bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Analysis of a Piezothermoelastic Resonator with Various Shapes
Authors: Fung Rong-Fong , Huang Jeng-Sheng , Jan Shang-Chin
Published: July 2002

The resonator is stimulated by piezoelectric ceramics to produce oscillations with frequencies in the ultrasonic region for the ultrasonic motor application. The steady-state temperature rise due to the heat generated by this actuation and its effects on the dynamic behavior of the resonator are investigated. The effect of three different geometry shapes of the resonator is also studied for the resonator design. The piezothermoelasticity theory is applied to model the complex coupled phenomenon of interaction among the mechanical deformation, electric field and temperature distribution. The extended Hamilton’s principle is used for formulation and the finite element method is used to approximate the governing equations for numerical simulation. It is found that the resonator expands axially due to this temperature rise and thus the trajectory of the resonator tip has an offset, which is large compared to the axially moving range of the tip trajectory. The shape of the resonator can change a little bit of the temperature distribution in the resonator, but it has large impact on the natural frequencies of the resonator. [S0739-3717(00)01003-5]
A Variational Boundary Integral Method for the Analysis of Three-Dimensional Cracks of Arbitrary Geometry in Anisotropic Elastic Solids
Authors: Xu G.
Published: July 2002

A variational boundary integral method is developed for the analysis of three-dimensional cracks of arbitrary geometry in general anisotropic elastic solids. The crack is modeled as a continuous distribution of dislocation loops. The elastic energy of the solid is obtained from the known expression of the interaction energy of a pair of dislocation loops. The crack-opening displacements, which are related to the geometry of loops and their Burgers vectors, are then determined by minimizing the corresponding potential energy of the solid. In contrast to previous methods, this approach results in the symmetric system of equations with milder singularities of the type 1/R, which facilitate their numerical treatment. By employing six-noded triangular elements and displacing midside nodes to quarter-point positions, the opening profile near the front is endowed with the accurate asymptotic behavior. This enables the direct computation of stress intensity factors from the opening displacements. The performance of the method is assessed by the analysis of an elliptical crack in the transversely isotropic solid. It also illustrates that the conventional average schemes of elastic constants furnish quite inaccurate results when the material is significantly anisotropic. [S0021-8936(00)02702-1]
Extended GLOSS Method for Determining Inelastic Effects in Mechanical Components and Structures: Isotropic Materials
Authors: Seshadri R. , Babu S.
Published: July 2002

The extended GLOSS method of analysis has been presented here that leads to conservative bounds on inelastic local strains. Consequently, the local region constraint parameter λ¯ is determined which can be used to evaluate multiaxial stress relaxation, creep damage, low-cycle fatigue, and elastic-plastic fracture. The method is used to determine inelastic local strains for several component configurations, subjected to mechanical as well as thermal loadings, and then compared with the corresponding inelastic FEA results. [S0094-9930(00)00404-2]
On the General Solutions for Annular Problems With a Point Heat Source
Authors: Chao C. K. , Tan C. J.
Published: July 2002

A general analytical solution for the annular problem with a point heat source is provided in this paper. Based upon the method of analytical continuation and the technique of Fourier series expansions, the series solutions of the temperature and stress functions are expressed in complex explicit form. Single-valuedness of complex functions in the doubly connected region has been examined for both the stress-free and displacement-free boundary conditions. The dilatation stress in the annulus due to the application of a point heat source is discussed and shown in graphic form. [S0021-8936(00)02803-8]
Influence of Vane/Blade Spacing on the Heat Flux for a Transonic Turbine
Authors: Dunn M. G. , Haldeman C. W. , Abhari R. S. , McMillan M. L.
Published: July 2002

An experimental and analytical research program determining the influence of vane/blade spacing on the vane and blade time-averaged and unsteady heat flux for a full-scale rotating turbine stage was performed. The turbine stage was operated at a transonic vane exit condition, with pressure and heat flux measurements obtained throughout the stage. This paper focuses on the midspan heat flux measurements for both the vane and blade at three vane/blade axial spacings: 20, 40, and 60 percent of vane axial chord. The time-averaged heat flux results for the vane and the blade are compared with predictions obtained using a two-dimensional, Reynolds-averaged multiblade row code, UNSFLO, developed by Giles (1984). The measured and predicted unsteady heat flux envelopes (as a function of vane/blade spacing) are also compared with predictions. For selected locations on the blade, a direct comparison between the measured phase-averaged surface pressure and the measured phase-averaged Nusselt number history is presented. At some locations along the surface the pressure and the heat flux are shown to be in phase, but at other locations they are not. The influence of vane/blade spacing on the blade heat load was found to be small, and much less than the differences caused by changes in the Reynolds number during the experimental matrix. [S0889-504X(00)00904-1]
A Unifying Characterization of Robust Sliding Mode Control: A Lyapunov Approach
Authors: DeCarlo R. A. , Drakunov S. V. , Li Xiaoqiu
Published: July 2002

This paper sets forth general conditions on the existence, boundedness, and proper gains of a control for stabilizing a nonlinear plant state trajectory to a sliding manifold denoted by S contained in the state space as characterized by a smooth quadratic Lyapunov function, V. To state such conditions we define a time-varying (possibly discontinuous in time) state-dependent decision manifold by considering the time-derivative of the quadratic Lyapunov function. The decision manifold disconnects the control space. At each instant of time, stability is achieved by choosing a control in an appropriate half space defined by the decision manifold so that the derivative of the Lyapunov function is negative definite. If the decision manifold moves continuously, then there is no need for a discontinuous (classical VSC) controller unless robustness in the presence of matched disturbances is desired. If the decision manifold is discontinuous, then the need for a discontinuous control is clear. The formulation unifies the various VSC control strategies found in the literature under a single umbrella and suggests new structures. The formulation also provides a simple geometric understanding of the effect of norm bounded but not necessarily matched disturbances and parameter variations on the system. Two examples illustrate the design aspects of the formulation. [S0022-0434(00)02904-X]
Modified Lagrange Method to Analyze Problems of Sliding and Rolling
Authors: Rosen A.
Published: July 2002

A modified Lagrange method to analyze problems of sliding and rolling is presented. The method is based on modeling the friction as a process of collisions between the sliding and rolling body, and particles of the surface on which it slips and rolls. The process of collisions does not need to describe the exact friction process. Instead it can represent another equivalent mechanism of loss of energy of the body due to sliding and rolling. The function that describes the rate of increase of the kinetic energy of the particles, as a result of the collisions, plays a major roll in the modified Lagrange equations. Cases of isotropic and anisotropic friction can be modeled. Three examples of using the method are presented. It is shown that when an infinitely rough surface is assumed, the classical equations for nonholonomic constraints of rolling without sliding are obtained. Lagrange multipliers that appear in these equations obtain direct physical meaning and the mechanism behind the constraint becomes clear. [S0021-8936(00)01404-5]
The Effect of Magnetic Field on Local Heat Transfer Coefficient in Fluidized Beds With Immersed Heating Surface
Authors: Al-Qodah Z. , Al-Busoul M.
Published: July 2002

Five different magnetic particles have been used to investigate the effect of a transverse magnetic field on the thermal behavior of a gas fluidized bed, with an immersed heating spherical surface. The effects of gas superficial velocity and magnetic field intensity on the behavior of the temperature distribution and the local heat transfer coefficient at different radial and axial positions in the bed was investigated. In the present study a correlation relating Nusselt number to the magnetic field intensity is proposed.
Estimation of Thermophysical Properties by the Spectral Method—Development and Evaluation
Authors: Aviles-Ramos C. , Haji-Sheikh A. , Beck J. V. , Dowding K. J.
Published: July 2002

This paper reports the evaluation of a spectral technique for estimating thermophysical properties. It demonstrates that one can construct a virtual quasi-steady periodic experiment from a limited but properly selected set of transient non-periodic data. In the spectral domain, the phase angles of the responses at different locations relative to a periodic input signal depend on the thermophysical properties. For the purpose of this evaluation, the transient temperature responses to a surface heat flux input are analytically obtained at pre-selected sensor locations. The transient data are converted to periodic data, phase angles are computed, and thermophysical properties are estimated. All deviations from known property values due to numerical errors are reported.
On Two-Dimensional Laminar Hydromagnetic Fluid-Particle Flow Over a Surface in the Presence of a Gravity Field
Authors: Chamkha Ali J.
Published: July 2002

A continuum two-phase fluid-particle model accounting for particle-phase stresses and a body force due to the presence of a magnetic field is developed and applied to the problem of two-dimensional laminar hydromagnetic flow of a particulate suspension over a horizontal surface in the presence of a gravity field. Analytical solutions for the velocity distributions and the skin-friction coefficients of both phases are reported. Two cases of wall hydrodynamic (velocity) conditions corresponding to stationary and oscillatory velocity distributions are considered. Numerical evaluations of the analytical solutions are performed and the results are reported graphically to elucidate special features of the solutions. The effects of the particle-phase stresses and the magnetic field are illustrated through representative results for the horizontal velocity profiles, fluid-phase displacement thickness, and the complete skin-friction coefficient for various combinations of the physical parameters. It is found that the presence of the magnetic field increases the fluid-phase skin-friction coefficient for various particulate volume fraction levels while the presence of the particle-phase viscous stresses reduces it for various particle-to-fluid density ratios.
The Impact of Viscous Effects on the Aerodynamic Damping of Vibrating Transonic Compressor Blades—A Numerical Study
Authors: Gru¨ber Bjo¨rn , Carstens Volker
Published: July 2002

A parametric study which investigates the influence of viscous effects on the damping behavior of vibrating compressor cascades is presented here. To demonstrate the dependence of unsteady aerodynamic forces on the flow viscosity, a computational study was performed for a transonic compressor cascade of which the blades underwent tuned pitching oscillations while the flow conditions extended from fully subsonic to highly transonic flow. Additionally, the reduced frequency and Reynolds number were varied. In order to check the linear behavior of the aerodynamic forces, all calculations were carried out for three different oscillation amplitudes. Comparisons with inviscid Euler results helped identify the influence of viscous effects. The computations were performed with a Navier-Stokes code, the basic features of which are the use of an AUSM upwind scheme, an implicit time integration, and the implementation of the Baldwin-Lomax turbulence model. In order to demonstrate the possibility of this code to correctly predict the unsteady behavior of strong shock-boundary layer interactions, the experiment of Yamamoto and Tanida on a self-induced shock oscillation due to shock-boundary layer interaction was calculated. A significant improvement in the prediction of the shock amplitude was achieved by a slight modification of the Baldwin Lomax turbulence model. An important result of the presented compressor cascade investigations is that viscous effects may cause a significant change in the aerodynamic damping. This behavior is demonstrated by two cases in which an Euler calculation predicts a damped oscillation whereas a Navier-Stokes computation leads to an excited vibration. It was found that the reason for these contrary results are shock-boundary-layer interactions which dramatically change the aerodynamic damping.
Simulations of Crack Propagation in Porous Materials
Authors: Nakamura T. , Wang Z.
Published: July 2002

Failure propagation behavior of thermally sprayed coatings containing many random pores is investigated. The porous coatings are subjected to either external mechanical loads or residual stresses generated by temperature changes. The failure growth criterion is governed by the critical energy release rate. In our finite element analysis, the cohesive model is used to separate element boundaries during crack propagation in the inhomogeneous materials. The accuracy of the cohesive elements for the quasi-static crack growth is closely evaluated by an error analysis. We have observed that the cohesive elements may artificially increase the model compliance and introduce numerical errors. In order to minimize such errors, the parameters for cohesive model must be chosen carefully. Their numerical convergence and stability conditions with an implicit time integration scheme are also examined. In the porous material analysis, crack propagation is simulated to characterize its unique failure process. It appears a crack tends to propagate along the shortest path between neighboring pores. In addition, crack/pore coalescence mechanism causes the apparent crack length to increase discontinuously. Under thermally loaded conditions, the residual stresses generated by material mismatch in multilayered coatings drive cracks to grow. Using the present crack propagation model, the critical temperature leading to the complete porous coating failure can be approximated.
Mathematical Model for Large Deflection Dynamics of a Compliant Beam Device
Authors: Panza Michael J.
Published: July 2002

A mathematical model for the large deflection dynamics of a compliant beam device is presented. The device simulates the motion of a slider-crank device. The system contains a highly flexible beam that provides the compliant motion from a sliding mass at one end to a rotating hinge point at the other end. Basic models for friction and beam dissipation effects are included. A nonlinear integro-partial differential equation is derived for the complete beam/mass system in the curved space of the deformed beam. The resulting equation is cast into a generalized nondimensional form suitable for studying system behavior for a broad range of system sizes. The dynamic equation is solved in curved space by applying a spatial solution that closely represents the large static deflection measured for the beam. The nonlinear system dynamics are simulated for an initial large deflection of the system and compared to experimental results for an actual physical system.
A Unified Bifurcation Analysis of Sheet Metal Forming Limits
Authors: Zhu Xinhai , Weinmann Klaus , Chandra Abhijit
Published: July 2002

The purpose of this study is to determine analytically the orientations of localized necks occurring in sheet metal forming processes, and obtain the corresponding forming limit diagrams (FLDs). In addition to the force equilibrium condition as adopted by other researchers, we include the moment equilibrium in this study. The shear terms due to the perturbation are found to vanish inside the localized neck of a region of deformation. This simplifies the two-dimensional problem to a one-dimensional problem. Furthermore, it is found that there are only three possible orientations for the initiation of a localized neck, i.e., two principal directions and one zero extension direction (which applies only to negative strain ratio deformations). A special case study using the von Mises yield criterion is also presented in this paper. Predictions from our unified analysis matches with the results of Hill, R., 1952, “On Discontinuous Plastic States, With Special Reference to Localized Necking in Thin Sheets,” J. Mech. Phys. Solids, 1, pp. 19–30. For the negative strain ratio regime (left-hand side of the FLDs), and with the results of Storen, S., and Rice, R., 1975, “Localized Necking in Thin Sheets,” J. Mech. Phys. Solids, 23, pp. 421–441. For the positive strain ratio regime (right hand-side of the FLD). When the localized neck is assumed to be in the zero extension direction for the negative strain ratio deformation, deformation theory and flow theory of plasticity give the same limit strains, and a unified solution to the limit strain is obtained. This solution is independent of the specific yield criterion used.
Die Forging Stress Determination: A Dimensional Analysis Approach
Authors: Navarrete J. , Noguez M. E. , Ramı´rez J. , Salas G. , Robert T.
Published: July 2002

The stress provided by the forging press for manufacturing closed die forgings (forging stress) is evaluated through dimensional analysis. Five dimensionless groups, from the process variables, are proposed in order to simplify this forging stress determination. These groups are experimentally related. This relation is compared with the forging stresses of four industrial pieces with different shapes and alloys, reported in the literature. The results show that this methodology is useful for predicting the actual forging stress necessary in industrial closed die forgings.
Flow Dynamics and Heat Transfer of Wavy Condensate Film
Authors: Miyara Akio
Published: July 2002

Wave evolution and heat transfer behavior of a wavy condensate film down a vertical wall have been investigated by a finite difference method, in which the algorithm is based on the HSMAC method, and a staggered grid fixed on a physical space is employed. For the moving interface, newly proposed methods are used. A random perturbation of the film thickness is generated near the leading edge. The perturbation quickly diminishes once and small-amplitude long waves are propagated downstream. Then the amplitude of the wave increases rapidly at a certain position, and the wave shape changes from a sinusoidal wave to a pulse-like solitary wave which is composed of a large-amplitude wave and capillary waves. A circulation flow occurs in the large wave and it affects the temperature field. The heat transfer is enhanced by space-time film thickness variation and convection effects.
Characteristics of Creep Damage for 60 Sn-40 Pb Solder Material
Authors: Wei Y. , Chow C. L. , Fang H. E. , Neilsen M. K.
Published: July 2002

This paper presents a viscoplasticity model taking into account the effects of change in grain or phase size and damage on the characterization of creep damage in 60 Sn-40 Pb solder. Based on the theory of damage mechanics, a two-scalar damage model is developed for isotropic materials by introducing the free energy equivalence principle. The damage evolution equations are derived in terms of the damage energy release rates. In addition, a failure criterion is developed based on the postulation that a material element is said to have ruptured when the equivalent damage accumulated in the element reaches a critical value. The damage coupled viscoplasticity model is discretized and coded in a general-purpose finite element program known as ABAQUS through its user-defined material subroutine UMAT. To illustrate the application of the model, several example cases are introduced to analyze, both numerically and experimentally, the tensile creep behaviors of the material at three stress levels. The model is then applied to predict the deformation of a notched specimen under monotonic tension at room temperature (22°C). The results demonstrate that the proposed model can successfully predict the viscoplastic behavior of the solder material.
The Influence of Multiple Axial Erosions on the Fatigue Life of Autofrettaged Pressurized Cylinders
Authors: Perl M. , Levy C. , Ma Q.
Published: July 2002

Erosion geometry effects on the mode I stress intensity factor (SIF) for a crack emanating from an erosion’s deepest point in a multiply eroded, autofrettaged, pressurized, thick-walled cylinder are investigated. The problem is simulated as a two-dimensional problem and is solved via the finite element method. Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and SIFs are determined by the nodal displacement method. SIFs are evaluated for a variety of relative crack lengths, a0/t=0.01-0.45 emanating from the tip of erosions of different geometries, namely, (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t=0.05-0.4; and (c) semi-elliptical erosions with ellipticities of d/h=0.5-1.5, and erosion span angle, α, from 6 deg to 360 deg. The effective SIF for relatively short cracks is found to be increased by the presence of the erosion, which in turn may result in a significant decrease in the vessel’s fatigue life of up to an order of magnitude. Deep cracks are found to be almost unaffected by the erosion.
Stability of Precision Diamond Turning Processes That Use Round Nosed Tools*
Authors: Gilsinn D. E. , Davies M. A. , Balachandran B.
Published: July 2002

A system of retarded differential equations model is developed for a diamond-turning process with chip area cut by a round nosed tool. The results are presented in the form of stability charts that are found to be perturbed forms of those obtained for orthogonal cutting tools.
DQFEM Analyses of Static and Dynamic Nonlinear Elastic-Plastic Problems Using a GSR-Based Accelerated Constant Stiffness Equilibrium Iteration Technique
Authors: Chen Chang-New
Published: July 2002

An integrated numerical technique for static and dynamic nonlinear structural problems adopting the equilibrium iteration is proposed. The differential quadrature finite element method (DQFEM), which uses the differential quadrature (DQ) techniques to the finite element discretization, is used to analyze the static and dynamic nonlinear structural mechanics problems. Numerical time integration in conjunction with the use of equilibrium iteration is used to update the response history. The equilibrium iteration can be carried out by the accelerated iteration schemes. The global secant relaxation-based accelerated constant stiffness and diagonal stiffness-based predictor-corrector equilibrium iterations which are efficient and reliable are used for the numerical computations. Sample problems are analyzed. Numerical results demonstrate the algorithm.
Integrative Thermodynamic Optimization of the Crossflow Heat Exchanger for an Aircraft Environmental Control System
Authors: Vargas Jose V. C. , Bejan Adrian , Siems David L.
Published: July 2002

This paper documents the process of determining the internal geometric configuration of a component by optimizing the global performance of the installation that uses the component. The example chosen is the crossflow heat exchanger used in the environmental control system of a modern aircraft. The optimization of global performance is achieved by minimizing the total entropy generation rate of the installation. There are three degrees of freedom in the heat exchanger configuration (the length-to-width and height-to-width aspect ratios, and the separator plate spacing ratio), which is subjected to two global constraints: total component volume, and total wall material volume (or weight/density) of wall material. Numerical results show how the optimal configuration responds to changes in specified external parameters such as volume, weight, Mach number, diffuser inlet cross-sectional area, and the pressure at which the cabin air is initially bled from the engine compressor. It is shown that the optimal configuration is robust and that major features such as the ratios of channel spacings and flow lengths are relatively insensitive to changes in some of the external parameters. It is also shown that the optimal heat exchanger geometry is insensitive to the thermodynamic irreversibility caused by discharging the used ram air into the ambient.
Self-Excited Oscillations in Combustors With Spray Atomizers
Authors: Zhu M. , Dowling A. P. , Bray K. N. C.
Published: July 2002

Combustors with fuel-spray atomizers are susceptible to a low-frequency oscillation, particularly at idle and sub-idle conditions. For aero-engine combustors, the frequency of this oscillation is typically in the range 50–120 Hz and is commonly called “rumble.” In the current work, computational fluid dynamics (CFD) is used to simulate this self-excited oscillation. The combustion model uses Monte Carlo techniques to give simultaneous solutions of the Williams’ spray equation together with the equations of turbulent reactive flow. The unsteady combustion is calculated by the laminar flamelet presumed pdf method. A quasi-steady description of fuel atomizer behavior is used to couple the inlet flow in the combustor. A choking condition is employed at turbine inlet. The effects of the atomizer and the combustor geometry on the unsteady combustion are studied. The results show that, for some atomizers, with a strong dependence of mean droplet size on air velocity, the coupled system undergoes low-frequency oscillations. The numerical results are analyzed to provide insight into the rumble phenomena. Basically, pressure variations in the combustor alter the inlet air and fuel spray characteristics, thereby changing the rate of combustion. This in turn leads to local “hot spots,” which generate pressure fluctuations as they convect through the downstream nozzle.
Guided Waves in Thin-Walled Structural Members
Authors: Shah A. H. , Zhuang W. , Popplewell N. , Rogers J. B. C.
Published: July 2002

A semi-analytical finite element (SAFE) formulation is proposed to study the wave propagation characteristics of thin-walled members with an infinite length in the longitudinal (axial) direction. Common structural members are considered as an assemblage of thin plates. The ratio of the thickness of the plate to the wavelength in the axial direction is assumed to be small so that the plane-stress assumption is valid. Employing a finite element modeling in the transverse direction circumvents difficulties associated with the cross-sectional profile of the member. The dynamic behavior is approximated by dividing the plates into several line (one-dimensional) segments and representing the generalized displacement distribution through the segment by polynomial interpolation functions. By applying Hamilton’s principle, the dispersion equation is obtained as a standard algebraic eigenvalue problem. The reasonably good accuracy of the method is demonstrated for the lowest modes by comparing, where feasible, the results with analytical solutions. To demonstrate the method’s versatility, frequency spectra are also presented for I and L shaped cross sections.
Numerical Simulation of Swirl-Stabilized Premixed Flames With a Turbulent Combustion Model Based on a Systematically Reduced Six-Step Reaction Mechanism
Authors: Bohn D. E. , Lepers J.
Published: July 2002

This paper presents the application of a detailed combustion model for turbulent premixed combustion to a swirl-stabilized premix burner. Computations are carried out for atmospheric pressure and elevated pressure of 9 atm. Results of computations for atmospheric pressure are compared to experimental data. The combustion model is of the joint-pdf type. The model is based on the characteristics of turbulent combustion under conditions typical for gas turbine burners. It incorporates a systematically reduced six-step reaction mechanism yielding direct computation of radical concentrations via transport equations or steady-state assumptions. The model is able to simulate combustion of fuel gases containing methane, carbon monoxide, hydrogen, carbon dioxide, and water. It is therefore applicable to both methane and low-BTU fuel gas combustion. Based on computed radical concentrations, a post-processor for NOx formation is applied. This post-processor considers thermal formation of nitrogen oxides and NO formation via the nitrous oxide path.
Frictional Insertion Kinetics of Bone Biopsy Needles
Authors: Heiner Anneliese D. , Brown Thomas D. , Rossin Victor , Buckwalter Joseph A.
Published: July 2002

Patients undergoing a percutaneous bone biopsy often complain of pain during needle insertion, despite local anesthesia. Bone biopsy needles are typically inserted with combined axial and twisting motions. These motions could cause pain through frictional heating or direct mechanical irritation. The hypothesis of this study is that the insertion energy of bone biopsy needles can be reduced by modifying the insertion kinetics or by adding a friction-lowering coating to the needles. Jamshidi bone biopsy needles were driven into a bone analog model by an MTS materials testing machine operating under axial and rotational displacement control. The load/torque recordings showed that, to significantly decrease insertion energy and peak resistance to needle insertion, axial velocity and angular frequency had to be decreased to one quarter of the baseline, typical-usage parameters. However, the increased insertion time may not be acceptable clinically. The majority of the insertion energy was associated with the needle axial thrust rather than with needle twisting. Overcoming friction against the side of the needle consumed much more of the insertion energy than did the process of cutting per se. None of five needle coatings tested succeeded in appreciably lowering the insertion energy, and none achieved a substantial decrease in peak resisting force.
Tunable Athermal Multi-FBG Package Using a Bending Bimetal Structure
Authors: Lin Samuel I-En
Published: July 2002

The Fiber Bragg Gratings (FBGs) written by ultraviolet light into the core of an optical fiber have developed into a critical component for many applications in the fiber-optic communication system. A stable temperature compensation mechanism is essential to the successful usage of FBG-based devices. In this paper, the bimetal-based temperature-compensating package with tunable mechanism was developed. Such a tunable mechanism serves as prestress and post-tuning mechanisms of fixture in order to obtain a predetermined central wavelength. With the aid of developed experimental procedure, this compact and easily manufactured package can achieve temperature coefficient of 8.3×10−4 nm/°C in the temperature range from −40°C to 80°C. The same package can also be used for multi-FBG applications.
Heat Transfer in Rotating Narrow Rectangular Ducts With Heated Sides Parallel to the r-z Plane
Authors: Willett Fred T. , Bergles Arthur E.
Published: July 2002

In gas turbine blade design, a variety of channel shapes and orientations are used in the cooling circuit. Most of the rotating channel heat transfer research to date has considered channels of square or round cross-sections. This research characterizes the effect of rotation on fully developed turbulent convective heat transfer in ducts of narrow cross-section (height-to-width aspect ratio of 1:10). Experiments were conducted using ducts of narrow cross-section, oriented such that the long sides of the duct cross-section are perpendicular to the direction of blade tangential velocity (parallel to the r-z plane). In the experiment, a high-molecular-weight gas (Refrigerant-134A) at ambient pressure and temperature conditions was used to simulate coolant-to-wall density ratios that match engine conditions. Thin foil heaters were used to produce a uniform heat flux at the long sides of the duct; the narrow sides were unheated. Duct Reynolds numbers were varied up to 31,000; rotation numbers were varied up to 0.11. The test results show the effect of rotation and aspect ratio on duct leading and trailing side heat transfer. The results provide insight into the effect of rotation (Coriolis) in the absence of buoyancy effects. Comparisons with previously reported results are presented to show the effect of cross-section shape on rotating channel heat transfer.
Characterization and Detection of Crack-induced Rotary Instability
Authors: Yang B. , Suh C. S. , Chan A. K.
Published: July 2002

System instability and chaotic response are the failure modes that could significantly impact the reliability and operating safety of high-speed rotor-dynamical machines. Initiation and propagation of surface cracks in rotary shafts are common causes for such failure modes. To be able to detect the onset and progression of these faults will considerably extend the lifetime and improve the reliability of the mechanical system. A wavelet-based algorithm effective in identifying mechanical chaotic response has been applied to determine the nonlinear dynamical characteristics of a model-based, cracked rotor. This investigation confirms reported correlation of surface crack breathing with rotor chaotic motions. The effectiveness of the algorithm in detecting rotor-dynamic instability induced by mechanical faults as contrast to algorithms that are based on nonlinear dynamics is discussed. The results show not just the feasibility of the algorithm in mechanical fault diagnosis but also suggest its applicability to in-line, real-time condition monitoring at both the system and component levels.
Finite Element Analysis of a Computer Hard Disk Drive Under Shock
Authors: Lin Chen-Chi
Published: July 2002

Shock of computer hard disk drives (HDD) in both portable and desktop computers is a common problem. Shock of an HDD can occur during installing the HDD into the computer, HDD testing, HDD handling, and so forth. It is important to identify key design parameters to improve HDD shock performance. This paper presents the finite element studies of a HDD under a non-operational linear drop shock. A complete HDD model is built in ANSYS finite element package. GP commands are used to apply the preload and define the interface between the head and the disk. Shock pulses with different amplitudes and pulse widths are applied to the HDD. The minimum shock amplitude required to lift off the head from the disk is determined for different shock pulse width. Discrete Fourier Transform studies are used to identify critical frequency ranges for different shock pulse widths. The design guideline for the minimum space required between the swage plates and the disk is provided. The effects of drive base stiffness, disk thickness, actuator arm stiffness, and bearing stiffness on HDD shock performance are investigated.
An Automatic Method for Finding the Assembly Configurations of Planar Non-Single-Input-Dyadic Mechanisms
Authors: Foster D. E. , Cipra R. J.
Published: July 2002

This paper examines the problem of identifying the assembly configurations (ACs), also called circuits, of planar non-single-input-dyadic (NSID) mechanisms. An SID mechanism is a multi-loop mechanism which can be defined by adding one loop at a time such that the mechanism has one degree of freedom (DOF) after each loop is added. An NSID mechanism is any mechanism that does not meet the SID criterion. This includes all multi-DOF mechanisms, and some complex single-DOF mechanisms. An automatic method is presented which allows a computer to determine the ACs of an NSID mechanism. For single-DOF mechanisms, the ACs are represented by curves drawn in a plane represented by two joint variables. For multi-DOF mechanisms, the ACs consist of one or more regions in the plane, which are defined by the curves that bound them. The automated method finds these bounding curves, and then determines which curves belong to the same region, and which regions belong to the same AC. Mechanisms with pin joints and sliding joints are considered.
Models for Analysis of Water Hammer in Piping With Entrapped Air
Authors: Chaiko M. A. , Brinckman K. W.
Published: July 2002

Water hammer transients in a pipe line with an entrapped air pocket are analyzed with three one-dimensional models of varying complexity. The most simple model neglects the influence of gas-liquid interface movement on wave propagation through the liquid region and assumes uniform compression of the entrapped noncondensable gas. In the most complex model, the full two-region wave propagation problem is solved for adjoining gas and liquid regions with time varying domains. An intermediate model which allows for time variation of the liquid domain, but assumes uniform gas compression, is also considered. Calculations are carried out for a wide range of initial system pressure ranging from 0.101 MPa (14.7 psia) to 6.89 MPa (1000 psia). A step increase in pressure equal to 5 times the initial system pressure is imposed at the pipe inlet and the pressure response of the system is investigated. Results show that time variation of the liquid domain and nonuniform gas compression can be neglected for initial air volumes comprising 5% or less of the initial pipe volume. The uniform compression model with time-varying liquid domain captures all of the essential features predicted by the full two-region model for the entire range of pressure and initial gas volume considered in the study, and it is the recommended model for analysis of waterhammer in pipe lines with entrapped air.
Moment Lyapunov Exponents of a Two-Dimensional Viscoelastic System Under Bounded Noise Excitation
Authors: Xie W.-C.
Published: July 2002

The moment Lyapunov exponents of a two-dimensional viscoelastic system under bounded noise excitation are studied in this paper. An example of this system is the transverse vibration of a viscoelastic column under the excitation of stochastic axial compressive load. The stochastic parametric excitation is modeled as a bounded noise process, which is a realistic model of stochastic fluctuation in engineering applications. The moment Lyapunov exponent of the system is given by the eigenvalue of an eigenvalue problem. The method of regular perturbation is applied to obtain weak noise expansions of the moment Lyapunov exponent, Lyapunov exponent, and stability index in terms of the small fluctuation parameter. The results obtained are compared with those for which the effect of viscoelasticity is not considered.
Surface Instability of an Elastic Thin Film Interacting With a Suspended Elastic Plate
Authors: Ru C. Q.
Published: July 2002

This paper studies surface instability of a compliant elastic thin film on a rigid substrate interacting with a suspended elastic plate through van der Waals forces. The analysis is based on a novel method which permits a simple rational expression for the interaction coefficient as a function of the wave number of instability mode. The critical value of the interaction coefficient and the instability mode of the film-plate system can be determined easily by identifying the minimum of the interaction coefficient within an admissible range. When the stability strength of the plate is lower than the film even for the shortest plate-lengths, the interaction coefficient is found to be an increasing function of the wave number, and thus the film-plate system exhibits a long-wave instability mode determined by the suspended plate. In all other cases, the interaction coefficient admits an internal local minimum representing the short-wave mode of the film, and the critical value and instability mode of the film-plate system are determined by the internal local minimum for shorter plates, or by the long-wave mode of the plate for longer plates. Some numerical examples are given to illustrate the results.
Numerical Simulation of Polymer Flow Into a Cylindrical Cavity
Authors: Kumar Amit , Ghoshdastidar P. S.
Published: July 2002

In this paper, new finite-difference based detailed general methodologies are presented for numerical simulation of injection mold-filling during the production of a long cylindrical object. The polymer considered is low density polyethylene (LDPE) following power-law viscosity model for nonzero shear rate zone. However, where shear rate becomes zero, “zero-shear viscosity” value has been used. Three cases have been considered, namely; (i) isothermal filling at constant injection pressure; (ii) isothermal filling at constant flow rate and; (iii) nonisothermal filling at constant flow rate. For (iii), the viscosity of LDPE is also a function of temperature. The material of the mold is steel. For the nonisothermal filling, the concept of melt-mold thermal contact resistance coefficient has been incorporated into the model. The length and diameter of the body in all three cases have been taken as 0.254 m and 0.00508 m, respectively. The results show excellent agreement with the corresponding analytical solutions for the first two cases showing the correctness of the numerical method. The simulation results for nonisothermal filling are reported for the first time for this particular geometry and lend insight into various important aspects of mold-filling including injection pressure versus time, and effects of flow rates on melt temperature fields at various axial locations as well as on frozen skin layer.
An Improved Transfer Matrix Method for Steady-State Analysis of
Nonlinear Rotor-Bearing Systems
Authors: Zu J. W. , Ji Z.
Published: July 2002

An improved transfer matrix method is developed to analyze nonlinear rotor-bearing systems. The rotating shaft is described by the Timoshenko beam theory which considers the effect of the rotary inertia and shear deformation. A typical roller bearing model is assumed which has cubic nonlinear spring and linear damping characteristics. Transfer matrices for the Timoshenko shaft element, disk element, and nonlinear bearing element are derived and the global transfer matrix is formed. The steady-state response of synchronous, subharmonic, and superharmonic whirls is determined using the harmonic balance method. Two numerical examples are presented to demonstrate the effectiveness of this approach.
Influence of Thermal Effects on Hole Quality in Dry Drilling, Part 1: A Thermal Model of Workpiece Temperatures
Authors: Kalidas Shiva , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

A finite element thermal model is devised to capture the transient temperatures in the workpiece in drilling. Experimental observations along with an inverse heat conduction procedure is utilized in identifying the strength of the heat fluxes from the three distinct regions of the drill (drill body, cutting lips and chisel edge) at various process conditions in both wet and dry conditions with coated and uncoated drills. The identified heat fluxes along with a calibration scheme are used in predicting the transient temperatures in the workpiece in both dry and wet conditions. The model demonstrates the ability to predict the temperatures within 20 percent of the measured temperature rise.
Influence of Direct Normal Irradiance Variation on the Optimal Parabolic Trough Field Size: A Problem Solved with Technical and Economical Simulations
Authors: Quaschning Volker , Kistner Rainer , Ortmanns Winfried
Published: July 2002

One of the main problems when designing a solar thermal power plant is finding the optimal parabolic trough field size. Errors made in this context can easily lead to financial disaster. Simulation tools that handle all aspects of a power plant (technical as well as economical) treat such economical problems as a whole and can be very helpful during the design process. However, even the smartest simulation tool depends significantly on the input parameters, such as the solar irradiance. As a result of the given considerations, a new method for estimating the optimized solar field size as a function of the solar irradiance is proposed. Additionally, this paper demonstrates a path to simulate the complexity of a parabolic trough power plant.
Thermoelastic Fracture Mechanics for Nonhomogeneous Material Subjected to Unsteady Thermal Load
Authors: Wang B. L. , Han J. C. , Du S. Y.
Published: July 2002

This article provides a comprehensive treatment of cracks in nonhomogeneous structural materials such as functionally graded materials. It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using a laminated composite plate model to simulate the material nonhomogeneity, we present an algorithm for solving the system based on the Laplace transform and Fourier transform techniques. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problems in the functionally graded materials with arbitrarily varying material properties. The algorithm can be applied to steady state or transient thermoelastic fracture problem with the inertial terms taken into account. As a numerical illustration, transient thermal stress intensity factors for a metal-ceramic joint specimen with a functionally graded interlayer subjected to sudden heating on its boundary are presented. The results obtained demonstrate that the present model is an efficient tool in the fracture analysis of nonhomogeneous material with properties varying in the thickness direction. [S0021-8936(00)01601-9]
The Micromechanical Environment of Intervertebral Disc Cells: Effect of Matrix Anisotropy and Cell Geometry Predicted by a Linear Model
Authors: Baer Anthony E. , Setton Lori A.
Published: July 2002

Cells of the intervertebral disc exhibit spatial variations in phenotype and morphology that may be related to differences in their local mechanical environments. In this study, the stresses, strains, and dilatations in and around cells of the intervertebral disc were studied with an analytical model of the cell as a mechanical inclusion embedded in a transversely isotropic matrix. In response to tensile loading of the matrix, the local mechanical environment of the cell differed among the anatomic regions of the disc and was strongly influenced by changes in both matrix anisotropy and parameters of cell geometry. The results of this study suggest that the local cellular mechanical environment may play a role in determining both cell morphology in situ and the inhomogeneous response to mechanical loading observed in cells of the disc. [S0148-0731(00)00603-8]
Structural Integrity of a Standpipe Component in a Petrochemical Catalytic Cracking Unit: Part 1—Assessment of Creep Rupture Properties
Authors: de O. Bueno Levi , Marino Luiz , Serra Flavio A. S. , Gazini Fernando T.
Published: July 2002

During a shutdown for general maintenance of a catalytic cracking unit, intergranular cracks were observed to occur during welding of the regenerator’s standpipe component manufactured from 2 1/4 Cr-1Mo steel. The cracking was observed to be related to intensive carbide precipitation in grain boundaries. To overcome the problem it was decided to heat-treat the relevant section of the component to dissolve these carbides and make possible its welding to a new virgin section of the tube. Samples of the material in its various conditions (virgin, ex-service, heat-treated and welded) were taken to check the efficiency of the thermal treatment in reducing the embrittlement effects and to carry out a general assessment of the remaining life of the component related to creep behavior considering smooth bar creep specimens. [S0094-4289(00)00403-5]