bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Shapes for Axisymmetric Pressure Vessels: A Brief Overview
Authors: Zhu Lei , Boyle J. T.
Published: July 2002

This paper describes how optimal shapes for axisymmetric pressure vessels can be established based on maximizing limit pressure. This type of problem has been rarely examined in the literature due to the difficulty of evaluating limit loads. However, the “elastic compensation method” is used to approximate the limit load using elastic analysis alone, which opens the possibility of studying shape optimization based on limit pressure. The basic procedure, using a commercial finite element analysis system, is described and three example problems are examined. The aim is to investigate how much of an increase in load-carrying capacity could potentially be achieved if nonstandard pressure vessel shapes could be employed in practice. Of course, this may not be possible, but the results described here do contribute to a better understanding of the role shape plays in providing strength to a simple pressure vessel. [S0094-9930(00)00304-8]
Nonlinear Analysis of Pipe Bends Subjected to Out-of-Plane Moment Loading and Internal Pressure
Authors: Mourad Hashem M. , Younan Maher Y. A.
Published: July 2002

The behavior of a pipe bend, with bend factor h=0.1615(D=16 in.,R=24 in. and t=0.41 in.), subjected to out-of-plane bending and internal pressure is studied, taking geometric and material nonlinearity into account, using the finite element code ABAQUS. Material behavior is taken as elastic-perfectly plastic. The distribution of stress and strain along the axial direction and across the thickness of the bend is studied, with and without internal pressure, at the onset of yielding and at instability. Before instability is reached, through-the-thickness yielding appears at many points. The loaded end of the bend is found to be the most severely strained cross section. The circumferential distribution of stress and strain, and its variation with increased moment loading are then investigated for that section, at internal pressure values of zero and 1200 psi.
Some Discussions on the Flow Factor Tensor—Considerations of Roughness Orientation and Flow Rheology
Authors: Li Wang-Long
Published: July 2002

Relations expressing the effects of roughness orientations θi and flow behavior index n of the power-law fluid on the flow factors of area-distributed random roughness in hydrodynamic lubrication are derived. By using a mapping function, the generalized average Reynolds equation contains non-diagonal terms, and the flow factor tensor is symmetrical but not necessarily diagonal according to the coordinate system. Finally, the conditions that two rough surfaces act as though they were perfectly smooth are discussed for some particular combinations. [S0742-4787(00)01604-0]
Numerical Study of the Three-Dimensional Structure of a Bubble Plume
Authors: Murai Y. , Matsumoto Y.
Published: July 2002

The whole behavior and the micro scale flow characteristics of a three-dimensional bubble plume are investigated numerically. The bubble plume drives liquid convection in a tank due to strong local two-phase interaction so that the Eulerian-Lagrangian model is formulated with emphasis on the translational motions of the bubble. In this model, each bubble motion is tracked in a bubbly mixture which is treated as a continuum. The three-dimensional numerical results reveal several particular structures, such as swaying and swirling structures of the bubble plume. These simulated flow structures show qualitatively good agreement with the experimental observations. Furthermore, the detailed behavior in the bubble plume is clarified by various analysis to discuss the dominant factors causing such the strong three-dimensionality. [S0098-2202(00)00904-4]
Assessment of Offshore Platforms Under Subsidence—Part I: Approach
Authors: Gebara Joseph M. , Dolan Dan , Pawsey Stuart , Jeanjean Philippe , Dahl-Stamnes Knut
Published: July 2002

This is the first of four companion papers that present a comprehensive assessment of the effect of sea floor subsidence on the Valhall complex of platforms. The study has included an estimate of the increase in platform failure probability as a function of increased subsidence. Subsidence raises the effective mean still water level and increases the potential for inundation of the deck for extreme storm conditions. Deck wave slam forces generate significantly greater platform loading and lead to: (a) higher levels of structural inelastic response and increased risk of structural failure as well as (b) water reaching the cellar deck, and hence affecting operators as well as equipment. The paper focuses on addressing the first of these two issues. A structural assessment study was performed to address the significance of present and future levels of subsidence on the safety of three North Sea platforms. The study included a systematic assessment procedure that addressed each of the factors that impacted structural integrity issues and reliability concerns. Such factors included: ultimate strength analysis methodologies, tubular joint formulations, group pile effects, and soil-structure interaction, which are described in this paper, as well as deck impact force formulations (Pawsey et al., 1998, “Characterization of Environmental Loads on Subsiding Offshore Platforms,” 17th International Conference on Offshore Mechanics and Arctic Engineering, Lisbon, Portugal, July) component and system reliability modeling (Jha et al., 2000, “Assessment of Offshore Platforms Under Subsidence—Part II: Analysis and Results,” ASME J. Offshore Mech. Arct. Eng., 122, pp. 267–273), and acceptance criteria (Stahl et al., 1998, “Acceptance Criteria for Offshore Platforms,” 17th International Conference on Offshore Mechanics and Arctic Engineering, Lisbon, Portugal, July). This paper presents the assessment procedure, as well as the modeling approach. The paper also discusses the consequence classification of the three platforms and state-of-the-art soil mechanics techniques that lead to a significant increase in the tensile capacity of the foundation. [S0892-7219(00)00204-1]
Assessment of Offshore Platforms Under Subsidence—Part II: Analysis and Results
Authors: Jha Alok K. , Kiciman Omer K. , Gebara Joseph M. , Stahl Bernhard , Dahl-Stamnes Knut H.
Published: July 2002

An assessment of three offshore platforms in the Valhall field of the North Sea is described in this paper. Ultimate strength and reliability analyses were performed for the jacket-type platforms for four levels of sea floor subsidence. The nonlinear structural models of the platform elements, joints, and associated soil-structure interaction are summarized in a companion paper by Gebara et al., 2000, “Assessment of Offshore Platforms Under Subsidence—Part I: Approach,” ASME J. Offshore Mech. Arct. Eng., 122, pp. 260–266. Similarly, environmental loads and reliability acceptance criteria are presented by Pawsey et al., 1998, “Characterization of Environmental Loads on Subsiding Offshore Platforms,” OMAE98, Lisbon, Portugal, and Stahl et al., 1998, “Acceptance Criteria for Offshore Platforms,” OMAE98, Lisbon, Portugal, respectively. This paper describes the procedures employed and results obtained for ultimate strength and reliability analysis. Ultimate platform strength was calculated using a pushover analysis in which environmental loads for increasingly rare events were applied incrementally until the platform failed. Failure was defined as formation of a limiting mechanism in the platform structure or foundation. Structural reliability analysis was performed to estimate the annual probability of platform failure as a function of subsidence level. The platform structural system was modeled in terms of two major subsystems that were assessed as likely to fail: (i) the platform deck, and (ii) the platform jacket and piles. Uncertainties were included in the loads, structural components, and soil strengths based on industry experience and data. First and second-order reliability methods (FORM/SORM) were used to estimate the annual failure probabilities. Consideration was given to the correlated nature of the failure modes due to the common environmental loads. The reliability results were compared with predefined acceptance criteria to judge the suitability of continued operations. [S0892-7219(00)00304-6]
On Symmetrizable Systems of Second Kind
Authors: Adhikari S.
Published: July 2002

We discuss under what conditions multiple-parameter asymmetric linear dynamical systems can be transformed into equivalent symmetric systems by nonsingular linear transformations. So far, in structural dynamics literature this problem has been addressed in the context of the original work by Taussky. Taussky’s approach of symmetrization was based on similarity transformation. In this paper an approach is proposed to transform asymmetric systems into symmetric systems by equivalence transformation. We call Taussky’s approach of symmetrization by similarity transformation “first kind” and proposed approach by equivalence transformation “second kind.” Since equivalence transformations are most general nonsingular linear transformations, conditions of symmetrizability obtained here are more “liberal” than the first kind and numerical calculations also become more straightforward. Several examples are provided to illustrate the new approach. [S0021-8936(00)00504-3]
Visualization and Prediction of Natural Convection of Water Near Its Density Maximum in a Tall Rectangular Enclosure at High Rayleigh Numbers
Authors: Ho C. J. , Tu F. J.
Published: July 2002

An experimental and numerical investigation is presented concerning the natural convection of water near its maximum-density in a differentially heated rectangular enclosure at high Rayleigh numbers, in which an oscillatory convection regime may arise. The water in a tall enclosure of Ay=8 is initially at rest and at a uniform temperature below 4°C and then the temperature of the hot vertical wall is suddenly raised and kept at a uniform temperature above 4°C. The cold vertical wall is maintained at a constant uniform temperature equal to that of the initial temperature of the water. The top and bottom walls are insulated. Using thermally sensitive liquid crystal particles as tracers, flow and temperature fields of a temporally oscillatory convection was documented experimentally for RaW=3.454×105 with the density inversion parameter θm=0.5. The oscillatory convection features a cyclic sequence of onset at the lower quarter-height region, growth, and decay of the upward-drifting secondary vortices within counter-rotating bicellular flows in the enclosure. Two and three-dimensional numerical simulations corresponding to the visualization experiments are undertaken. Comparison of experimental with numerical results reveals that two-dimensional numerical simulation captures the main features of the observed convection flow.
Spray Cooling Under Reduced Gravity Condition
Authors: Yoshida Ken-ichi , Abe Yoshiyuki , Oka Toshiharu , Mori Yasuhiko H. , Nagashima Akira
Published: July 2002

The present paper reports on the results of a series of authors’ parabolic flight experiments on spray cooling in addition to ground-based experiments in which the influence of heater orientation and the behavior of rebounded droplets were especially studied in detail. Water and FC-72 (perfluorocarbon) were employed alternatively as a test liquid sprayed from a single full-cone nozzle onto a Cr-plated surface of an electrically heated copper block for transient cooling experiments or onto a transparent ITO (indium tin oxide) coated surface of a glass block for steady state experiments in a relatively low superheat region. Each experimental run was accomplished within some 15 sec through which a stable reduced gravity condition (0.01 times the terrestrial gravity) was maintained in the aircraft. Cooling curves were obtained over a wide range of each of the following parameters: the wall superheat, the spray volume flux and the Weber number for the spray droplets. It is demonstrated that the gravity dependency of the spray cooling characteristics varies with the spray volume flux and the droplet Weber number. Qualitative interpretations of the observed gravity dependency are provided.
Study of Subcooled Film Boiling on a Horizontal Disc: Part I—Analysis1
Authors: Banerjee D. , Dhir V. K.
Published: July 2002

In this work subcooled film boiling on a horizontal disc was studied analytically/numerically. Linearized stability analysis of a vapor film underlying a pool of heavier liquid was performed in three-dimensional, cylindrical coordinates. From the analysis the dominant wavelength and configuration of vapor releasing nodes was identified. Complete numerical simulation of the nonlinearly evolving interface have been carried out in axisymmetric coordinates. Finite difference method was used to simultaneously solve the equations governing conservation of mass, momentum, and energy in the vapor and liquid phases. The equations for the two phases were coupled through the matching of normal and tangential stresses and continuity of mass and energy at the interface. Second order projection method was employed for decoupling velocities from pressure. Numerical grid generation method was utilized to construct a grid system which was aligned with the interface. From the simulations the shape of the nonlinearly evolving interface, the growth rate of the interface, the flow and temperature fields in the vapor and liquid, and rate of heat transfer from the wall and into the subcooled liquid have been determined.
The Correlation of Simultaneous Heat and Mass Transfer Experimental Data for Aqueous Lithium Bromide Vertical Falling Film Absorption
Authors: Miller William A. , Keyhani Majid
Published: July 2002

A study of simultaneous heat and mass transfer was conducted on a vertical falling film absorber to better understand the mechanisms driving the heat and mass transfer processes. Thermographic phosphors were successfully used to measure the temperature profile along the length of the absorber test tube. These measures of the local variations in temperature enabled calculation of the bulk concentration along the length of the absorber. The bulk concentration varied linearly, which infers that the concentration gradient in the direction of flow is approximately constant. The implication is that the mass flux and therefore the absorber load can be solved for using a constant flux approximation. Design data and correlations are sparse in the open literature. Some experimental data are available; however, all literature data to date have been derived at mass fractions of lithium bromide ranging from 0.30 to 0.60. Experiments were therefore conducted with no heat and mass transfer additive on an internally cooled smooth tube of 0.01905-m outside diameter and of 1.53-m length. The data, for testing at 0.62 and 0.64 mass fraction, were scaled and correlated into both Nu and Sh formulations. The average absolute error in the Nu correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sh correlation is about ±5% of the reduced Sh data. Data from the open literature were reduced to the authors Nu and Sh formulations, and were within 5% of the correlations developed in the present study. The study therefore provides test data with no heat and mass transfer additive and correlations for the coupled heat- and mass-transfer process that are validated against the extensive experimental data.
Role of Solidification, Substrate Temperature and Reynolds Number on Droplet Spreading in Thermal Spray Deposition: Measurements and Modeling
Authors: Wan Y. P. , Zhang H. , Jiang X. Y. , Sampath S. , Prasad V.
Published: July 2002

Numerical analysis and experimental measurements of the flattening degree of plasma sprayed molybdenum and zirconia droplets deposited on different substrate materials are presented. Investigation is focused on the influence of rate of solidification and wetting angle on droplet spreading. Madejski-Zhang model with one-dimensional treatment of solidification as well as heat transfer in the melt, solidified splat and substrate is employed to perform a numerical analysis. A parametric study is conducted to examine the effects of droplet size, impact velocity, superheating of droplets, substrate temperature, thermal contact resistance, and wetting angle on spreading of the splat and its flattening degree. Numerical results show that the time for solidification can be as small as that for spreading and the rate of solidification can greatly influence the flattening degree. A guideline for when the effect of wetting angle and surface tension on droplet deformation can be neglected is derived. A correlation for the relationship between the flattening degree and Reynolds number with the consideration of solidification is deduced, and a criterion for the effect of droplet solidification on impact dynamics to be negligible is given. The limitations of the assumption of isothermal substrate are also discussed. The numerical predictions agree statistically well with the experimental data.
An Elastic-Perfectly Plastic Flow Model for Finite Element Analysis of Perforated Materials
Authors: Jones D. P. , Gordon J. L. , Hutula D. N. , Banas D. , Newman J. B.
Published: July 2002

This paper describes the formulation of an elastic-perfectly plastic flow theory applicable to equivalent solid (EQS) modeling of perforated materials. An equilateral triangular array of circular penetrations is considered. The usual assumptions regarding geometry and loading conditions applicable to the development of elastic constants for EQS modeling of perforated plates are considered to apply here. An elastic-perfectly plastic (EPP) EQS model is developed for a fourth-order collapse surface which is appropriate for plates with a triangular array of circular holes. A complete flow model is formulated using the consistent tangent modulus approach based on the fourth-order function. The EPP-EQS method is used to obtain a limit load solution for a plate subjected to transverse pressure and fixed at the outer edge. This solution is compared to a solution obtained with an EPP-FEA model in which each penetration in the plate is modeled explicitly. The limit load calculated by the EPP-EQS model is 6 percent lower than the limit load calculated by the explicit model.
Mirror Gas Turbines: A Newly Proposed Method of Exhaust Heat Recovery
Authors: Fujii S. , Kaneko K. , Otani K. , Tsujikawa Y.
Published: July 2002

A new conceptual combination of Brayton and inverted Brayton cycles with a heat sink by intercooling, which is dubbed the mirror gas turbine, has been evaluated and proposed in this paper. Prior to such evaluations, a preliminary test on the inverted cycle without intercooling was made experimentally to confirm the actual operation. The conventional method of recuperation in gas turbines can be replaced by the mirror gas turbine with a low working temperature of about 450°C at heat exchanger. The combined cycle of Brayton/Rankine for electricity generation plant may be improved by our concept into a system with steam turbines completely removed and with still high thermal efficiency. Ultra-micro turbines will be possible, producing the output power less than 10 kW as well as thermal efficiency of 20 percent.
A Force-Control Model for Edge-Deburring with Filamentary Brush
Authors: Chen Lienjing , Stango Robert J. , Cariapa Vikram
Published: July 2002

In this paper a force-control model is developed for edge deburring with filamentary brushes. The model is based upon experimentally obtained “master curves,” that is, material removal data that corresponds to the actual machining performance of the brush/workpart system during the incremental burr removal process. This information is used in conjunction with the on-line brush machining force to compute the brush feed rate that ensures complete removal of the edge burr. Computer simulated results are reported for the removal of an edge burr having unknown variable height. The results indicate that the present force-control model can provide a straight forward approach for computing brush feed rates that lead to complete removal of edge burrs, and suggests that implementation can be carried out using a force sensor and a simple control strategy.
Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part I—Experiment
Authors: Storace A. F. , Wisler D. C. , Shin H.-W. , Beacher B. F. , Ehrich F. F. , Spakovszky Z. S. , Martinez-Sanchez M. , Song S. J.
Published: July 2002

An experimental and theoretical investigation has been conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor is displaced from the centerline of the static structure of the engine. This creates circumferentially nonuniform rotor-tip clearances, unsteady flow, and potentially increased clearances if the rotating and stationary parts come in contact. The result not only adversely affects compressor stall margin, pressure rise capability, and efficiency, but also generates an unsteady, destabilizing, aerodynamic force, called the Thomas/Alford force, which contributes significantly to rotor whirl instabilities in turbomachinery. Determining both the direction and magnitude of this force in compressors, relative to those in turbines, is especially important for the design of mechanically stable turbomachinery components. Part I of this two-part paper addresses these issues experimentally and Part II presents analyses from relevant computational models. Our results clearly show that the Thomas/Alford force can promote significant backward rotor whirl over much of the operating range of modern compressors, although some regions of zero and forward whirl were found near the design point. This is the first time that definitive measurements, coupled with compelling analyses, have been reported in the literature to resolve the long-standing disparity in findings concerning the direction and magnitude of whirl-inducing forces important in the design of modern axial-flow compressors.
Period-Doubling Bifurcation and Non-Typical Route to Chaos of a Two-Degree-Of-Freedom Vibro-Impact System
Authors: Wen and G. L. , Xie J. H.
Published: July 2002

A nontypical route to chaos of a two-degree-of-freedom vibro-impact system is investigated. That is, the period-doubling bifurcations, and then the system turns out to the stable quasi-periodic response while the period 4-4 impact motion fails to be stable. Finally, the system converts into chaos through phrase locking of the corresponding four Hopf circles or through a finite number of times of torus-doubling.
Model Transformations to Evaluate Transient Thermal Responses at a Tissue Surface
Authors: Saidel and Gerald M. , Liu Erin H.
Published: July 2002

For a spatially distributed model describing the transient temperature response of a thermistor-tissue system, Wei et al., [J. Biomech. Eng., 117:74–85, 1995] obtained an approximate transformation for fast analysis of the temperature response at the tissue surface. This approximate transformation reduces the model to a single ordinary differential equation. Here, we present an exact transformation that yields a single differential-integral equation. Numerical solutions from the approximate and exact transformations were compared to evaluate the differences with several sets of parameter values. The maximum difference between the exact and approximate solutions did not exceed 15 percent and occurred for only a short time interval. The root-mean-square error of the approximate solution was no more than 5 percent and within the level of experimental noise. Under the experimental conditions used by Wei et al., the approximate transformation is justified for estimating model parameters from transient thermal responses.
A Bounded Region of Disc-Brake Vibration Instability
Authors: Ouyang H. , Mottershead J. E.
Published: July 2002

This paper introduces the velocity-dependent friction law with the Stribeck effect in a moving load model for the vibration and squeal of a car disc brake. Simulated numerical results produce a bounded region of instability for the rotating speed of the disc which is compatible with observed squeal phenomenon.
Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model
Authors: Polifke W. , Flohr P. , Brandt M.
Published: July 2002

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the turbulent flame speed closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e., the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.
Control Optimization of the Transient Performance of the Selective Bleed Variable Cycle Engine During Mode Transition
Authors: Gro¨nstedt U. T. J. , Pilidis P.
Published: July 2002

The transient performance of the selective bleed variable cycle engine (VCE) has been optimized during the transition from subsonic to supersonic mode. The selective bleed VCE concept has been developed with a short take-off vertical landing (STOVL) aircraft in mind and the engine is characterized by its twin mode VCE feature. The transition optimization is constrained by the requirement of maintaining thrust and compressor surge margins. The engine variable geometry component schedules and the fuel flow are used as optimization variables. A differential algebraic formulation of an inter-component volume model is used to model the transient behavior of the engine. Sequential quadratic programming (SQP) is applied to the nonlinear transient engine model directly, in order to solve the multivariable control problem. It is predicted that the mode switch can be carried out safely without violating the constraints and that the time required is limited by the actuator time of the hydraulic system.
Mainstream Aerodynamic Effects Due to Wheelspace Coolant Injection in a High-Pressure Turbine Stage: Part II—Aerodynamic Measurements in the Rotational Frame
Authors: McLean Christopher , Camci Cengiz , Glezer Boris
Published: July 2002

The current paper deals with the aerodynamic measurements in the rotational frame of reference of the Axial Flow Turbine Research Facility (AFTRF) at the Pennsylvania State University. Stationary frame measurements of “Mainstream Aerodynamic Effects Due to Wheelspace Coolant Injection in a High Pressure Turbine Stage” were presented in Part I of this paper. The relative aerodynamic effects associated with rotor–nozzle guide vane (NGV) gap coolant injections were investigated in the rotating frame. Three-dimensional velocity vectors including exit flow angles were measured at the rotor exit. This study quantifies the secondary effects of the coolant injection on the aerodynamic and performance character of the stage main stream flow for root injection, radial cooling, and impingement cooling. Current measurements show that even a small quantity (1 percent) of cooling air can have significant effects on the performance and exit conditions of the high-pressure turbine stage. Parameters such as the total pressure coefficient, wake width, and three-dimensional velocity field show significant local changes. It is clear that the cooling air disturbs the inlet end-wall boundary layer to the rotor and modifies secondary flow development thereby resulting in large changes in turbine exit conditions. Effects are the strongest from the hub to midspan. Negligible effect of the cooling flow can be seen in the tip region.
Nonlinear Excitation Model of Ball Bearing Waviness in a Rigid Rotor Supported by Two or More Ball Bearings Considering Five Degrees of Freedom
Authors: Jang G. H. , Jeong S. W.
Published: July 2002

This research presents a nonlinear model to analyze the ball bearing vibration due to the waviness in a rigid rotor supported by two or more ball bearings. The waviness of a ball and each races is modeled by the superposition of sinusoidal function, and the position vectors of inner and outer groove radius center are defined with respect to the mass center of the rotor in order to consider five degrees of freedom of a general rotor-bearing system. The waviness of a ball bearing is introduced to these position vectors to use the Hertzian contact theory in order to calculate the elastic deflection and nonlinear contact force resulting from the waviness while the rotor has translational and angular motion. They can be determined by solving the nonlinear equations of motion with five degrees of freedom by using the Runge-Kutta-Fehlberg algorithm. Numerical results of this research are validated with those of prior researchers. The proposed model can calculate the translational displacement as well as the angular displacement of the rotor supported by two or more ball bearings with waviness. It also characterizes the vibration frequencies resulting from the various kinds of waviness in rolling elements, the harmonic frequencies resulting from the nonlinear load-deflection characteristics of ball bearing, and the sideband frequencies resulting from nonlinearity of the waviness interaction.
Numerical Modeling of Dynamic Sealing Behaviors of Spiral Groove Gas Face Seals
Authors: Ruan Bo
Published: July 2002

A numerical model is developed for the dynamic analysis of gas lubricated spiral groove face seals. Effects of the rotor runout, misalignment, face contact, as well as the stiffness and damping of the secondary seal are considered. Seal axial and angular motions and key parameters such as torque, power loss, and flow rate are obtained by a global time integration scheme, which traces the time history of the dynamic sealing behaviors. The analysis of gas film lubrication, face contact, and the seal dynamics is cast as an inverse problem and the solution is obtained iteratively at each time step. Dynamic tracking motion and key sealing characteristics of a representative spiral groove gas seal undergoing transient operations are presented.
A Non-Axisymmetric Steady State Model of a Mechanical Seal for Down-Hole Tools
Authors: Xiong Shunhe , Salant Richard F.
Published: July 2002

A non-axisymmetric steady state numerical model has been developed for use in the design of mechanical seals for down-hole tools. It is applicable to other types of mechanical seals in which friction from the static secondary seal is significant, as well. This model predicts such quantities as leakage rate, external fluid incursion rate, film thickness distribution, fluid pressure and contact pressure distributions, interface temperature and face deformation. Model results show that for a given set of operating conditions, there is a range of equilibrium states of the seal, corresponding to a range of inclinations of the non-rotating seal face relative to the rotating face. Depending on the inclination, it is possible to have negative leakage due to the asymmetry of the film thickness distribution. Even with positive leakage, under some circumstances incursion of the external fluid can occur as a result of the asymmetry.
On the Formation of Hot Spots in Wet Clutch Systems
Authors: Jang J. Y. , Khonsari M. M.
Published: July 2002

A comprehensive model is developed for analyzing the onset of thermoelastic instability in a wet clutch. For this purpose, appropriate governing equations are derived that take into account the porosity and deformability of the friction material. The effect of the thickness of the separator disk and that of the friction material are also included. The model is general and can be used to describe TEI in a variety of other systems such as in a mechanical seal, as a special case. A series of simulations are presented that predict the thermoelastic behavior of a wet clutch from an instability viewpoint.
Criterion for Prevention of Central Bursting in Forward Extrusions Through Spherical Dies Using the Finite Element Method
Authors: Sriram S. , Van Tyne C. J.
Published: July 2002

Spherical dies are increasing in popularity in the cold-forming industry because of the ease in subsequent secondary operations. This paper presents criteria curves, calculated using the finite element method, to avoid central bursting or internal chevrons in forward extrusions through spherical dies. Critical values of mean stress at the centerline of the extrusion are used as failure criteria to distinguish between acceptable and unacceptable die designs. These failure criteria are conservative in that the critical step for central bursting is considered to be the formation of a microvoid during extrusion, rather than linking of the voids during continued deformation. The resulting process criteria curves are conservative estimates of internal chevron formation during extrusion through spherical dies.
Oil-Water Two-Phase Flows in Large-Diameter Pipelines
Authors: Shi H. , Cai J. , Jepson W. P.
Published: July 2002

Two-phase oil-water flows in a 10-cm-dia horizontal pipe have been experimentally investigated to study the effect of surfactant on oil-water distributions. Results show that at input water cut of 20 percent and lower, the water layer velocity is lower than mixed layer velocity up to an input mixture velocity of 1.6 m/s. However, at input water cut of 40 percent and higher, the water layer velocity is lower than the mixed layer velocity up to an input mixture velocity of only 0.8 m/s. Oil and water are much easier to be mixed at the medium input water cuts between 40 and 60 percent. The addition of surfactant enhances the degree of mixing of oil-water flow. With an increase of surfactant concentration, the water layer disappears, oil and water start to mix at lower mixture velocity, and the homogeneous flow pattern was observed at much lower input mixture velocity. Also, the mixed layer occupies a much greater fraction of the pipe. These indicate that corrosion could be reduced at lower input superficial mixture velocity with surfactants in oil-water flows.
Performance of a Foil-Magnetic Hybrid Bearing
Authors: Swanson E. E. , Heshmat H. , Walton J.
Published: July 2002

To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated, and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class). This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high-load capacity and high-speed performance of the compliant foil bearing. An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 rpm and the foil bearing component’s ability to function as a backup in case of magnetic bearing failure. At an operating speed of 22,000 rpm, loads exceeding 5300 N were carried by the system. This load sharing could be manipulated by an especially designed electronic control algorithm. In all tests, rotor excursions were small and stable. During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coastdown. The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.
Stress Field in Finite Width Axisymmetric Wound Rolls
Authors: Lee Y. M. , Wickert J. A.
Published: July 2002

A model is developed for predicting the stress field within a wound roll of web material, in which the radial, circumferential, transverse, and shear stresses can vary in both the roll’s radial and cross-web (transverse) directions. As has been the case in previous wound roll stress analyses based on one-dimensional models, the present approach accounts for the anisotropic and nonlinear material properties of the layered web material, and the incremental manner in which the roll is wound. In addition, the present development accounts for arbitrary cross-sectional geometry and material of the core, and the presence of nonuniform tension across the web’s width during winding. The solution is developed through an axisymmetric, two-dimensional, finite element analysis which couples individual models of the core and layered web region substructures. The core’s stiffness matrix at the core-web interface provides a mixed boundary condition for the web region’s first layer. In several parameter studies, variations of the stress components in the roll’s radial and cross-width directions are discussed and compared with predictions of the simpler companion one-dimensional model. The character of the stress field at the web region’s free edges and along the core-web interface, and the possibility of stress concentration or singularity existing there, are also discussed.
Microcontact Model for Paper-Based Wet Friction Materials
Authors: Gao H. , Barber G. C.
Published: July 2002

This paper is focused on the real area of contact for paper-based wet friction materials during the engagement of wet clutches. The deformation of the wet friction material is identified as elastic during the engagement. A microcontact model is proposed considering both surface roughness and skewness. A Weibull density distribution is employed in the model rather than a Gaussian density distribution. This model is compared with the Greenwood-Williamson (GW) model for the cases of positive skewness, zero skewness and negative skewness. The real areas of contact of new, run-in and glazed wet friction materials were investigated using this microcontact model. Both surface roughness and skewness were found to have a great effect on the real area of contact.
Analysis and Design of Robust Motion Controllers in the Unified Framework
Authors: Kim Bong Keun , Choi Hyun-Taek , Chung Wan Kyun , Suh Il Hong
Published: July 2002

Model based disturbance compensating methods such as disturbance observer, robust control with adaptive algorithm, enhanced internal model control are well known control structures for robust motion controller which can satisfy desired performance and robustness of high-speed/high-accuracy positioning systems. In this paper, these are analyzed in the unified framework and their design method is proposed. To do this, a generalized disturbance attenuation framework named RIC (robust internal-loop compensator) structure is introduced. Through parameterization based on RIC, it is shown that there are inherent equivalences in their structures and the proposed RIC gives a general design framework for the model based disturbance compensating methods. Through simulation, the proposed method is verified.
A Finite Element Method for Mechanical Response of Hair Cell Ciliary Bundles
Authors: Cotton John R. , Wallace Grant J.
Published: July 2002

This paper describes the development of a methodology for performing a mechanical analysis of hair cell ciliary bundles. The cilia were modeled as shear deformable beams, and interconnections were modeled as two-force members. These models were incorporated into software, which performs a finite element analysis of a user-defined bundle. The algorithm incorporates aspects of the bundle such as geometric realignment and buckling of compressed side links. A sample bundle is introduced and results of modeling it are presented. [S0148-0731(00)00801-3]
The Trade-Off Between N2, NO, and N2O Under Fluidized Bed Combustor Conditions
Authors: Wartha C. , Winter F. , Hofbauer H.
Published: July 2002

NO and N2O are harmful pollutants. Under fluidized bed combustor conditions, the nitrogen of the solid fuel is partly converted to these species. The trade-off between N2, NO, and N2O depends on the fuel and fuel characteristics, the complex homogeneous and heterogeneous formation and destruction paths, temperature and residence times, and so forth. Because of these complex interrelations, it is necessary to study these processes separately and to analyze their relative importance. To obtain a better understanding of the formation and destruction paths of NO and N2O, comprehensive studies have been performed in a laboratory-scale fluidized bed reactor optimized to obtain formation rates. The influence of the temperature and radicals on the NO and N2O formation from HCN and NH3 and destruction reactions were studied. The results show that N2O is formed only from HCN. Oxidation of NH3 forms NO and N2, HCN forms NO, N2O, and N2. Typically, 30 to 70 percent of NH3 are converted to N2, depending on bed temperature. In the case of HCN, only 5 to 25 percent are converted to N2. At temperatures below 800°C, NO reacts with CH4 oxidation products to NO2. Tests with HCN show that HCN conversion starts already at 700°C in the fluidized bed, N2O is formed in significant amounts only in the presence of CH4. The results of the NO and N2O destruction tests show that the thermal mechanism is of minor importance. At 900°C, N2O destruction with H radicals can be seen. N2O formation shows a maximum at 850°C. The gas reaction studies were used to understand the NH3, HCN, NO, and N2O single-particle formation characteristics of coke, bituminous coal, peat, and spruce wood under fluidized bed combustor conditions. [S0195-0738(00)00702-0]
A New Technique for Identifying Synchronous Resonances Using Tip-Timing
Authors: Heath Steve
Published: July 2002

Non-contact measurement of vibration at turbomachinery rotor blade tips using blade tip-timing has become an industry-standard procedure. Current research focuses on analysis methods for interpretation of the measured vibration data from a limited number of probes. The methods are classified by the form of the vibration they can identify. Identification of asynchronous response amplitude and frequency is well documented. Whilst a method for identifying maximum synchronous resonance amplitude has existed since the early 1970s, there is no published evidence of a method for directly identifying frequency or engine order using a small number of probes. This paper presents a new analysis method for identifying synchronous resonance engine order using two tip-timing vibration measurements. The measurements are made at different locations on the turbomachinery casing using a minimum of two probes. A detailed description of the method and results from its practical application are given. The potential of the method to identify the amplitude and frequency of close modes, not possible with current methods, is demonstrated. The effect of blade mistuning on the accuracy of the method is investigated. Existing synchronous response analysis methods and the new method presented here give the response amplitude and frequency after the resonance has been traversed. Real-time identification of synchronous response amplitude and frequency would allow tip-timing to be used as a safety monitor of all blades. Real-time methods, their limitations and practical application are discussed. The future use of tip-timing as the dominant vibration measurement system is discussed with reference to experience on measurements made solely with tip-timing on assemblies with undefined vibration characteristics. [S0742-4795(00)02602-8]
Limitations of Statistical Design of Experiments Approaches in Engineering Testing
Authors: Deaconu Stelu , Coleman Hugh W.
Published: July 2002

A hypothetical experiment and Monte Carlo simulations were used to examine the effectiveness of statistical design of experiments methods in identifying from the experimental data the correct terms in postulated regression models for a variety of experimental conditions. Two analysis of variance techniques (components of variance and pooled mean square error) combined with F-test statistics were investigated with first-order and second-order regression models. It was concluded that there are experimental conditions for which one or the other of the procedures results in model identification with high confidence, but there are also other conditions in which neither procedure is successful. The ability of the statistical approaches to identify the correct models varies so drastically, depending on experimental conditions, that it seems unlikely that arbitrarily choosing a method and applying it will lead to identification of the effects that are significant with a reasonable degree of confidence. It is concluded that before designing and conducting an experiment, one should use simulations of the proposed experiment with postulated truths in order to determine which statistical design of experiments approach, if any, will identify the correct model from the experimental data with an acceptable degree of confidence. In addition, no significant change in the effectiveness of the methods in identifying the correct model was observed when systematic uncertainties of up to 10 percent in the independent variables and in the response were introduced into the simulations. An explanation is that the systematic errors in the simulation data caused a shift of the whole response surface up or down from the true value, without a significant change in shape. [S0098-2202(00)03102-3]
The Use of an Organic Self-Assembled Monolayer Coating to Promote Dropwise Condensation of Steam on Horizontal Tubes
Authors: Das A. K. , Kilty H. P. , Marto P. J. , Andeen G. B. , Kumar A.
Published: July 2002

Hydrophobic coatings have been created through self-assembled monolayers (SAMs) on gold, copper, and copper-nickel alloy surfaces that enhance steam condensation through dropwise condensation. The monolayer is formed by chemisorption of alkylthiols on these metal surfaces. Due to their negligible thickness (10–15 Å), SAMs have negligible heat transfer resistance, and involve a minuscule amount of the organic material to pose any contamination problem to the system from erosion of the coating. The coating was applied directly to copper and 90/10 copper-nickel tubes, and to previously gold-sputtered aluminum tubes. The quality of the drops on SAMs, based on visual observation, was found to be similar for the three surfaces, with the gold surface showing a slight superiority. When compared to complete filmwise condensation, the SAM coating increased the condensation heat transfer coefficient by factors of 4 for gold-coated aluminum, and by about 5 for copper and copper-nickel tubes, under vacuum operation (10 kPa). The respective enhancements under atmospheric conditions were about 9 and 14. Comparatively, the heat transfer coefficient obtained with a bare gold surface (with no organic coating) was 2.5 times that of the filmwise condensation heat transfer coefficient under vacuum, and 3.4 at atmospheric conditions. [S0022-1481(00)02502-0]