bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental and Modeling Study of Humid Air Premixed Flames
Authors: Bhargava Anuj , Colket Med , Sowa William , Casleton Kent , Maloney Dan
Published: July 2002

An experimental and modeling study has been performed jointly by UTRC and DOE-FETC to determine the effect of humidity in the combustion air on emissions and stability limits of gas turbine premixed flames. This study focuses on developing gas turbine combustor design criteria for the Humid Air Turbine (HAT) cycle. The experiments were conducted at different moisture levels (0 percent, 5 percent, 10 percent, and 15 percent by mass in the air), at a total pressure of 200 psi, pilot levels (0 percent, 1 percent, 3 percent, and 5 percent total fuel), and equivalence ratio (0.4 to 0.8 depending on the moisture levels). The moisture levels were achieved by injecting steam into dry air well upstream of the fuel-air premixing nozzle. Computations were made for comparison to the experiments using GRI Mech 2.11 kinetics and thermodynamic database for modeling the flame chemistry. A Perfectly Stirred Reactor (PSR) network code was used to create a network of PSRs to simulate the flame. Excellent agreement between the measured and modeled NOx (5–10 percent) was obtained. Trends of added moisture reducing NOx and the effects of equivalence ratio and piloting level were well predicted. The CO predictions were higher by about 30–50 percent. The CO discrepancies are attributed to in-probe oxidation. The agreement between the data and model predictions over a wide range of conditions indicate the consistency and reliability of the measured data and usefulness of the modeling approach. An analysis of NOx formation revealed that at constant equilibrium temperature, Teq, the presence of steam leads to lower O-atom concentration which reduces “Zeldovich and N2O” NOx while higher OH-atom concentration reduces “Fenimore” NOx.[S0742-4795(00)00703-1]
Thermoeconomic Analysis of Gas Turbine Based Cycles
Authors: Massardo A. F. , Scialo` M.
Published: July 2002

The thermoeconomic analysis of gas turbine based cycles is presented and discussed in this paper. The thermoeconomic analysis has been performed using the ThermoEconomic Modular Program (TEMP V.5.0) developed by Agazzani and Massardo (1997). The modular structure of the code allows the thermoeconomic analysis for different scenarios (turbine inlet temperature, pressure ratio, fuel cost, installation costs, operating hours per year, etc.) of a large number of advanced gas turbine cycles to be obtained in a fast and reliable way. The simple cycle configuration results have been used to assess the cost functions and coefficient values. The results obtained for advanced gas turbine based cycles (inter-cooled, re-heated, regenerated and their combinations) are presented using new and useful representations: cost versus efficiency, cost versus specific work, and cost versus pressure ratio. The results, including productive diagram configurations, are discussed in detail and compared to one another. [S0742-4795(00)01903-7]
Effects of Alloy Composition on the Performance of Yttria Stabilized Zirconia—Thermal Barrier Coatings
Authors: Kimmel Josh , Mutasim Zaher , Brentnall William
Published: July 2002

Thermal barrier coatings (TBCs) provide an alloy surface temperature reduction when applied to turbine component surfaces. Thermal barrier coatings can be used as a tool for the designer to augment the power and/or enhance the efficiency of gas turbine engines. TBCs have been used successfully in the aerospace industry for many years, with only limited use for industrial gas turbine applications. Industrial gas turbines operate for substantially longer cycles and time between overhauls, and thus endurance becomes a critical factor. There are many factors that affect the life of a TBC including the composition and microstructure of the base alloy and bond coating. Alloys such as Mar-M 247, CMSX-4, and CMSX-10 are materials used for high temperature turbine environments, and usually require protective and/or thermal barrier coatings for increased performance. Elements such as hafnium, rhenium, and yttrium have shown considerable improvements in the strength of these alloys. However, these elements may result in varying effects on the coatability and environmental performance of these alloys. This paper discusses the effects of these elements on the performance of thermal barrier coatings. [S0742-4795(00)02603-X]
Effect of Wake Disturbance Frequency on the Secondary Flow Vortex Structure in a Turbine Blade Cascade
Authors: Murawski Christopher G. , Vafai Kambiz
Published: July 2002

An experimental study of the effect of wake disturbance frequency on the secondary flow vortices in a two-dimensional linear cascade is presented. The flow Reynolds numbers, based on exit velocity and suction side surface length were 25,000, 50,000 and 85,000. Secondary flow was visualized by injecting smoke into the boundary layer and illuminating it with a laser light sheet located at the exit of the cascade. To simulate wakes from upstream blade rows, a set of spanwise cylinders were traversed across the front of the blade row. The flow visualization results with a single wake disturbance reveal that the recovery time of the secondary flow vortex structure decreases as the wake traverse velocity is increased. The results of flow visualization with multiple wakes showed that wake disturbance frequencies below the axial chord flow frequency allowed complete recovery of the secondary flow vortex structure before the next wake encounters the blade leading edge. Wake disturbance frequencies that exceeded the axial chord flow frequency resulted in no observable recovery of the secondary flow vortex structure. Axial chord flow frequency is defined as the axial velocity in the cascade divided by the axial chord length of the turbine blade. [S0098-2202(00)02203-3]
Molecular Dynamics Study of Solid Thin-Film Thermal Conductivity
Authors: Lukes J. R. , Li D. Y. , Liang X.-G. , Tien C.-L.
Published: July 2002

This study uses the molecular dynamics computational technique to investigate the thermal conductivity of solid thin films in the direction perpendicular to the film plane. In order to establish a benchmark reference, the computations are based on the widely used Lennard-Jones argon model due to its agreement with experimental liquid-phase data, its physically meaningful parameters, and its simple two-body form. Thermal conductivity increases with film thickness, as expected from thin-film experimental data and theoretical predictions. The calculated values are roughly 30 percent higher than anticipated. Varying the boundary conditions, heat flux, and lateral dimensions of the films causes no observable change in the thermal conductivity values. The present study also delineates the conditions necessary for meaningful thermal conductivity calculations and offers recommendations for efficient simulations. This work shows that molecular dynamics, applied under the correct conditions, is a viable tool for calculating the thermal conductivity of solid thin films. More generally, it demonstrates the potential of molecular dynamics for ascertaining microscale thermophysical properties in complex structures. [S0022-1481(00)02303-3]
Nonlinear Vibrations and Multiple Resonances of Fluid-Filled, Circular Shells, Part 2: Perturbation Analysis
Authors: Pellicano F. , Amabili M. , Vakakis A. F.
Published: July 2002

The nonlinear ordinary differential equations describing the dynamics of a fluid filled circular cylindrical shell, obtained in Part 1 of the present study, is studied by using a second order perturbation approach and direct simulations. Strong modal interactions are found when the structure is excited with small resonant loads. Modal interactions arise in the whole range of vibration amplitude, showing that the internal resonance condition makes the system non-linearizable even for extremely small amplitudes of oscillation. Stationary and nonstationary oscillations are observed and the complex nature of modal interactions is accurately analyzed. No chaotic motion is observed in the case of 1:1:1:2 internal resonance studied. [S0739-3717(00)01304-0]
Electrode-Ceramic Interfacial Cracks in Piezoelectric Multilayer Materials
Authors: Ru C.
Published: July 2002

A thin electrode layer embedded at the interface of two piezoelectric materials represents a common feature of many electroceramic multilayer devices. The analysis of interface cracks between the embedded electrode layer and piezoelectric ceramic leads to a nonstandard mixed boundary value problem which likely prevents a general analytical solution. The present work shows that the associated mixed boundary value problem does indeed admit an exact elementary solution for a special case of major practical interest in which the two piezoelectric half-planes are poled in opposite directions perpendicular to the electrode layer. In this case, it is found that oscillatory singularity disappears, in spite of the unsymmetric characters of the problem, and electroelastic fields exhibit power singularities. Particular emphasis is placed on the near-tip singular stresses along the bonded interface. The results show that tensile stress exhibits the square root singularity along the interface whereas shear stress exhibits the dominant-order nonsquare root singularity. In addition, the present model indicates that a pure electric-field loading could induce the dominant-order singular shear stress directly ahead of the interface crack tip. [S0021-8936(00)00602-4]
Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gages
Authors: Guo S. M. , Lai C. C. , Jones T. V. , Oldfield M. L. G. , Lock G. D. , Rawlinson A. J.
Published: July 2002

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled three-dimensional nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gages (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet free-stream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modeled to represent engine conditions by using a heavy “foreign gas” (30.2 percent SF6 and 69.8 percent Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented. The surfaces of interest are coated with wide-band thermochromic liquid crystals, which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of color is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in-service turbine blades and vanes, increases the heat transfer coefficient by up to 50 percent over the smooth surface level. The film cooling effectiveness is influenced less by the roughness. [S0889-504X(00)00804-7]
Rotating Tapered Composite Shafts: Forced Torsional and Extensional Motions and Static Strength
Authors: Kim W. , Argento A. , Scott R. A.
Published: July 2002

Forced torsional and extensional motions and static strength of rotating, tapered, filament-wound composite shafts subject to deflection-dependent cutting forces typical of end-milling and boring operations are studied. The general Galerkin method is used to satisfy spatial dependence in the equations of motion and direct numerical integration is used to determine the system’s response. The maximum stress criterion is used to investigate static failure.
Computer Simulation of Intraventricular Flow and Pressure Gradients During Diastole
Authors: Vierendeels J. A. , Riemslagh K. , Dick E. , Verdonck P. R.
Published: July 2002

A two-dimensional axisymmetric computer model is developed for the simulation of the filling flow in the left ventricle (LV). The computed results show that vortices are formed during the acceleration phases of the filling waves. During the deceleration phases these are amplified and convected into the ventricle. The ratio of the maximal blood velocity at the mitral valve (peak E velocity) to the flow wave propagation velocity (WPV) of the filling wave is larger than 1. This hemodynamic behavior is also observed in experiments in vitro (Steen and Steen, 1994, Cardiovasc. Res., 28, pp. 1821–1827) and in measurements in vivo with color M-mode Doppler echocardiography (Stugaard et al., 1994, J. Am. Coll. Cardiol., 24, 663–670). Computed intraventricular pressure profiles are similar to observed profiles in a dog heart (Courtois et al., 1988, Circulation, 78, pp. 661–671). The long-term goal of the computer model is to study the predictive value of noninvasive parameters (e.g., velocities measured with Doppler echocardiography) on invasive parameters (e.g., pressures, stiffness of cardiac wall, time constant of relaxation). Here, we show that higher LV stiffness results in a smaller WPV for a given peak E velocity. This result may indicate an inverse relationship between WPV and LV stiffness, suggesting that WPV may be an important noninvasive index to assess LV diastolic stiffness, LV diastolic pressure and thus atrial pressure (preload). [S0148-0731(00)01606-X]
Three-Dimensional Numerical Prediction of the Hydrodynamic Loads and Motions of Offshore Structures
Authors: Schulz Karl W. , Kallinderis Yannis
Published: July 2002

A generalized numerical method for solution of the incompressible Navier-Stokes equations in three-dimensions has been developed. This solution methodology allows for the accurate prediction of the hydrodynamic loads on offshore structures, which is then combined with a rigid body structural response to address the flow-structure coupling which is often present in offshore applications. Validation results using this method are first presented for fixed structures which compare the drag coefficients of sphere and cylinder geometries to experimental measurements over a range of subcritical Reynolds numbers. Additional fixed structure results are then presented which explore the influence of aspect ratio effects on the lift and drag coefficients of a bare circular cylinder. Finally, the spanwise flow variations between a fixed and freely vibrating cylindrical structure are compared to demonstrate the ability of the flow-structure method to correctly predict correlation length increases for a vibrating structure. [S0892-7219(00)00904-3]
Theoretical Development and Experimental Validation of Local Volume Displacement Sensors for a Vibrating Beam
Authors: Zahui Marcellin B. , Kamman James W. , Naghshineh Koorosh
Published: July 2002

Further development of local volume displacement sensors is presented. This development supports the implementation of noise control techniques that are based on minimization of local volume displacements, velocities, or accelerations of a vibrating structure. In this paper, we present a general methodology for the development of local volume displacement sensors for vibrating beams using P_olyV_inyliD_ene F_luoride (PVDF). This methodology was verified experimentally for a clamped beam. The local volume displacement measured using a single PVDF sensor matched the local volume displacement found using multiple accelerometer measurements. The resulting sensors span the entire length of the beam. They have a quadratic shape over that portion of the beam whose volume displacement is desired, and they have a linear shape over all other sections. Sensor design issues for different beam boundary conditions are discussed along with a presentation of some sample sensor shapes for various beam segments and boundary conditions.
On the Theory of Thermal Elastohydrodynamic Lubrication at High Slide-Roll Ratios—Circular Glass-Steel Contact Solution at Opposite Sliding
Authors: Guo Feng , Yang Peiran , Qu Shiyue
Published: July 2002

A full numerical solution for the thermal EHL problem in circular contact formed by steel-glass conjunctions with slide-roll ratios larger than 2 has been carried out. An anomalous film profile, which is similar to that reported by Kaneta et al. (1996), has been obtained. The numerical results by the authors, involving three basic kinds of film profiles, the kinematic conditions for the formation of dimples, and the variations of dimples and traction behavior with operating conditions, have been carefully compared with the experiments by Kaneta et al., and provided a sound theoretical evidence of the dimple phenomena under steady-state conditions. The present study indicates that the temperature-viscosity-wedge effect seems to be an essential mechanism for the dimple phenomena.
Local Heat Transfer and Flow Structure on and Above a Dimpled Surface in a Channel
Authors: Mahmood G. I. , Hill M. L. , Nelson D. L. , Ligrani P. M. , Moon H.-K. , Glezer B.
Published: July 2002

Experimental results, measured on and above a dimpled test surface placed on one wall of a channel, are given for Reynolds numbers from 1250 to 61,500 and ratios of air inlet stagnation temperature to surface temperature ranging from 0.68 to 0.94. These include flow visualizations, surveys of time-averaged total pressure and streamwise velocity, and spatially resolved local Nusselt numbers, which are measured using infrared thermography, used in conjunction with energy balances, thermocouples, and in situ calibration procedures. The ratio of channel height to dimple print diameter is 0.5. Flow visualizations show vortical fluid and vortex pairs shed from the dimples, including a large upwash region and packets of fluid emanating from the central regions of each dimple, as well as vortex pairs and vortical fluid that form near dimple diagonals. These vortex structures augment local Nusselt numbers near the downstream rims of each dimple, both slightly within each depression, and especially on the flat surface just downstream of each dimple. Such augmentations are spread over larger surface areas and become more pronounced as the ratio of inlet stagnation temperature to local surface temperature decreases. As a result, local and spatially averaged heat transfer augmentations become larger as this temperature ratio decreases. This is due to the actions of vortical fluid in advecting cool fluid from the central parts of the channel to regions close to the hotter dimpled surface.
Finite Amplitude Azimuthal Shear Waves in a Compressible Hyperelastic Solid
Authors: Haddow J. B. , Jiang L.
Published: July 2002

Lagrangian equations of motion for finite amplitude azimuthal shear wave propagation in a compressible isotropic hyperelastic solid are obtained in conservation form with a source term. A Godunov-type finite difference procedure is used along with these equations to obtain numerical solutions for wave propagation emanating from a cylindrical cavity, of fixed radius, whose surface is subjected to the sudden application of a spatially uniform azimuthal shearing stress. Results are presented for waves propagating radially outwards; however, the numerical procedure can also be used to obtain solutions if waves are reflected radially inwards from a cylindrical outer surface of the medium. A class of strain energy functions is considered, which is a compressible generalization of the Mooney-Rivlin strain energy function, and it is shown that, for this class, an azimuthal shear wave can not propagate without a coupled longitudinal wave. This is in contrast to the problem of finite amplitude plane shear wave propagation with the neo-Hookean generalization, for which a shear wave can propagate without a coupled longitudinal wave. The plane problem is discussed briefly for comparison with the azimuthal problem.
Component-Mode-Based Reduced Order Modeling Techniques for Mistuned Bladed Disks—Part I: Theoretical Models
Authors: Bladh R. , Castanier M. P. , Pierre C.
Published: July 2002

Component mode synthesis (CMS) techniques are widely used for dynamic analyses of complex structures. Significant computational savings can be achieved by using CMS, since a modal analysis is performed on each component structure (substructure). Mistuned bladed disks are a class of structures for which CMS is well suited. In the context of blade mistuning, it is convenient to view the blades as individual components, while the entire disk may be treated as a single component. Individual blade mistuning may then be incorporated into the CMS model in a straightforward manner. In this paper, the Craig–Bampton (CB) method of CMS is formulated specifically for mistuned bladed disks, using a cyclic disk description. Then a novel secondary modal analysis reduction technique (SMART) is presented: a secondary modal analysis is performed on a CB model, yielding significant further reduction in model size. In addition, a straightforward non-CMS method is developed in which the blade mistuning is projected onto the tuned system modes. Though similar approaches have been reported previously, here it is generalized to a form that is more useful in practical applications. The theoretical models are discussed and compared from both computational and practical perspectives. It is concluded that using SMART, based on a CB model, has tremendous potential for highly efficient, accurate modeling of the vibration of mistuned bladed disks.
Transportation Fuel Substitutes Derived From Biomass
Authors: Gouli S. , Serdari A. , Stournas S. , Lois E.
Published: July 2002

This paper describes some of the recent work carried out in our laboratory regarding the effects of novel nitrogen compounds in gasoline and diesel fuel on ignition quality and on pollutant emissions. Emphasis is given in studying chemical structures that can be derived from biomass (renewable raw materials). Our approach was to investigate chemical structures that can be derived from biomass, by studying the performance of possible gasoline and diesel extenders as gaged by ignition quality, and also by testing their effectiveness in reducing exhaust emissions under various operating conditions.
Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions
Authors: Volino Ralph J. , Hultgren Lennart S.
Published: July 2002

Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2 and 7 percent) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains nonturbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions, transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re=50,000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence, and intermittency profiles are presented.
Hysteretic Behavior of a Bar Under Repeated Axial Loading: An Extended History
Authors: Yoshida N. , Nonaka T.
Published: July 2002

Analytical study is made of an elastic-perfectly plastic bar under repeated axial loading. A previous formulation on a pin-ended bar is extended here to include the effects of load eccentricity and rotational constraint at the bar ends. Basic equations are derived, based on the assumptions of planar and small deflection, and of symmetry with respect to the bar center. The end spring is allowed to yield. Numerical examples are presented to demonstrate the application of the basic equations, and adequacy is shown for any specified history of axial displacement. Diagrammatical representation of state variation provides a better understanding of the hysteretic behavior as well as the applicability of the basic equations.
Modeling Atomization of High-Pressure Diesel Sprays
Authors: Bianchi G. M. , Pelloni P. , Corcione F. E. , Allocca L. , Luppino F.
Published: July 2002

This paper deals with a numerical and experimental characterization of a high-pressure diesel spray injected by a common-rail injection system. The experiments considered a free non-evaporating spray and they were performed in a vessel reproducing the practical density that characterizes a D.I. diesel engine at injection time. The fuel was supplied at high pressure by a common-rail injection system with a single hole tip. The computations have been carried out by using both the TAB model and a hybrid model that allows one to describe both liquid jet atomization and droplet breakup. In order to validate the breakup model, an extensive comparison between data and numerical predictions has been carried out in terms of spray penetration, Sauter mean diameter, near and far spray cone angles, and spray structure.
A Novel Mini Calibrator for Thermochromic Liquid Crystals
Authors: Elkins Christopher J. , Fessler John , Eaton John K.
Published: July 2002

A small calibrator has been constructed to facilitate wide-band liquid crystal temperature measurements on complex, curved surfaces. The calibrator’s size, 21.3 mm by 20.3 mm by 10.0 mm thick, makes it ideal for in-situ calibrations at multiple sites on curved surfaces. Its design utilizes the heating/cooling ability of a thermoelectric cooler, and its temperature is quickly and accurately controlled by computer. To test the calibrator’s accuracy, a liquid crystal sample was calibrated. Subsequent comparisons to thermistor measurements of a uniform temperature copper block painted with liquid crystals showed the calibration to be accurate to +/−0.1°C between the red start and the approximate blue start temperatures, and the maximum error was less than +/−0.3°C in the dark blue/violet region.
Effect of Internal Gear Flexibility on the Quasi-Static Behavior of a Planetary Gear Set
Authors: Kahraman Ahmet , Vijayakar Sandeep
Published: July 2002

Effect of flexibility of an internal gear on the quasi-static behavior of a planetary gear set is investigated. A state-of-the-art finite elements/semi-analytical nonlinear contact mechanics formulation is employed to model a typical automotive automatic transmission planetary unit. The model considers each gear as deformable bodies and meshes them to predict loads, stresses and deformations of the gears. Actual support and spline conditions are included in the model. The rim thickness of the internal gear is varied relative to the tooth height and gear deflections and bending stresses are quantified as a function of rim thickness. Influence of rim thickness on the load sharing amongst the planets is also investigated with and without floating sun gear condition. The results are discussed in detail and guidelines regarding the design of a planetary internal gear are presented.
Modeling and Experimental Validation of Superconductor Tape Rolling
Authors: Pandheeradi M. , Vaze S. P. , Yuan D.-W. , Kuhn H. A.
Published: July 2002

Efficient, defect-free manufacturing of high-temperature superconducting (HTS) wires and tapes is critical to a variety of defense and electrical power applications. To contribute to the improvement of these manufacturing operations, an analytical and experimental study of the early stages of the multipass rolling process for transforming HTS wires into tapes was conducted. The rolling process was simulated by a three-dimensional (3D) finite element model that uses the Drucker-Prager Cap plasticity model to represent the powder core and a Von-Mises plasticity model with isotropic hardening to represent the silver sheath. The predicted cross-sectional geometry of the tapes is compared with experiments. The results show that the tape cross-sectional geometry and powder core sizes can be predicted accurately. Further, alternate boundary conditions were found to have minimal effect on the predicted cross-sectional geometry for the range of reductions considered, even though the frictional shear stress distributions were significantly different.
Anisotropic and Inhomogeneous Tensile Behavior of the Human Anulus Fibrosus: Experimental Measurement and Material Model Predictions
Authors: Elliott Dawn M. , Setton Lori A.
Published: July 2002

The anulus fibrosus (AF) of the intervertebral disc exhibits spatial variations in structure and composition that give rise to both anisotropy and inhomogeneity in its material behaviors in tension. In this study, the tensile moduli and Poisson’s ratios were measured in samples of human AF along circumferential, axial, and radial directions at inner and outer sites. There was evidence of significant inhomogeneity in the linear-region circumferential tensile modulus (17.4±14.3 MPa versus 5.6±4.7 MPa, outer versus inner sites) and the Poisson’s ratio ν21 (0.67±0.22 versus 1.6±0.7, outer versus inner), but not in the axial modulus (0.8±0.9 MPa) or the Poisson’s ratios ν12 (1.8±1.4) or ν13 (0.6±0.7). These properties were implemented in a linear anisotropic material model of the AF to determine a complete set of model properties and to predict material behaviors for the AF under idealized kinematic states. These predictions demonstrate that interactions between fiber populations in the multilamellae AF significantly contribute to the material behavior, suggesting that a model for the AF as concentric and physically isolated lamellae may not be appropriate.
Computer Identification of Structural Weaknesses in Locally Anisotropic Polycrystalline Materials
Authors: Li Xu-Dong
Published: July 2002

Computer experiments were performed to investigate behavior of mesoscopic stress responses in a simulated polycrystalline material sample containing a fairly large number of constituent grains for a number of polycrystalline materials. Kro¨ner-Kneer structure-based model was adopted and refined to provide an efficacious numerical approach to local mesoscopic stresses. The approach is developed on a concept of average fields of grains for arbitrarily polygon-shaped grains. Three criteria were proposed for classifying speculated material structure weaknesses in all simulated material samples. It is found that material structure weaknesses can be well correlated by defined “Orientation-Geometry Factor” and “Relevance Parameter.” Not only grain-orientation but also grain geometry exerts strong influences on mesoscopic stress distribution, hence the distribution of material structure weaknesses in simulated polycrystalline material samples. Computer experiments lead to correlated relationships that links material structure weaknesses with local microstructure, and a database for discrimination of material structure weaknesses in the material samples. The homogenization of materials with locally anisotropic microstructure is also discussed.
Mechanisms of High-pH and Near-Neutral-pH SCC of Underground Pipelines
Authors: Beavers John A. , Harle Brent A.
Published: July 2002

This paper provides an overview of mechanisms for high-pH and near-neutral pH stress corrosion cracking of underground pipelines. Characteristics and historical information on both forms of cracking are discussed. This information is then used to support proposed mechanisms for crack initiation and growth.
Monte Carlo Study of Phonon Transport in Solid Thin Films Including Dispersion and Polarization
Authors: Mazumder Sandip , Majumdar Arunava
Published: July 2002

The Boltzmann Transport Equation (BTE) for phonons best describes the heat flow in solid nonmetallic thin films. The BTE, in its most general form, however, is difficult to solve analytically or even numerically using deterministic approaches. Past research has enabled its solution by neglecting important effects such as dispersion and interactions between the longitudinal and transverse polarizations of phonon propagation. In this article, a comprehensive Monte Carlo solution technique of the BTE is presented. The method accounts for dual polarizations of phonon propagation, and non-linear dispersion relationships. Scattering by various mechanisms is treated individually. Transition between the two polarization branches, and creation and destruction of phonons due to scattering is taken into account. The code has been verified and evaluated by close examination of its ability or failure to capture various regimes of phonon transport ranging from diffusive to the ballistic limit. Validation results show close agreement with experimental data for silicon thin films with and without doping. Simulation results show that above 100 K, transverse acoustic phonons are the primary carriers of energy in silicon.
Confinement and Suppression of Structural Vibrations
Authors: Choura Slim , Yigit Ahmet S.
Published: July 2002

A feedback strategy, aiming at confining and suppressing simultaneously the vibratory motion in flexible structures, is proposed. It is assumed that the structure consists of parts that are sensitive to vibration. The proposed strategy makes use of control inputs whose number is less than or equal to that of the dimension of the discretized model. The design objective is to devise a feedback scheme that leads to transferring the vibrational energy from the sensitive parts to the remaining parts of the structure. In order to keep away from the build-up of transferred energy in the nonsensitive parts, the feedback scheme considers, along with the confinement, the suppression of vibration in both the sensitive and nonsensitive parts. The proposed strategy also accounts for the presence of persistent excitations. A finite element model of a cantilever beam is used to show the viability of the proposed strategy.
Horizontal Well Path Planning and Correction Using Optimization Techniques
Authors: McCann Roger C. , Suryanarayana P. V. R.
Published: July 2002

We present a procedure that uses nonlinear optimization theory to plan complex, three-dimensional well paths and path corrections while drilling. The problem of hitting a 3-D target is posed as seeking a profile that optimizes some well-defined objective function (the optimality criterion) subject to equality and inequality constraints. The well path is idealized to contain a finite combination of turn and straight sections. Operational restrictions translate into inequality constraints, and target restrictions translate into equality constraints. Several optimality criteria may be chosen, and appropriate choices are discussed. In this work, we choose optimization with respect to user preferred parameters as the criterion. The resulting nonlinear optimization problem is solved using a sequential gradient-restoration algorithm (SGRA), with scaling and optimal step-size selection. The optimization problem formulation and the solution procedure are described. The procedure is robust, efficient, and clearly superior to trial-and-error heuristic techniques that are commonly used to plan well paths today. A computer program based on this technique has been developed and successfully used. Two examples are included to illustrate the procedure. It is concluded that nonlinear optimization is a powerful and versatile mathematical tool that can be used for planning better, optimal well paths, and can be extended to several other drilling and production problems.
Full-Coverage Film Cooling With Short Normal Injection Holes
Authors: Harrington Mark K. , McWaters Marcus A. , Bogard David G. , Lemmon Christopher A. , Thole Karen A.
Published: July 2002

An experimental and computational investigation was conducted on the film cooling adiabatic effectiveness of a flat plate with full coverage film cooling. The full coverage film cooling array was comprised of ten rows of coolant holes, arranged in a staggered pattern, with short L/D=1, normal coolant holes. A single row of cooland holes was also examined to determine the accuracy of a superposition prediction of the full coverage adiabatic effectiveness performance. Large density coolant jets and high mainstream turbulence conditions were utilized to simulate realistic engine conditions. High-resolution adiabatic effectiveness measurements were obtained using infrared imaging techniques and a large-scale flat plate model. Optimum adiabatic effectiveness was found to occur for a blowing ratio of M=0.65. At this blowing ratio separation of the coolant jet immediately downstream of the hole was observed. For M=0.65, the high mainstream turbulence decreased the spatially averaged effectiveness level by 12 percent. The high mainstream turbulence produced a larger effect for lower blowing ratios. The superposition model based on single row effectiveness results over-predicted the full coverage effectiveness levels.
A Parametric Analysis of the Transient Forced Response of Noncontacting Coned-Face Gas Seals
Authors: Green Itzhak , Barnsby Roger M.
Published: July 2002

A properly designed mechanical face seal must satisfy two requirements: (1) the seal must be stable, and (2) the seal forced response must be such that the stator tracks the misaligned rotor with the smallest clearance possible, with the smallest relative tilt, and with the largest minimum film thickness. The stability issue was investigated in a previous paper. Here a numerical solution is presented for the transient response of a noncontacting gas lubricated face seal that is subjected to stator and rotor forcing misalignments. The seal dynamic response is obtained in axial and angular modes of motion in a coupled analysis where the Reynolds equation and the equations of motion are solved simultaneously. The steady-state response is first identified for a reference case. Subsequently a parametric study is performed to gauge the influence of the various seal effects, such as speeds, inner to outer radii ratios, face coning heights, pressure drops, support stiffness and damping, and forcing misalignments. The transient responses to static stator misalignment and rotor runout are given, showing that properly designed coned face seals can operate in a stable mode with the stator tracking dynamically a misaligned rotor.
On Fractal Cracks in Micropolar Elastic Solids
Authors: Yavari A. , Sarkani S. , Moyer, E. T.
Published: July 2002

In this paper we review the fracture mechanics of smooth cracks in micropolar (Cosserat) elastic solids. Griffith’s fracture theory is generalized for cracks in micropolar solids and shown to have two possible forms. The effect of fractality of fracture surfaces on the powers of stress and couple-stress singularity is studied. We obtain the orders of stress and couple-stress singularities at the tip of a fractal crack in a micropolar solid using dimensional analysis and an asymptotic method that we call “method of crack-effect zone.” It is shown that orders of stress and couple-stress singularities are equal to the order of stress singularity at the tip of the same fractal crack in a classical solid.
Comprehensive Approach to Verification and Validation of CFD Simulations—Part 1: Methodology and Procedures
Authors: Stern Fred , Wilson Robert V. , Coleman Hugh W. , Paterson Eric G.
Published: July 2002

Part 1 of this two-part paper presents a comprehensive approach to verification and validation methodology and procedures for CFD simulations from an already developed CFD code applied without requiring availability of the source code for specified objectives, geometry, conditions, and available benchmark information. Concepts, definitions, and equations derived for simulation errors and uncertainties provide the overall mathematical framework. Verification is defined as a process for assessing simulation numerical uncertainty and, when conditions permit, estimating the sign and magnitude of the numerical error itself and the uncertainty in that error estimate. The approach for estimating errors and uncertainties includes (1) the option of treating the numerical error as deterministic or stochastic, (2) the use of generalized Richardson extrapolation for J input parameters, and (3) the concept of correction factors based on analytical benchmarks, which provides a quantitative metric to determine proximity of the solutions to the asymptotic range, accounts for the effects of higher-order terms, and are used for defining and estimating errors and uncertainties. Validation is defined as a process for assessing simulation modeling uncertainty by using benchmark experimental data and, when conditions permit, estimating the sign and magnitude of the modeling error itself. The approach properly takes into account the uncertainties in both the simulation and experimental data in assessing the level of validation. Interpretation of results of validation efforts both where the numerical error is treated as deterministic and stochastic are discussed. Part 2 provides an example for RANS simulations for a cargo/container ship where issues with regard to practical application of the methodology and procedures and interpretation of verification and validation results are discussed.
Comprehensive Approach to Verification and Validation of CFD Simulations—Part 2: Application for Rans Simulation of a Cargo/Container Ship
Authors: Wilson Robert V. , Stern Fred , Coleman Hugh W. , Paterson Eric G.
Published: July 2002

Part 2 of this two-part paper provides an example case study following the recently developed comprehensive verification and validation approach presented in Part 1. The case study is for a RANS simulation of an established benchmark for ship hydrodynamics using a ship hydrodynamics CFD code. Verification of the resistance (integral variable) and wave profile (point variable) indicates iterative uncertainties much less than grid uncertainties and simulation numerical uncertainties of about 2%S1(S1 is the simulation value for the finest grid). Validation of the resistance and wave profile shows modeling errors of about 8%D (D is the measured resistance) and 6%ζmax(ζmax is the maximum wave elevation), which should be addressed for possible validation at the 3%D and 4%ζmax levels. Reducing the level of validation primarily requires reduction in experimental uncertainties. The reduction of both modeling errors and experimental uncertainties will produce verified and validated solutions at low levels for this application using the present CFD code. Although there are many issues for practical applications, the methodology and procedures are shown to be successful for assessing levels of verification and validation and identifying modeling errors in some cases. For practical applications, solutions are far from the asymptotic range; therefore, analysis and interpretation of the results are shown to be important in assessing variability for order of accuracy, levels of verification, and strategies for reducing numerical and modeling errors and uncertainties.
Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys
Authors: Arakere N. K. , Swanson G.
Published: July 2002

High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE’ N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude [Δτmax] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200°F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component’s resistance to fatigue crack growth without adding additional weight or cost.
Key Inspection Characteristics
Authors: Suri Rajiv , Frey Daniel D. , Otto Kevin N.
Published: July 2002

This paper introduces a technique that can be used in the early manufacturing process design stage to select from among the set of quality characteristics a smaller set that is adequate to ensure a product meets yield specifications. The critical subset of quality characteristics needed to ensure yield are identified, based upon a conditional probability model that ensures all specifications are met, given that the critical subset is met. The approach is demonstrated using a sheet stretch forming manufacturing system from the aerospace industry.