold change, but the compensating current increased progressively and did not reach a plateau as had occurred with the ischaemic threshold change. During ischaemia, τSD increased to a plateau, following the threshold more closely than the current required to compensate for threshold. Refractoriness, on the other hand, increased more steeply than the applied compensating current. There were similar discrepancies in the relationships of τSD and refractoriness to supernormality. The smaller‐than‐expected threshold change during ischaemia could result from limitations on the change in excitability produced by ischaemic metabolites acting on the gating and/or permeability of Na+ channels. Intermittent depolarizing DC was applied during the ischaemic depolarization to determine whether it would reduce or accentuate the discrepancies noted during ischaemia alone. The extent of the threshold change was greater than with ischaemia alone, and there was a greater change in τSD and a proportionately smaller change in refractoriness. It is concluded that ischaemia produces factors that can block Na+ channels and/or alter their gating. Without these processes, the ischaemic change in threshold would be much greater than that actually recorded, probably sufficient to produce prominent ectopic impulse activity.
Characterization of basolateral K+ channels underlying anion secretion in the human airway cell line Calu‐3
Authors: Cowley Elizabeth A. , Linsdell Paul
Published: July 2002

Transepithelial anion secretion in many tissues depends upon the activity of basolateral channels. Using monolayers of the Calu‐3 cell line, a human submucosal serous cell model mounted in an Ussing chamber apparatus, we investigated the nature of the K+ channels involved in basal, cAMP‐ and Ca2+‐stimulated anion secretion, as reflected by the transepithelial short circuit current (Isc). The non‐specific K+ channel inhibitor Ba2+ inhibited the basal Isc by either 77 or 16 % when applied directly to the basolateral or apical membranes, respectively, indicating that a basolateral K+ conductance is required for maintenance of basal anion secretion. Using the K+ channel blockers clofilium and clotrimazole, we found basal Isc to be sensitive to clofilium, with a small clotrimazole‐sensitive component. By stimulating the cAMP and Ca2+ pathways, we determined that cAMP‐stimulated anion secretion was almost entirely abolished by clofilium, but insensitive to clotrimazole. In contrast, the Ca2+‐stimulated response was sensitive to both clofilium and clotrimazole. Thus, pharmacologically distinct basolateral K+ channels are differentially involved in the control of anion secretion under different conditions. Isolation of the basolateral K+ conductance in permeabilized monolayers revealed a small basal and forskolin‐stimulated Isc. Finally, using the reverse transcriptase‐polymerase chain reaction, we found that Calu‐3 cells express the K+ channel genes KCNN4 and KCNQ1 and the subunits KCNE2 and KCNE3. We conclude that while KCNN4 contributes to Ca2+‐activated anion secretion by Calu‐3 cells, basal and cAMP‐activated secretion are more critically dependent on other K+ channel types, possibly involving one or more class of KCNQ1‐containing channel complexes.
Effects of prevailing hypoxaemia, acidaemia or hypoglycaemia upon the cardiovascular, endocrine and metabolic responses to acute hypoxaemia in the ovine fetus
Authors: Gardner D. S. , Fletcher A. J. W. , Bloomfield M. R. , Fowden A. L. , Giussani D. A.
Published: July 2002

Although it is established that the fetus can successfully withstand a single, acute hypoxaemic challenge during gestation, little is known about what effects prevailing adverse intrauterine conditions might have on the fetal response to acute hypoxaemia. The aims of this study were therefore: (1) to characterise the effects of prevailing and sustained hypoxaemia, acidaemia or hypoglycaemia on the fetal cardiovascular responses to an episode of acute hypoxaemia; and (2) to determine the effects of these adverse intrauterine conditions on mechanisms mediating these cardiovascular responses. Thirty‐three Welsh Mountain sheep fetuses were chronically instrumented (1–2 % halothane) between 117 and 125 days of gestation (term is ca 145 days) with amniotic and vascular catheters and with a transit‐time flow probe around a femoral artery. The animals were divided retrospectively into four groups based upon post‐surgical, sustained, basal blood oxygen (chronically hypoxaemic; Pa,O2, 17.3 ± 0.5 mmHg; n= 8), glucose (chronically hypoglycaemic; blood glucose, 0.49 ± 0.03 mmol l−1; n= 6) and acid‐base (chronically acidaemic; pHa, 7.25 ± 0.01; n= 5) status. Values for compromised fetuses were −2 s.d. from a group of control (n= 14) fetuses. At 130 ± 4 days, a 1 h episode of acute, isocapnic hypoxaemia (9 % O2 in N2, to reduce carotid Pa,O2 to 12 ± 1 mmHg) was induced in all fetuses by reducing the maternal inspired O2 fraction (FI,O2). Fetal cardiovascular variables were recorded at 1 s intervals throughout the experimental protocol and arterial blood samples taken at appropriate intervals for biophysical (blood gases, glucose, lactate) and endocrine (catecholamines, vasopressin, cortisol, ACTH) measures. During acute hypoxaemia all fetuses elicited hypertension, bradycardia and femoral vasoconstriction. However, prevailing fetal compromise altered the cardiovascular and endocrine responses to a further episode of acute hypoxaemia, including: (1) enhanced pressor and femoral vasoconstriction; (2) greater increments in plasma noradrenaline and vasopressin during hypoxaemia; and (3) basal upward resetting of hypothalamic‐pituitary‐adrenal axis function. Only chronically hypoxaemic fetuses had significantly elevated basal concentrations of noradrenaline and enhanced chemoreflex function during acute hypoxaemia. These data show that prevailing adverse intrauterine conditions alter the capacity of the fetus to respond to a subsequent episode of acute hypoxaemia; however, the partial contributions of hypoxaemia, acidaemia or hypoglycaemia to mediating these responses can vary.
Fusion Zone Shapes in Electron-Beam Welding Dissimilar Metals
Authors: Wei P. S. , Kuo Y. K. , Ku J. S.
Published: July 2002

Experiments on welding dissimilar metals, such as aluminum or copper to iron with an electron-beam welder, are conducted. It is found that the observed depth-to-width ratio of the fusion zone in aluminum can be greater than unity while that in iron is around unity. The former is attributed to the formation of a cavity resulting from a high vapor pressure. The difference in depths increases with beam power. The observed depth-to-width ratios of fusion zones in welding copper to iron can be greater than unity. A unique maximum depth is near the joint plane, as a result of strong convective mixing and high incident flux, even though the melting temperatures are different. Strong mixing is confirmed by measured concentration profiles across the fusion zones of dissimilar metals. To a first approximation fusion zone depths with depth-to-width ratios greater than or identical to unity are determined from scale analyses of heat conduction equations in welding the same metals with a high and low-power-density beam, respectively. The propositions are verified by experimental results. [S0022-1481(00)00103-1]
Natural Convection Heat Transfer and Entropy Generation From a Horizontal Cylinder With Baffles
Authors: Abu-Hijleh B. A/K
Published: July 2002

The problem of laminar natural convection heat transfer from a horizontal cylinder with multiple, equally spaced, low conductivity baffles on its outer surface was investigated numerically. The effect of several combinations of number of baffles and baffle height on the average Nusselt number was studied over a wide range of Rayleigh numbers. The computed velocity and temperature fields were also used to calculate the local and global entropy generation for different cylinder diameters. The results showed that there was an optimal combination of a number of baffles and baffle height for minimum Nusselt number for a given value of the Rayleigh number. Short baffles slightly increased the Nusselt number at small values of the Rayleigh number. The global entropy generation increased monotonically with increasing Rayleigh number and decreased with increasing cylinder diameter, baffle height, and number of baffles. [S0022-1481(00)01203-2]
Simultaneous Optimization of Machining Parameters for Dimensional Instability Control in Aero Gas Turbine Components Made of Inconel 718 Alloy
Authors: Subhas B. K. , Bhat Ramaraja , Ramachandra K. , Balakrishna H. K.
Published: July 2002

Aero gas turbine components made of Inconel 718 superalloy revealed significant dimensional instability after machining. The dimensional instability is a manifestation of alterations in residual stresses and microstructure, which are influenced by machining parameters. This paper presents a simultaneous optimization technique used to control the dimensional instability in turning operation. Empirical equations are established for predicting surface residual stresses, surface finish, dimensional instability and tool life using response surface methodology. Experimental results show a strong correlation between residual stresses and dimensional instability. A desirability function approach is used to optimize the multiple responses and machining parameters are derived for practical applications. Inconel 718 test specimen and jet engine components machined with optimal cutting parameters show dimensional instability within the acceptable tolerance band. [S1087-1357(00)01704-4]
Comparison of Mechanical Properties of Various Suture Repair Techniques in a Partially Lacerated Tendon
Authors: Zobitz Mark E. , Zhao Chunfeng , Amadio Peter C. , An Kai-Nan
Published: July 2002

The technique of surgical repair for zone two flexor tendon injuries has been debated extensively throughout the years, yet adhesion formation, suture rupture, and suture locking on the pulley edge remain possible consequences of a poor repair. The partially lacerated tendon is especially challenging to treat since there can be justification for not intervening surgically. In a partial laceration canine model we measured failure load and suture gap formation for tendons repaired with the Lee, modified four-strand Savage, Kessler, modified Kessler, and Augmented Becker core suture techniques and with a simple running peripheral suture. The modified Kessler (106.3 N, SD 18.8 N) and modified Savage (108.2 N, SD 19.9 N) repair techniques had a significantly higher failure load than the Lee (85.0 N, SD 20.6 N) suture method p<0.05, while there were no differences among the other techniques. There were no significant differences in resistance to gap formation among the repair techniques, with the mean values ranging from 38.9 N/mm (SD 15.7 N/mm) using the simple running suture to 53.2 N/mm (SD 25.8 N/mm) with the Kessler repair. The mean load to produce a 1.5 mm repair site gap ranged from 71.1 N (SD 21.5 N) in the Lee repair to 91.3 N (SD 22.2 N) in the Augmented Becker repair although there were no significant differences among repair methods. All repair methods were much weaker than tendons left unrepaired (184.7 N, SD 41.3 N). [S0148-0731(00)00706-8]
External Longitudinal Flaws in Pipes Under Complex Loading
Authors: Brighenti Roberto
Published: July 2002

A round pipe with an external longitudinal surface flaw is assumed to be subjected to different types of elementary hoop stress distributions acting perpendicular to the crack faces. The stress intensity factors (SIFs) along the crack front for such elementary cases are determined through the three-dimensional finite element method. Then these results are used to compute approximate values of SIFs in the case of complex loadings (such as internal pressure, thermal stresses, residual stresses due to plasticization, etc.), by employing both the superposition principle and the power series expansions of the actual hoop stresses. Thick and thin-walled pipes are examined, and some results are compared with those presented by other authors.
Gap Formation and Interfacial Heat Transfer Between Thermoelastic Bodies in Imperfect Contact
Authors: Lee S. L. , Ou C. R.
Published: July 2002

In this paper, the integration scheme is employed to solve a coupling problem of transient heat conduction and displacement due to thermal deformation. Based on the resulting displacement, gap or contact pressure on the interface of two thermoelastic bodies in imperfect contact is estimated. Such information is then used to determine the interfacial heat transfer between the two thermoelastic bodies. This again affects the temperature distribution and thus the thermal deformation. In the course of heat transfer and thermal deformation, effect of thermal rectification also is taken into account. Numerical solutions of transient and steady-state quantities including gap formation, normal stress, and temperature are demonstrated for a pair of stainless steel and aluminum with conforming shapes. Such an analysis of conduction-deformation interaction based on a finite-difference-like scheme has not been studied in the past.
Flow Characteristics Inside Circular Injection Holes Normally Oriented to a Crossflow: Part I — Flow Visualizations and Flow Data in the Symmetry Plane
Authors: Lee Sang Woo , Park Sang Won , Lee Joon Sik
Published: July 2002

Experimental results are presented that describe flow behavior inside circular injection holes with a sharp square-edged inlet. Oil-film flow visualizations and mean flow data are obtained in the flow symmetry plane of injection holes that are normally oriented to a crossflow. Additional visualizations inside inclined holes are also performed for inclination angles of 30 and 60 deg. Data are presented for three different length-to-diameter ratios: L/D=0.5, 1.0, and 2.0. The blowing ratio is fixed at M=2.0 in the flow visualizations and takes the values M=0.5, 1.0, and 2.0 in the flow measurements. The normal-injection flow visualization in the case of L/D=2.0 clearly demonstrates the existence of four distinct near-wall flow regions: an inlet separation region, a reattachment region, a developing region, and a near-exit flow region. When L/D=1.0 and 2.0, an inlet separation bubble is apparent with a clear imprint of recirculating flow traces, especially on the windward side, even though it is not so well organized on the opposite side. For a short hole such as L/D=0.5, however, the separation bubble with flow recirculation seems to be suppressed by the crossflow. Due to the presence of the inlet separation bubble, actual flow passage is in the form of a converging–diverging channel, regardless of the L/D values. In general, the crossflow stabilizes the inside flow on the leeward side, meanwhile destabilizes it on the windward side. On the contrary, the inclination of the injection hole in the leeward direction of the crossflow stabilizes the flow near the windward wall but destabilizes it near the leeward wall. Relatively short holes such as L/D=0.5 and 1.0 do not allow the boundary-layer development on the wall. Particularly in the case of L/D=0.5, a direct interference is observed between the complicated inlet and exit flows. The inlet flow, however, seems to be isolated from the exit flow for a long hole such as L/D=2.0. It is also found that the potential-core inside the normal injection hole comprises a converging flow region, a diverging flow region, a developing flow region, and a flow region deflected by the crossflow.
Thermoelastic Behavior of Filled Molding Compounds: Composite Mechanics Approach
Authors: Uschitsky M. , Suhir E. , Kammlott G. W.
Published: July 2002

Reliability of epoxy molding compounds used in plastic packages of integrated circuit (IC) devices depends to a great extent on the level of thermal stresses. These are due primarily to the thermal expansion (contraction) mismatch of the epoxy and the silicon materials. In this analysis we assess the effect of silica fillers on the level of thermal stresses. We conclude that thermal stresses in the compound can indeed be reduced by the application of appropriate fillers. We found that the filler volume concentration does not have to be larger than 30 percent to keep the thermal stresses at a sufficiently low level. This number is close to the filler volume concentration of 30–40 percent in commercially available molding compounds. The obtained results and recommendations can be helpful in the analysis of stresses in, and physical design of, plastic packages.
Treatment of 2,4-Dichlorophenol by Solar Photocatalysis: Comparison of Coupled Photocatalytic-Active Carbon vs. Active Carbon
Authors: Malato Sixto , Blanco Julia´n , Ferna´ndez-Iba´n˜ez Pilar , Ca´ceres Julia
Published: July 2002

The photocatalytic oxidation of 2,4-Dichlorophenol (DCP), using TiO2 suspensions under solar radiation, has been studied at pilot-plant scale at the Plataforma Solar de Almerı´a (PSA). This compound is used as a model to demonstrate the practical application of the treatment. Total Organic Carbon (TOC) analysis is applied to confirm the total mineralization of the contaminants. The pilot plant has a volume of 247 L and consists of 9 m2 of CPC modules (with transparent tubes) connected to a recirculation tank. DCP at 20, 50 and 200 mg/L is completely photodegraded in the presence of 200 mg/L of TiO2, but mineralization is slow when organics concentration is small. The results obtained from these experiments have been used to decide the dimensions of a solar photocatalytic plant for treating wastewater contaminated with different concentration of DCP. Due to the slow kinetic obtained in the photodegradation last steps, a combination with GAC treatment is proposed. Besides, this article attempts to compare the advantages, disadvantages and costs of photocatalytic treatment, versus other more conventional technologies such as active carbon adsorption.
Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions
Authors: Karamanis N. , Martinez-Botas R. F. , Su C. C.
Published: July 2002

The performance and detailed flow characteristics of a high pressure ratio mixed flow turbine has been investigated under steady and pulsating flow conditions. The rotor has been designed to have a nominal constant incidence (based on free vortex flow in the volute) and it is for use in an automotive high speed diesel turbocharger. The results indicated a departure from the quasi-steady analysis commonly used in turbocharger turbine design. The pulsations from the engine have been followed through the inlet pipe and around the volute; the pulse has been shown to propagate close to the speed of sound and not according to the bulk flow velocity as stated by some researchers. The flow entering and exiting the blades has been quantified by a laser Doppler velocimetry system. The measurements were performed at a plane 3.0 mm ahead of the rotor leading edge and 9.5 mm behind the rotor trailing edge. The turbine test conditions corresponded to the peak efficiency point at 29,400 and 41,300 rpm. The results were resolved in a blade-to-blade sense to examine in greater detail the nature of the flow at turbocharger representative conditions. A correlation between the combined effects of incidence and exit flow angle with the isentropic efficiency has been shown. The unsteady flow characteristics have been investigated at two flow pulse frequencies, corresponding to internal combustion engine speeds of 1600 and 2400 rpm. Four measurement planes have been investigated: one in the pipe feeding the volute, two in the volute (40 deg and 130 deg downstream of the tongue) and one at the exit of the turbine. The pulse propagation at these planes has been investigated; the effect of the different planes on the evaluation of the unsteady isentropic efficiency is shown to be significant. Overall, the unsteady performance efficiency results indicated a significant departure from the corresponding steady performance, in accordance with the inlet and exit flow measurements.
Experimental and Numerical Investigation on the Evaporation of Shear-Driven Multicomponent Liquid Wall Films
Authors: Gerendas M. , Wittig S.
Published: July 2002

The presented work is concerned with two-phase flows similar to those in prefilming airblast atomizers and combustors employing film vaporization. Correlations for the multicomponent mixture properties and models for the calculations of the multicomponent evaporation were implemented in a well tested elliptic finite-volume code GAP-2D (S. Wittig et al., 1992, “Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gas,” ASME J. Eng. Gas Turbines Power 114, pp. 395–400) utilizing time-averaged quantities, k,ε turbulence model, wall functions, and curve-linear coordinates in the gas phase, adiabatic or diabatic conditions at the film plate, partially turbulent velocity profile, uniform temperature, and a rapid mixing approach in the wavy film. This new code GAP-2K was tested for stability, precision, and grid independence of the results by applying it to a turbulent hot air flow over a two-component liquid film, a mixture of water and ethanol in different concentrations. Both simulations and experiments were carried out over a wide range of inlet conditions, such as inlet pressure (1–2.6 bar), inlet temperature (298–573 K), inlet air velocity (30–120 m/s), initial liquid flow rate (0.3–1.2 cm2/s), and initial ethanol concentration (20–75 percent mass). Profiles of temperature, gas velocity, and concentration of the evaporating component normal to the film, and the development of the film temperature, the static pressure, the liquid flow rate, and the liquid compound along the film plate have been measured and compared with the simulation, showing a good match.
The Nonlinear Response of Multimode Rotors Supported on Squeeze Film Dampers
Authors: Yakoub R. Y. , El-Shafei A.
Published: July 2002

This paper describes the development of an extremely fast method to obtain the unbalance response of multiple mode rotors supported on squeeze film dampers (SFDs). Planar modal analysis theory is used to model the rotor-SFD system. Undamped critical speed analysis is performed to obtain the rotor eigenvalues and eigenvectors. The SFD nonlinear forces are included in the modal force vector. The system differential equations are constructed and are uncoupled using the orthogonal properties of modal vectors. Assuming circular orbit, consistent with planar modes, the differential equations are converted into algebraic ones. A polynomial in speed is obtained through algebraic manipulations. This polynomial represents the steady-state behavior of the rotor-SFD system. The full unbalance response is directly obtained by finding the roots of the polynomial for each particular orbit. This method is extremely fast compared to numerical integration and to iterative methods. The developed method is useful in performing parametric studies and optimum design of SFDs. Twenty-five orders of magnitude computer time savings are reported. Parametric studies of an aircraft gas turbine fan rotor supported by an SFD are presented. The parametric studies show the possibility of appropriately locating the SFD, to dampen the rotor modes. In addition, parametric studies are also used to determine the effect of the SFD parameters on the AGTFR unbalance response.
Computation of Flow and Heat Transfer in Two-Pass Channels With 60 deg Ribs
Authors: Jang Yong-Jun , Chen Hamn-Ching , Han Je-Chin
Published: July 2002

Numerical predictions of three-dimensional flow and heat transfer are presented for a two-pass square channel with and without 60 deg angled parallel ribs. Square sectioned ribs were employed along one side surface. The rib height-to-hydraulic diameter ratio e/Dh is 0.125 and the rib pitch-to-height ratio (P/e) is 10. The computation results were compared with the experimental data of Ekkad and Han [1] at a Reynolds number (Re) of 30,000. A multi-block numerical method was used with a chimera domain decomposition technique. The finite analytic method solved the Reynolds-Averaged Navier Stokes equation in conjunction with a near-wall second-order Reynolds stress (second-moment) closure model, and a two-layer k-ε isotropic eddy viscosity model. Comparing the second-moment and two-layer calculations with the experimental data clearly demonstrated that the angled rib turbulators and the 180 deg sharp turn of the channel produced strong non-isotropic turbulence and heat fluxes, which significantly affected the flow fields and heat transfer coefficients. The near-wall second-moment closure model provides an improved heat transfer prediction in comparison with the k-ε model.
Friction Damper Optimization: Simulation of Rainbow Tests
Authors: Sanliturk K. Y. , Ewins D. J. , Elliott R. , Green J. S.
Published: July 2002

Friction dampers have been used to reduce turbine blade vibration levels for a considerable period of time. However, optimal design of these dampers has been quite difficult due both to a lack of adequate theoretical predictions and to difficulties in conducting reliable experiments. One of the difficulties of damper weight optimization via the experimental route has been the inevitable effects of mistuning. Also, conducting separate experiments for different damper weights involves excessive cost. Therefore, current practice in the turbomachinery industry has been to conduct so-called “rainbow tests” where friction dampers with different weights are placed between blades with a predefined configuration. However, it has been observed that some rainbow test results have been difficult to interpret and have been inconclusive for determining the optimum damper weight for a given bladed-disk assembly. A new method of analysis—a combination of the harmonic balance method and structural modification approaches—is presented in this paper for the analysis of structures with friction interfaces and the method is applied to search for qualitative answers about the so-called “rainbow tests” in turbomachinery applications. A simple lumped-parameter model of a bladed-disk model was used and different damper weights were modeled using friction elements with different characteristics. Resonance response levels were obtained for bladed disks with various numbers of blades under various engine-order excitations. It was found that rainbow tests, where friction dampers with different weights are used on the same bladed-disk assembly, can be used to find the optimum damper weight if the mode of vibration concerned has weak blade-to-blade coupling (the case where the disk is almost rigid and blades vibrate almost independently from each other). Otherwise, it is very difficult to draw any reliable conclusion from such expensive experiments.
Experimental and Finite Element Comparison of Various Fixation Designs in Combined Loads
Authors: Shirazi-Adl A. , Patenaude O. , Dammak M. , Zukor D.
Published: July 2002

The short- and long-term successes of tibial cementless implants depend on the initial fixation stability often provided by posts and screws. In this work, a metallic plate was fixed to a polyurethane block with either two bone screws, two smooth-surfaced posts, or two novel smooth-surfaced posts with adjustable inclinations. For this last case, inclinations of 0, 1.5, and 3 deg were considered following insertion. A load of 1031 N was eccentrically applied on the plate at an angle of ∼14 deg, which resulted in a 1000 N axial compressive force and a 250 N shear force. The response was measured under static and repetitive loading up to 4000 cycles at 1 Hz. The measured results demonstrate subsidence under load, lift-off on the unloaded side, and horizontal translation of the plate specially at the loaded side. Fatigue loading increased the displacements, primarily during the first 100 cycles. Comparison of various fixation systems indicated that the plate with screw fixation was the stiffest with the least subsidence and liftoff. The increase in post inclination from 0 to 3 deg stiffened the plate by diminishing the liftoff. All fixation systems demonstrated deterioration under repetitive loads. In general, the finite element predictions of the experimental fixation systems were in agreement with measurements. The finite element analyses showed that porous coated posts (modeled with nonlinear interface friction with and without coupling) generated slightly less resistance to liftoff than smooth-surfaced posts. In the presence of porous coated posts, Coulomb friction greatly overestimated the rigidity by reducing the liftoff and subsidence to levels even smaller than those predicted for the design with screw fixation. The sequence of combined load application also influenced the predicted response. Finally, the finite element model incorporating measured interface friction and pull-out responses can be used for the analysis of cementless total joint replacement systems during the post-operation period.
Effect of Thermal Property Variation on Surface Grooving
Authors: Teo Kia-Moh , Lafdi Khalid
Published: July 2002

Carbon-carbon composites are used as friction materials because of their exceptional mechanical and thermal properties. In particular, carbon fibers offer high specific stiffness and high thermal diffusivity along the fiber axis. However, it was observed that after being subjected to the braking process, especially after rapid deceleration, the friction surfaces across the rubbing tracks become very wavy. These grooves alter the contact characteristics at the sliding interface and may reduce the friction performance. During the rubbing process, a sliding surface is damaged. In this paper, the effect of thermal property variations on the friction surface is presented. Multiple carbon samples were fabricated with different crystallinity distributions and orientations. All experiments were conducted using a Friction Assessment Screening Tester (FAST) under controlled atmospheric conditions. An experiment using a laser beam to provide the temperature variations across the surface was also performed. The results show that the formation of macro-grooves on the friction surface is a function of thermal or/and mechanical property variations, crystallinity distribution and crystallite orientation with a respect to the rubbing direction. However, if the distribution of crystallites is non-uniform, micro-grooves are always observed.
Investigation of Shallow Water Kinematics and Local Loading Effects on Reliability of Minimum Structures
Authors: Tuty Suhartodjo , Cassidy Mark J. , Ronalds Beverley F.
Published: July 2002

In shallow water, and specifically for minimum structures, the critical wave height exponent α has been shown to vary significantly with structural configuration. Because of the strong relationship to the wave kinematics, α is also sensitive to the wave theory chosen. The North West Shelf offshore Australia has numerous minimum structures located in relatively shallow water, which requires non-linear wave theory. In the near-breaking condition, estimation of the wave crest kinematics is difficult, with Stream Function theory being the most widely used. However, various other wave theories and nonlinear numerical techniques have been developed to predict wave kinematics for shallow water conditions. The following wave theories are compared: regular Stream Function theory, Cnoidal wave theory, Stokes’ theory, NewWave theory, and a second-order correction to NewWave theory. Kinematics, loads and α results are presented for a cylinder in three different water depths.
Mathematical Analysis of Stability and Drift Behavior of Hydraulic Cylinders Driven by a Servovalve
Authors: Richard Edouard , Vivalda Jean C.
Published: July 2002

Hydraulic cylinders are commonly used and many works deal with modeling and control of such devices. This article deals with the stability properties of hydraulic cylinders drift in various situations. The study is based on a classic nonlinear model of these physical systems. The cases of system models without leakages and models with cylinder leakages or servovalve leakages are distinguished and lead to distinct behaviors. The stability properties are proven by various mathematical arguments such as first integrals, Lyapunov theorems, LASALLE invariance principle, BARBALAT’s lemma, and the center manifold theory.
Approximating EHL Film Thickness Profiles Under Transient Conditions
Authors: Messe´ S. , Lubrecht A. A.
Published: July 2002

In ElastoHydrodynamic Lubrication (EHL), transient processes are much more common than stationary ones. Predicting the film thickness under steady state conditions has become straight forward. Using numerical methods, the effect of transient conditions on the film thickness profile can be computed. However, those analyses are very time consuming even using advanced numerical techniques. As such, they are inadequate for industrial applications as design and development. This paper shows that under certain assumptions, an approximate formula of the transient film thickness profile can be derived under transient operating conditions. The variations can occur in the geometry, the load or the hydrodynamic velocity. The theory can handle all variations separately, or even a combination of several parameters varying simultaneously. The analytical approximation obtained is rather good apart from the constriction at the contact edge(s). This approach can be applied to any set of time dependent conditions (load, speed, geometry). As an example an EHL contact is studied in which reversal of the entrainment velocity occurs.
Mobility Analysis of the 3-UPU Parallel Mechanism Assembled for a Pure Translational Motion
Authors: Di Gregorio Raffaele , Parenti-Castelli Vincenzo
Published: July 2002

The occurrence of singular configurations in parallel mechanisms must be avoided during motion since the actuators cannot control motion even in the neighborhood of these configurations. As a consequence, the knowledge of the singular configurations of the mechanism is important for control purposes, for singularity-free path planning, and also represents basic information for the synthesis of a desired mechanism workspace free from singularities. In this paper the mobility analysis of the 3-UPU parallel mechanism assembled for obtaining a pure translation motion of the output platform is performed and both translation and rotation singularity loci are presented in analytic form and their geometric interpretation is given.
Studies of a Heat-Pipe Cooled Piston Crown
Authors: Wang Q. , Cao Y. , Wang R. , Mignano F. , Chen G.
Published: July 2002

Designing pistons with effective cooling is crucial to preventing piston failure and improving engine service life. A piston design that incorporates the heat-pipe cooling technology may provide a new approach that could improve the thermal-tribological performance of heavy-duty diesel engine pistons. A simplified piston crown with an annular reciprocating heat pipe is constructed to demonstrate this concept. The piston crown is experimentally tested on a specially designed reciprocating apparatus. Experimental data indicate that the annular heat-pipe cooling can greatly assist in reducing the temperature gradient and peak temperature along the ring bank. In order to predict the performance in a more realistic piston working condition, a three-dimensional finite element modeling is used to analyze the thermal performance of this annular heat-pipe cooled crown (AHPCC). The heat-transfer coefficient under the reciprocal environment of the experimental apparatus and the effective thermal conductance of the heat pipe are determined by correlating the numerical calculations with the experimental measurements. The results indicate that the heat-pipe-cooling concept presented in this paper can provide an effective means for piston temperature control under real piston operating conditions. [S0742-4795(00)01501-5]