bluuebunny/crossref_metadata_2025 huggingface dataset:
Direction-Dependent Constriction Flow in a Poroelastic Solid: The Intervertebral Disc Valve
Authors: Ayotte D. C. , Ito K. , Perren S. M. , Tepic S.
Published: July 2002

We hypothesize that a direction-dependent flow resistance exists in the intervertebral disc due to constriction flow in the cartilage endplates. A comparison of the hydrostatic pressure in the nucleus of the healthy intervertebral disc during daily loading with the relatively low osmotic swelling pressure during rest, suggests the necessity of such directiondependent flow resistance to ensure that all the fluid exuded from the disc during loading is recovered during rest. A physical model demonstrating the direction-dependent resistance of constriction flow in a poroelastic solid is presented. A finite element model was developed and validated against this physical model. The finite element model showed that decrease of the constriction hole area not only increases the resistance to fluid flow, but also causes the direction-dependency of flow resistance to decrease. Through this mechanism, endplate sclerosis could affect normal daily fluid exchange in the intervertebral disc, resulting in decreased mass transport and/or dehydration of the disc. [S0148-0731(00)00406-4]
Analysis of Bouncing Vibrations of a 2-DOF Model of Tripad Contact Slider Over a Random Wavy Disk Surface
Authors: Iida Kohei , Ono Kyosuke
Published: July 2002

We numerically analyzed the bouncing vibrations of a two-degree-of-freedom (2-DOF) model of a tri-pad contact slider with air bearing pads over a random wavy surface and manifested the design conditions of a contact slider. The effects of the design parameters such as air bearing stiffness, contact damping ratio, the coefficient of friction, and the characteristics of the disk surface waviness on dynamic behavior and the contact sliding ability of the slider have been investigated. As a result, we found that friction force decreases the contact sliding ability at the boundary of the intermittent and continuous contact sliding. We also found that the distance between the rear air bearing center and the contact pad has a significant effect on the contact sliding ability. If the contact pad is apart from the rear air bearing center, the contact pad tends to separate from the disk. Based on this analytical study, we have proposed two design concepts: (1) Make the distance between the rear air bearing center and the contact pad as small as possible; in this case, the larger the rear air bearing stiffness results are, the better the contact ability is; (2) If some distance between the rear air bearing center and the contact pad is inevitable, then make the rear air bearing stiffness much smaller than the contact stiffness.
Experimental Investigation of Mooring Line Loading Using Large and Small-Scale Models
Authors: Kitney Neil , Brown David T.
Published: July 2002

For catenary mooring lines, the relationship between excursion of the point of suspension and the length of suspended line is highly nonlinear. If the point of suspension is then set in motion, the velocity of the line resulting from a change in catenary profile induces additional nonlinear hydrodynamic loading components. The sensitivity of the mooring line to initial and oscillatory conditions results in a complicated tension history at the point of suspension, with line tensions possibly greatly exceeding those predicted by static analyses. This paper presents results from an experimental investigation into the response of a large (1:16) and small (1:70) scale single-chain catenary model mooring line when subject to a comprehensive, and equivalent, range of excitation parameters. Tests were performed at purpose-built test facilities. Small-scale model tests were carried out at University College London (UCL). Large-scale model mooring line tests were completed at the Ship Dynamics Laboratory, Canal de Experiencias Hidrodinamicas de El Pardo (CEHIPAR), Madrid, Spain. Funding for the model tests performed in Spain was provided through the European Union Access to Large Scale Facilities—Training and Mobilisation of Researchers Program.
Constrained Substructure Approach to Optimal Strain Energy Analysis
Authors: Leo Donald J. , Austin Eric M. , Beattie Christopher
Published: July 2002

The chief tool for design of viscoelastic-based damping treatments over the past 20 years has been the modal strain energy (MSE) approach. This approach to damping design traditionally has involved a practitioner to vary placement and stiffness of add-on elements using experience and trial and error so as to maximize the add-on element share of system MSE in modes of interest. In this paper we develop a new technique for maximizing strain energy as a function of stiffness for add-on structural elements modeled as rank r perturbations to the original stiffness matrix. The technique is based on a constrained substructure approach allowing us to parameterize strain energy in terms of the eigenvalues of the perturbed structure. An optimality condition is derived that relates the input-output response at the attachment location of the add-on elements to the maximum achievable strain energy. A realizability condition is also derived which indicates whether or not the optimal solution is achievable with passive structural elements. This method has applications in the design of structural treatments for controlling sound and vibration and promises an efficient means of determining the limits of performance of passive structural treatments. An advantage of our approach over existing methods is that the maximum achievable strain energy fraction in the add-on elements is directly computable with the realizability condition then indicating whether the optimal solution is achievable.
Numerical Procedure for the Simulation of Wheel/Rail Contact Dynamics
Authors: Shabana Ahmed A. , Berzeri Marcello , Sany Jalil R.
Published: July 2002

In the multibody formulation of the contact problem, the kinematic contact constraint conditions are formulated in terms of the normal and tangents to the contact surfaces. Using the assumption of nonconformal contact, the second time derivatives of the contact constraints, which are required in the augmented Lagrangian formulation of the multibody equations, contain third derivatives of the position vectors of the contact points with respect to the surface parameters that describe the geometry of the contact surfaces. These derivatives must be accurately calculated in order to develop a robust numerical algorithm for solving the multibody differential and algebraic equations of the contact problem. An important application for the procedure developed in this paper is the wheel/rail interaction. In order to allow a general description for the wheel and rail profiles, the spline function representation is used. A multi-layer spline function algorithm is used in order to ensure accurate calculation of the third derivatives with respect to the surface parameters when a small number of nodal points is used. The problems of continuity of the derivatives and smoothness of these functions are addressed. The proposed method allows using wheel and rail profiles obtained from direct measurements. Numerical results show that this multibody approach, whic leads to accurate value of the normal force at the contact, can capture the coupling between the vertical and the lateral motion of the wheelset.
Corner-Filleted Flexure Hinges
Authors: Lobontiu Nicolae , Paine Jeffrey S. N. , Garcia Ephrahim , Goldfarb Michael
Published: July 2002

The paper presents an analytical approach to corner-filleted flexure hinges. Closed- form solutions are derived for the in-plane compliance factors. It is demonstrated that the corner-filleted flexure hinge spans a domain delimited by the simple beam and the right circular flexure hinge. A comparison that is made with the right circular flexure hinges indicates that the corner-filleted flexures are more bending-compliant and induce lower stresses but are less precise in rotation. The finite element simulation and experimental results confirmed the model predictions.
A High-Temperature Catalytic Combustor With Starting Burner
Authors: Yoshida Y. , Oyakawa K. , Aizawa Y. , Kaya H.
Published: July 2002

A catalytic combustion system has high potential to achieve low NOx emission level. When this combustion system is applied to a gas turbine, the required combustor performance must be maintained over a wide range of operating conditions. These conditions range from cold starting to steady-state operation. Particularly during the initial stage of cold starting when the catalyst is not yet activated, the catalyst must be heated by some means. This study proposes a new concept of a catalytic combustor with a direct heating system using vaporizing tube for starting burner in order to downsize the combustor and reduce the warm-up time during cold starts. The effectiveness of this concept is experimentally verified. Furthermore, NOx, CO, and HC emissions during startup can be reduced to a low level so as to achieve ultra-low pollution of the catalytic combustion over a wide range of operating conditions from cold start to steady-state operation. This paper outlines the operation concept covering cold start, verification of the concept through the experiments with flame visualization in the combustor, spray characteristics, construction of the combustor, and combustion characteristics that show low pollution in various operating conditions of the catalytic combustor.
Technical Basis for ASME Section VIII Code Case 2235 on Ultrasonic Examination of Welds in Lieu of Radiography
Authors: Rana Mahendra D. , Hedden Owen , Cowfer Dave , Boyce Roger
Published: July 2002

In 1996, Code Case 2235, which allows ultrasonic examination of welds in lieu of radiography for ASME Section VIII Division 1 and Division 2 vessels, was approved by the ASME B&PV Code Committee. This Code Case has been revised to incorporate: 1) a reduction in minimum usable thickness from 4″ (107.6 mm) to 0.5″ (12.7 mm), and 2) flaw acceptance criteria including rules on multiple flaws. A linear elastic fracture mechanics procedure has been used in developing the flaw acceptance criteria. This paper presents the technical basis for Code Case 2235.
Air Gap Response of Floating Structures: Statistical Predictions Versus Observed Behavior
Authors: Winterstein Steven R. , Sweetman Bert
Published: July 2002

The air gap response of a specific semi-submersible platform subjected to irregular waves is considered. Detailed model tests for this structure are studied in depth. Using time-histories of both motions and air gap, statistical analyses both for the absolute near-structure wave elevation (with respect to a fixed observer), and the relative wave elevation (with respect to the moving structure) are performed. Statistics of wave crest amplification, due to diffraction, are established. Corresponding amplification factors are derived from linear diffraction theory, and the results of theory and observations are critically compared.
Evaluation of Prestraining and Dynamic Loading Effects on the Fracture Toughness of Structural Steels by the Local Approach
Authors: Minami Fumiyoshi , Arimochi Kazushige
Published: July 2002

On the occasion of recent great earthquakes, great concern is focused on the prevention of unstable fracture of steel structures against the seismic loading. This paper employs the local approach for the evaluation of prestraining and dynamic loading effects, experienced during an earthquake, on the fracture toughness of structural steels. The prestraining and dynamic loading lead to a similar result: increasing the yield stress and tensile strength and decreasing the fracture toughness. It is shown, however, that the combined effects of prestraining and dynamic loading is not equivalent to the sum of each individual effect. The analysis using the local approach demonstrates that the critical Weibull stress at brittle fracture initiation is independent of prestraining and dynamic loading. Based on the Weibull stress fracture criterion, the prestraining and dynamic loading effects on the fracture toughness can be predicted from static toughness results of the virgin material. As an engineering application, a simplified method is proposed for the estimation of fracture toughness under the seismic condition. This method uses a reference temperature concept: the dynamic fracture toughness at the service temperature T with prestrain is displaced by the static toughness of the virgin material at a lower temperature T−ΔTPD, where ΔTPD is a temperature shift of the fracture toughness caused by prestraining and dynamic loading. The temperature shift ΔTPD is provided as a function of the flow stress elevation in the seismic condition.
Asymptotic Solutions of Penny-Shaped Inhomogeneities in Global Eshelby’s Tensor
Authors: Yang Q. , Zhou W. Y. , Swoboda G.
Published: July 2002

In this paper, a three-dimensional penny-shaped isotropic inhomogeneity surrounded by unbounded isotropic matrix in a uniform stress field is studied based on Eshelby’s equivalent inclusion method. The solution including the deduced equivalent eigenstrain and its asymptotic expressions is presented in tensorial form. The so-called energy-based equivalent inclusion method is introduced to remove the singularities of the size and eigenstrain of the Eshelby’s equivalent inclusion of the penny-shaped inhomogeneity, and yield the same energy disturbance. The size of the energy-based equivalent inclusion can be used as a generic damage measurement.
A Knowledge-Based Tuning Method for Injection Molding Machines
Authors: Yang Dongzhe , Danai Kourosh , Kazmer David
Published: July 2002

Complexity of manufacturing processes has hindered methodical specification of machine setpoints for improving productivity. Traditionally in injection molding, the machine setpoints are assigned either by trial and error, based on heuristic knowledge of an experienced operator, or according to an empirical model between the inputs and part quality attributes, which is obtained from statistical design of experiments (DOE). In this paper, a Knowledge-Based Tuning (KBT) Method is presented which takes advantage of the a priori knowledge of the process, in the form of a qualitative model, to reduce the demand for experimentation. The KBT Method provides an estimate of the process feasible region (process window) as the basis of finding the suitable setpoints, and updates its knowledge-base using the data that become available during tuning. As such, the KBT Method has several advantages over conventional tuning methods: (1) the qualitative model provides a generic form of representation for linear and nonlinear processes alike, therefore, there is no need for selecting the form of the empirical model through trial and error, (2) the use of a priori knowledge eliminates the need for initial trials to construct an empirical model, so an initial feasible region can be identified as the basis of search for the suitable setpoints, and (3) the search within the feasible region leads to a higher fidelity model of this region when the input/output data from consecutive process iterations are used for learning. The KBT Method’s utility is demonstrated in production of digital video disks (DVDs).
High-Resolution Measurements of Local Heat Transfer Coefficients From Discrete Hole Film Cooling
Authors: Baldauf S. , Schulz A. , Wittig S.
Published: July 2002

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied over a wide range, emphasizing engine relevant conditions. A high-resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained from a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled test plate measured with thermocouples were applied as boundary conditions in this heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hf based on the difference between actual wall temperatures and adiabatic wall temperatures in the presence of film cooling. The hf data are given for an engine relevant density ratio of 1.8. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results for identical flow situations (i.e., constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf are recognized and quantified as the different ejection parameters are changed. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD codes in discrete hole film cooling.
A Cause of Cracking in the Under-Bump-Metallurgy Area of Flip Chips
Authors: Mirman Boris , Bobrov Emanuel
Published: July 2002

Plastic compressive deformation of the copper layer at high temperatures is a significant contributor for die cracking in the under-bump-metallurgy (UBM) area of flip chips.
Microstructural Randomness Versus Representative Volume Element in Thermomechanics
Authors: Ostoja-Starzewski M.
Published: July 2002

Continuum thermomechanics hinges on the concept of a representative volume element (RVE), which is well defined in two situations only: (i) unit cell in a periodic microstructure, and (ii) statistically representative volume containing a very large (mathematically infinite) set of microscale elements (e.g., grains). Response of finite domains of material, however, displays statistical scatter and is dependent on the scale and boundary conditions. In order to accomplish stochastic homogenization of material response, scale-dependent hierarchies of bounds are extended to dissipative/irreversible phenomena within the framework of thermomechanics with internal variables. In particular, the free-energy function and the dissipation function become stochastic functionals whose scatter tends to decrease to zero as the material volume is increased. These functionals are linked to their duals via Legendre transforms either in the spaces of ensemble average velocities or ensemble-average dissipative forces. In the limit of infinite volumes (RVE limit (ii) above) all the functionals become deterministic, and classical Legendre transforms of deterministic thermomechanics hold. As an application, stochastic continuum damage mechanics of elastic-brittle solids is developed.
Damage Detection Using Expanded Dynamic Residuals
Authors: Zimmerman David C. , Kim Hyoung M. , Bartkowicz Theodore J. , Kaouk Mohamed
Published: July 2002

In this work, an algorithm for detecting the location of damage in a structure using a finite element model and pre- and post-damage measured modal properties is presented. In particular, an algorithm which addresses one aspect of the incomplete measurement problem, namely the measurement of mode shape information at fewer spatial degrees of freedom than that modeled in the finite element model, is presented. The performance of the algorithm is evaluated using the NASA 8-bay experimental test bed. The results indicate that the proposed approach holds great promise for identifying damage when structural instrumentation is limited. The same approach can also be used in model correlation efforts to aid in the selection of physical parameters to be estimated.
Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part I: Three-Dimensional Vortical Flow Structures
Authors: Jang Choon-Man , Furukawa Masato , Inoue Masahiro
Published: July 2002

Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade tip suction side near the midchord. Even at the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.
Viscosity Effects on the Propagation of Acoustic Transients
Authors: Gaunaurd G. C. , Everstine G. C.
Published: July 2002

The propagation of an impulsive excitation applied at the origin of a lossy viscous medium is studied by operational techniques as the excitation advances through the medium. The solution of the governing partial differential equation (PDE) for such transient propagation problems has been elusive. Such solution is found as an infinite sum of properly weighted successive integrals of the complementary error function, and it is quantitatively examined here using a one-dimensional model in space and time. As expected, as the transient advances through space, its amplitude decreases, and its width broadens. Such is the damping effect of viscosity that one would anticipate from elementary considerations in related disciplines such as electrodynamics. Such is also the smoothing-out effect of dispersion. We also obtain an approximate solution of the present boundary-initial value problem based on the method of steepest descents. This approximation agrees with the first term of the complete analytic solution given here. The pertinent dispersion relation associated with the governing parabolic PDE is shown to impose a restrictive condition on the allowable values of the propagation speed and the kinematic viscosity coefficient, thus assuring that propagation with attenuation does take place. Various numerical results illustrate and quantitatively describe the propagation of the transient pulse in several nondimensional graphs.
Effective Radiative Properties of a Cylinder Array
Authors: Zhang Chongshan , Kribus Abraham , Ben-Zvi Rami
Published: July 2002

Fully anisotropic problems are found where the radiative interaction is due to small-scale elements that lack spherical symmetry, for example: fibrous insulation, finned heat sinks, plant canopies, and some solar energy absorbers. We present the effective bulk optical properties of a PM composed of small-scale opaque cylinders. The properties are derived from data generated by detailed Monte-Carlo numerical experiments. The data reduction procedure is relatively simple and does not require a full solution and optimization of the Radiative Transfer Equation. Benchmark cases are presented, comparing an exact solution (with geometric detail of the cylinder array) and an approximate solution using a continuous PM model with the effective volumetric properties.
Use of Topological Constraints in Construction and Processing of Robust Solid Models
Authors: Higashi Masatake , Nakano Hisashi , Nakamura Atsuhide , Hosaka Mamoru
Published: July 2002

This paper introduces topological constraints to robustly and comprehensively process interference calculation in solid modeling and feature modeling, and describes a method of symbolic notation of their expressions and algorithms to handle them. The interference calculation should be processed consistently against the contradictions in numerical values and should output the result model in the same form of representation as that in the input. To satisfy this, the topological constraints are relied on in the processing rather than numerical values, and represented symbolically and explicitly in the solid model, which is based on the Face-based representation using a table of sequences of face names around each face of the solid. The topological constraints represent degeneracy and connectedness among faces, edges and vertices, and are used against errors derived from the ambiguities caused in the numerical calculation as well as in the input data, while the errors are deliberately kept within a given tolerance. The constraints are also specified by a designer for representing his intention. When the intersection is regarded as degenerate at a point such as vertex-vertex coincidence, its topological constraint is represented by a cluster of multiple basic intersection points between edges and faces, and the name of the cluster is expressed with face names around the degenerate point. In the calculation for the set operation, the symbols of cluster names and non-cluster intersection points are used to make intersection line loops, to divide the faces of both solids along the intersection lines and to reconnect the divided ones to make the result solid. Examples are shown to demonstrate that the algorithms generate output solids even when they are subtly intersected.
Adherence of a Rectangular Flat Punch Onto a Clamped Plate: Transition From a Rigid Plate to a Flexible Membrane
Authors: Wan K.-T. , Duan J.
Published: July 2002

A linear elastic solution is proposed for the adhesion/delamination of a constrained thin film adhered to a rectangular flat punch. As the punch is pulled away by an external load, the film deforms and gradually delaminates until a line contact is left prior to complete separation. This is in sharp contrast with the finite pull-off contact radius as predicted by the classical Johnson-Kendall-Roberts theory for adhesion between solid bodies. In order to portray the transition from a platelike to a membranelike behavior, the film thickness and stiffness are allowed to span a wide range of values. Simple experiments demonstrated the validity of the theory.
Approach for Input Uncertainty Propagation and Robust Design in CFD Using Sensitivity Derivatives1
Authors: Putko Michele M. , Taylor , Arthur C. , Newman Perry A. , Green Lawrence L.
Published: July 2002

An implementation of the approximate statistical moment method for uncertainty propagation and robust optimization for quasi 1-D Euler CFD code is presented. Given uncertainties in statistically independent, random, normally distributed input variables, first-and second-order statistical moment procedures are performed to approximate the uncertainty in the CFD output. Efficient calculation of both first- and second-order sensitivity derivatives is required. In order to assess the validity of the approximations, these moments are compared with statistical moments generated through Monte Carlo simulations. The uncertainties in the CFD input variables are also incorporated into a robust optimization procedure. For this optimization, statistical moments involving first-order sensitivity derivatives appear in the objective function and system constraints. Second-order sensitivity derivatives are used in a gradient-based search to successfully execute a robust optimization. The approximate methods used throughout the analyses are found to be valid when considering robustness about input parameter mean values.
Heat Transfer and Phase Transformations in Laser Annealing of Thin Si Films
Authors: Moon Seung-Jae , Lee Minghong , Grigoropoulos Costas P.
Published: July 2002

Recrystallization of thin amorphous silicon (a-Si) films can yield polysilicon (p-Si) material with functional properties suitable for fabrication of electronic devices, including high definition large area active matrix liquid crystal displays. Pulsed laser-effected melting and recrystallization is exceptionally effective since it avoids damage to the underlying insulator structure. The ensuing phase transformations and ultimately the quality of the produced p-Si material strongly depend on the temperature history. This article presents a review of research aiming to understand the complex nucleation, resolidification and crystal growth phenomena that evolve under severely non-equilibrium conditions. It is shown that elucidation of the fundamental thermodynamic processes enables conception of novel practical thin film crystal growth techniques.
A Numerical Scheme for Dynamic Systems Containing Fractional
Derivatives
Authors: Yuan Lixia , Agrawal Om P.
Published: July 2002

This paper presents a numerical scheme for dynamic analysis of mechanical systems subjected to damping forces that are proportional to fractional derivatives of displacements. These equations appear in the modeling of frequency dependent viscoelastic damping of materials. In the scheme presented, the fractional differential equation governing the dynamics of a system is transformed into a set of differential equations with no fractional derivative terms. Using Laguerre integral formula, this set is converted to a set of first order ordinary differential equations, which are integrated using a numerical scheme to obtain the response of the system. In contrast to other numerical techniques, this method does not require one to store the past history of the response. Numerical studies show that the solution converges as the number of Laguerre node points increase. Further, results obtained using this scheme agree well with those obtained using analytical techniques.
Microstructure-Level Modeling of Ductile Iron Machining
Authors: Chuzhoy L. , DeVor R. E. , Kapoor S. G. , Bammann D. J.
Published: July 2002

A microstructure-level model for simulation of machining of cast irons using the finite element method is presented. The model explicitly combines ferritic and pearlitic grains with graphite nodules to produce the ductile iron structure. The behaviors of pearlite, ferrite, and graphite are captured individually using an internal state variable model for the material model. The behavior of each phase is dependent on strain, strain rate, temperature, and amount of damage. Extensive experimentation was conducted to characterize material strain rate and temperature dependency of both ferrite and pearlite. The model is applied to orthogonal machining of ductile iron. The simulation results demonstrate the feasibility of successfully capturing the influence of microstructure on machinability and part performance. The stress, strain, temperature, and damage results obtained from the model are found to correlate well with experimental results found in the literature. Furthermore, the model is capable of handling various microstructures in other heterogeneous materials such as steels.
Aeroelasticity Analysis of Air-Riding Seals for Aero-Engine Applications
Authors: Sayma A. I. , Bre´ard C. , Vahdati M. , Imregun M.
Published: July 2002

This paper presents the results of a feasibility study on air-riding seal aeroelasticity for large-diameter aero-engines. A literature survey of previous seal studies revealed a significant amount of experimental work but numerical modeling using CFD techniques was relatively scarce. Indeed, most existing theoretical studies either deal with the structural behavior, or use simplified flow modeling. The aeroelasticity stability of a simplified air-riding seal geometry, devised for this particular feasibility study, was analyzed in three dimensions for typical engine operating conditions. Both the unsteady flow and structural vibration aspects were considered in the investigation. The boundary conditions and the seal gap were varied to explore the capabilities and limitations of a state-of-the-art unsteady flow and aeroelasticity code. The methodology was based on integrating the fluid and structural domains in a time-accurate fashion by exchanging boundary condition information at each time step. The predicted characteristics, namely lift and flow leakage as a function of pressure and seal gap, were found to be in agreement with the expected behavior. Operating seal gaps were determined from the actual time histories of the seal motion under the effect of the aerodynamic and the restoring spring forces. Both stable and unstable cases were considered. It was concluded that, in principle, the existing numerical tools could be used for the flow and aeroelasticity analyses of hydrostatic seals. However, due to large Mach number variations, the solution convergence rate was relatively slow and it was recognized that a preconditioner was needed to handle seal flows. For small gaps of about 10 microns, typical of spiral groved seals, the flow has a high Knudsen number, indicating that the Navier-Stokes formulations may no longer be valid. Such cases require a totally different treatment for the modeling of steady and unsteady aerodynamics, either by modifying the transport parameters of the Navier-Stokes equations or by considering rarefied gas dynamics.
Study on Thin Film Lubrication With Second-Order Fluid
Authors: Huang Ping , Li Zhi-heng , Meng Yong-gang , Wen Shi-zhu
Published: July 2002

The basic lubrication equations are deduced from the original second-order fluid constitutive equations. Two examples of lubrication, a plane inclined slider and a journal bearing, are calculated respectively. The Reynolds boundary conditions are used in the calculation of the journal bearing. In this calculation, it is found that the load carrying capacities of the slider and the journal bearing are of different tendencies with the increase of the Deborah number. Furthermore, the results show that with the decrease of the film thickness, the increase of the normal stress of second-order fluid is greater than that of Newtonian fluid. Finally, it is found that the distribution of the normal stress changes significantly at a certain thickness.
Performance Evaluation of Coriolis Mass Flowmeters
Authors: Al-Khamis Mohammed N. , Al-Nojaim Ali A. , Al-Marhoun Muhammad A.
Published: July 2002

The first practical coriolis mass flowmeter was introduced in 1977. Today, there are several manufacturers which offer various coriolis mass flowmeters with different sensing tube configurations and geometry. These meters continue to evolve, gain wide acceptance, and are used in the chemical, petroleum, food and beverage industries because of the several features that they posses over other types of flow measurement devices. This paper presents a performance evaluation of three types of coriolis mass flowmeters: U-tube, modified U-tube, and straight tube meters. These meters were individually tested in a compact multiphase test unit (WellComp) located in an onshore area of a field in Saudi Arabia. The test results obtained from these meters were compared with simultaneous data obtained from turbine meters installed in a conventional test separator.
Design of Continuous Time Controllers Having Almost Minimum Time Response
Authors: Kalyon M.
Published: July 2002

A class of near time-optimal nonlinear controllers—the Continuous Proximate Time-Optimal (CPTO) controllers—which involves continuous, rather than discontinuous, nonlinear feedback control functions is introduced. The CPTO controllers give near time-optimal response for large state errors, and provide smooth, stable response with near linear control for small state errors. In this paper, the CPTO controllers for three second-order (two stable and one unstable) plants and one third-order plant are introduced. Complete stability proofs, using the CPTO control law, are given for all the systems considered. It has been shown through the simulation that response times are indeed near time-optimal for all cases considered.
Radiation of Body Waves Induced by the Sliding of an Elastic Half-Space Against a Rigid Surface
Authors: Adams G. G.
Published: July 2002

The steady sliding of a flat half-space against a rigid surface with a constant interfacial coefficient of friction is investigated. It is shown here that steady sliding is compatible with the formation of a pair of body waves (a plane dilatational wave and a plane shear wave) radiated from the sliding interface. Each wave propagates at a different angle such that the trace velocities along the interface are equal and supersonic with respect to the elastic medium. The angles of wave propagation are determined by the Poisson’s ratio and by the coefficient of friction. The amplitude of the waves are indeterminant, subject only to the restriction that the perturbations in interface contact pressure and tangential velocity satisfy the inequality constraints for unilateral sliding contact. It is also found that a rectangular wave train, or a rectangular pulse, can allow for motion of the two bodies with a ratio of remote shear to normal stress which is less than the coefficient of friction. Thus the apparent coefficient of friction is less than the interface coefficient of friction. Furthermore it is shown that the apparent friction coefficient decreases with increasing speed even if the interface friction coefficient is speed-independent. This result supports the interpretation of certain friction behavior as being a consequence of the dynamics of the system, rather than strictly as an interface property. In fact no distinction is made between the static and kinetic interface friction coefficients. [S0021-8936(00)02101-2]
Unconfined Compression of Articular Cartilage: Nonlinear Behavior and Comparison With a Fibril-Reinforced Biphasic Model
Authors: Fortin M. , Soulhat J. , Shirazi-Adl A. , Hunziker E. B. , Buschmann M. D.
Published: July 2002

Mechanical behavior of articular cartilage was characterized in unconfined compression to delineate regimes of linear and nonlinear behavior, to investigate the ability of a fibril-reinforced biphasic model to describe measurements, and to test the prediction of biphasic and poroelastic models that tissue dimensions alter tissue stiffness through a specific scaling law for time and frequency. Disks of full-thickness adult articular cartilage from bovine humeral heads were subjected to successive applications of small-amplitude ramp compressions cumulating to a 10 percent compression offset where a series of sinusoidal and ramp compression and ramp release displacements were superposed. We found all equilibrium behavior (up to 10 percent axial compression offset) to be linear, while most nonequilibrium behavior was nonlinear, with the exception of small-amplitude ramp compressions applied from the same compression offset. Observed nonlinear behavior included compression-offset-dependent stiffening of the transient response to ramp compression, nonlinear maintenance of compressive stress during release from a prescribed offset, and a nonlinear reduction in dynamic stiffness with increasing amplitudes of sinusoidal compression. The fibril-reinforced biphasic model was able to describe stress relaxation response to ramp compression, including the high ratio of peak to equilibrium load. However, compression offset-dependent stiffening appeared to suggest strain-dependent parameters involving strain-dependent fibril network stiffness and strain-dependent hydraulic permeability. Finally, testing of disks of different diameters and rescaling of the frequency according to the rule prescribed by current biphasic and poroelastic models (rescaling with respect to the sample’s radius squared) reasonably confirmed the validity of that scaling rule. The overall results of this study support several aspects of current theoretical models of articular cartilage mechanical behavior, motivate further experimental characterization, and suggest the inclusion of specific nonlinear behaviors to models. [S0148-0731(00)00702-0]
Viscoelastic Behavior of a Lung Alveolar Duct Model
Authors: Denny E. , Schroter R. C.
Published: July 2002

A study is conducted into the oscillatory behavior of a finite element model of an alveolar duct. Its load-bearing components consist of a network of elastin and collagen fibers and surface tension acting over the air–liquid interfaces. The tissue is simulated using a visco-elastic model involving nonlinear quasi-static stress–strain behavior combined with a reduced relaxation function. The surface tension force is simulated with a time- and area-dependent model of surfactant behavior. The model was used to simulate lung parenchyma under three surface tension cases: air-filled, liquid-filled, and lavaged with 3-dimethyl siloxane, which has a constant surface tension of 16 dyn/cm. The dynamic elastance Edyn and tissue resistance Rti were computed for sinusoidal tidal volume oscillations over a range of frequencies from 0.16–2.0 Hz. A comparison of the variation of Edyn and Rti with frequency between the model and published experimental data showed good qualitative agreement. Little difference was found in the model between Rti for the air-filled and lavaged models; in contrast, published data revealed a significantly higher value of Rti in the lavaged lung. The absence of a significant increase in Rti for the lavaged model can be attributed to only minor changes in the individual fiber bundle resistances with changes in their configuration. The surface tension was found to make an important contribution to both Edyn and Rti in the air-filled duct model. It was also found to amplify any existing tissue dissipative properties, despite exhibiting none itself over the small tidal volume cycles examined. [S0148-0731(00)00502-1]
Toward Improved Rotor-Only Axial Fans—Part II: Design Optimization for Maximum Efficiency
Authors: So̸rensen D. N. , Thompson M. C. , So̸rensen J. N.
Published: July 2002

Numerical design optimization of the aerodynamic performance of axial fans is carried out, maximizing the efficiency in a design interval of flow rates. Tip radius, number of blades, and angular velocity of the rotor are fixed, whereas the hub radius and spanwise distributions of chord length, stagger angle, and camber angle are varied to find the optimum rotor geometry. Constraints ensure a pressure rise above a specified target and an angle of attack on the blades below stall. The optimization scheme is used to investigate the dependence of maximum efficiency on the width of the design interval and on the hub radius. [S0098-2202(00)01602-3]
Modeling of Conjugate Two-Phase Heat Transfer During Depressurization of Pipelines
Authors: Fairuzov Y. V.
Published: July 2002

Transient conjugate two-phase heat transfer during depressurization of pipelines containing flashing liquids is examined in this paper. A numerical model for transient flashing liquid flow in a pipe is formulated. The model takes into account the transient radial heat conduction and the forced convection effects. Numerical simulation of flashing two-component (propane and butane) flow is performed in order to investigate the effect of wall friction on the heat transfer conditions in the pipe. The simulation results are compared with predictions of the model that are based on a new formulation of energy equation proposed by the author in an early study. A comparison of the results obtained allows one to determine the range of applicability of the new energy equation formulation. A procedure is proposed for choosing an appropriate model for predicting transient conjugate two-phase heat transfer during releases of flashing liquids from pipes. A criterion of thermodynamic similarity for flashing liquids flows in pipes or channels is formulated. The proposed criterion provides the basis for selecting model fluids and for constructing experimental models of systems containing flashing (volatile) liquids with scaled thermodynamic conditions. An example of its use is given. [S0022-1481(00)02001-6]
On the Enhancement of the Thermal Contact Conductance: Effect of
Loading History
Authors: Li Y. Z. , Madhusudana C. V. , Leonardi E.
Published: July 2002

A resistance to heat flow exists at the junction of two surfaces. It has long been recognized that there exists a hysteresis effect, that is, the value of thermal contact resistance in the unloading process is less than that in the loading process at the same load. However, little work has been done in utilizing this phenomenon to enhance the thermal contact conductance. The present experimental work investigated the effect of loading history; in particular the number of load cycles and overloading pressure, on the thermal contact conductance. It was found that the value of the thermal contact conductance might be enhanced by up to 51 percent. A cost-effective way of enhancing the contact conductance is suggested. [S0022-1481(00)01601-7]
Erratum: “Mixture Fraction Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes” [ASME J. Heat Transfer, 121, pp. 837–843 (1999)]
Authors: Sangras, R. , Dai, and Z. , Faeth G. M.
Published: July 2002

[S0022-1481(00)03102-9]
Accurate Modelling of Complex Functional Surfaces for Mechanical Design Using Freeform Surfaces
Authors: Lee Y. T. , Fang L.
Published: July 2002

Freeform curves and surfaces are commonly used in CAD, and NURBS is particularly popular because it can model freeform curves and surfaces as well as conic curves and quadric surfaces exactly. This paper describes a method that allows the creation of NURBS surfaces that approximate complex functional surfaces that can be described in closed form. The accuracy of the approximation can be controlled. [S1050-0472(00)00202-6]
New UHMWPE/Rubber Bearing Alloy
Authors: Orndorff, Roy L.
Published: July 2002

A new polymer bearing alloy has been developed that overcomes the high wear nonhydrodynamic deficiencies of UHMWPE when water-lubricated and the shaft wear and high breakaway friction of rubber bearings (Orndorff, Jr., R. L., 1988, “Thermoplastic-Rubber Polymer Alloys and Method for Producing the Same,” United States Patents, 4,725,151 and 4,735,982). Testing covered clean-water high-load and light-load highly abrasive wear testing as well as bearing friction testing. A number of competing materials were also wear tested with the new alloy comparing favorably. Shaft (drum) wear was determined to be zero on the abrasive test. The wear of the polymer alloy decreased by 70% when the high-load sample axial length was reduced by 50% to increase the contact pressure. Rubber bearing wear increased by almost ten times under the same condition. It is hypothesized that the higher-pressure clean-water test sample of the new alloy adjusted to run in the hydrodynamic regime through elastic deflection, creep and a minimal amount of wear. The breakaway coefficient of friction decreased by 67% compared with rubber bearings and the kinetic fiction decreased with increasing load as did the wear. The new alloy will allow water-lubricated rubber bearing length-to-diameter ratios to be reduced from the present value of four to one or less. Projected pressures can be increased five to ten times with the new alloy. [S0742-4787(00)04901-8]
Extending the Capability of the Greenwood Williamson Microcontact Model
Authors: McCool John I.
Published: July 2002

This paper describes a readily implemented simulation model that extends the Greenwood Williamson microcontact model to include skewness in the distribution of surface summit heights and the presence of a surface coating of prescribed thickness and compliance. Parametric runs were made to explore the effect of these factors on the load, area and mean real pressure at the contacting asperities for a fixed separation of the mean planes of the contacting surfaces such as occurs when the surfaces are separated by a stiff elastohydrodynamic film. It was found that the average asperity load increases with coating thickness when the coating is stiffer than the substrate and decreases when the coating is made more compliant. The opposite is true for the average asperity area of contact. Like load, the average asperity pressure increases with coating thickness when the coating is stiffer than the substrate and decreases when the coating is more compliant. For the same rms summit height the mean asperity pressure in the absence of a coating was found to be higher by a factor of 1.6 when the skewness is +1 than when it is −1. The relative effect of skewness on pressure is practically constant as coating thickness increases for the compliant coating while the absolute effect decreases. For the stiff coating the absolute effect is constant while the relative effect diminishes. [S0742-4787(00)02303-1]