bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of cyclic GMP‐dependent protein kinase in the contractile response to exogenous nitric oxide in rat cardiac myocytes
Authors: Layland Joanne , Li Jian‐Mei , Shah Ajay M.
Published: July 2002

Nitric oxide (NO) can directly modulate cardiac contractility by accelerating relaxation and reducing diastolic tone. The intracellular mechanisms underlying these contractile effects are poorly understood. Here we investigate the role of cyclic GMP‐dependent protein kinase (PKG) in the contractile response to exogenous NO in rat ventricular myocytes. Isolated ventricular myocytes were stimulated electrically and contractility was assessed by measuring cell shortening. Some cells were loaded with the fluorescent Ca2+ probe indo‐1 AM for simultaneous assessment of the intracellular Ca2+ transient. The NO donor diethylamine NONOate (DEA/NO, 10 μm) significantly increased resting cell length, reduced twitch amplitude and accelerated time to 50 % relaxation (to 100.8 ± 0.2, 83.7 ± 3.0 and 88.9 ± 3.7 % of control values, respectively). The contractile effects of DEA/NO occurred without significant changes in the amplitude or kinetics of the intracellular Ca2+ transient, suggesting that the myofilament response to Ca2+ was reduced. These effects were abolished by inhibition of either guanylyl cyclase (with 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one; ODQ, 10 μm) or PKG (with Rp‐8‐Br‐cGMPs, 10 μm) suggesting that, at the concentration investigated, the effects of DEA/NO were mediated exclusively by PKG, following activation of guanylyl cyclase and elevation of cGMP. Direct activation of PKG with 8‐pCPT‐cGMP (10 μm) mimicked the effects of DEA/NO (resting cell length and time to 50 % relaxation were 100.6 ± 0.1 and 90.5 ± 1.5 % of control values, respectively).The reduced myofilament Ca2+ responsiveness was not attributable to an intracellular acidosis since the small reduction in pHi induced by DEA/NO was found to be uncoupled from its contractile effects. However, hearts treated with DEA/NO (10 μm) showed a significant increase (1.4‐fold; P < 0.01) in troponin I phosphorylation compared to control, untreated hearts. These results suggest that the reduction in myofilament Ca2+ responsiveness produced by DEA/NO results from phosphorylation of troponin I by PKG.
An Approach for Modeling Sheet Metal Forming for Process Controller Design
Authors: Hsu C.-W. , Ulsoy A. G. , Demeri M. Y.
Published: July 2002

Varying the blank holder force during forming can lead to higher formability and accuracy, and better part consistency. Process control, using on-line adjustment of the blank holder force to follow a reference process variable (e.g., the punch force, the draw-in, etc.) trajectory has been applied to sheet metal forming. However, process controller design has not been thoroughly addressed. In this paper, the essential part for systematic process controller design, i.e., modeling a sheet metal forming process, will be addressed in terms of control terminology (e.g., the process model, the model uncertainty and the disturbance). A process model for u-channel forming, i.e., a mathematical relationship between the blank holder force and the punch force, is presented and experimentally validated. Characterization of the model uncertainty mainly due to small variations in blank size, sheet thickness, material properties and tooling shape due to die wear and the disturbance which is mainly due to friction is developed. [S1087-1357(00)01304-6]
A Flow Visualization Study of Vortex Interaction With the Wake of a Sphere
Authors: Sun M. , Marshall J. S.
Published: July 2002

A study of the interaction between an initially columnar intake vortex (hereinafter referred to as the primary vortex) and vortex structures in the wake of a single sphere (hereinafter referred to as secondary vortices) is performed using a series of flow visualization experiments, in which a sphere is towed toward a stationary vortex with ambient axial flow and gradually decelerated to rest at a specified distance from the vortex core axis. Both the primary vortex core and the boundary layer of the sphere are visualized using laser-induced fluorescent dyes of two different colors, which are illuminated either with a laser sheet or a laser volume. The strength of the primary vortex is measured using particle-image velocimetry, which is also used to measure the strength of the secondary vortices in select cases. The form of the sphere wake in the presence of the primary vortex and the effect of the induced velocity from the secondary vortices on the primary vortex are studied for different values of the vortex-sphere separation distance, the sphere diameter, and the primary vortex core radius. Weak secondary vortices are observed to induce formation of small-amplitude waves of varying core area on the primary vortex, eventually forming a turbulent sheath surrounding the primary vortex. Stronger secondary vortices have an increasingly strong effect on the primary vortex, including large-amplitude variation in core area, outward ejection of fluid from the primary vortex core, and breakdown of the primary vortex. [S0098-2202(00)01403-6]
Reconditioning of Gas Turbine Components by Heat Treatment
Authors: Brown J. A. , Freer R. , Rowley A. T.
Published: July 2002

At the high operating temperatures experienced within a gas turbine, creep damage is a major life-limiting factor. This is especially true for components which are highly stressed and closest to the hot gas inlet end of the machine, such as the rotating blades in this area. The ability to recover the creep properties of used gas turbine components might enable their service lives to be increased considerably. Thereby, maintenance costs could be reduced. Previous research into the feasibility of reconditioning crept superalloys by heat treatment will be reviewed and perceived limitations identified. The current work will add to knowledge on the effects of conventional recovery techniques and will explore potential new heat treatment regimes. The experimental and analytical methods to be used will be both described and supported by preliminary results.
Dust Generation Properties of Solid Lubricant Film Coated and Perfluoropolyether Lubricated Ball Bearings
Authors: Miyake Shojiro
Published: July 2002

The purpose of this work is to elucidate the properties of ball bearings used for clean applications. Dust, namely wear debris particle generation behavior of ball bearings lubricated with solid lubricant films and low vapor pressure PFPE (perfluoropolyether) grease was investigated using a laser scattering type dust counter under small-angle oscillatory conditions. In the case of the solid lubricated bearing, dust generation began to increase rapidly at a certain number of oscillatory cycles, as deduced from the bearing surface damage. Bearings lubricated with a MoS2/Ag layer and MoS2 sputtered films showed less dust generation, starting torque and surface damage than ion-plated Ag and Au film lubricated and unlubricated bearings. Dust generation was deduced to be due to the damage formation of oscillatory ball bearings, based on the size of the contact elliptic area. The total number of particles generated from the ball bearing lubricated with PFPE grease is very large, but bearing damage is very small. Degraded PFPE was observed on the side plate seal by FTIR. Therefore, dust generation from a PFPE-lubricated bearing is deduced to be due to PFPE degradation. Particles generated from bearings with dry contact include large particles. In contrast, most of the particles generated from bearings lubricated with PFPE grease are very small. Side plate seals of ball bearings decrease the amount of dust generated from these bearings. [S0742-4787(00)00704-9]
Topological Synthesis of Fractionated Geared Differential Mechanisms
Authors: Chen Dar-Zen , Yao Kang-Li
Published: July 2002

An efficient and systematic methodology for the topological synthesis of admissible fractionated geared differential mechanisms is presented. Based on the extension of the 2-dof automotive gear differential, it is shown that a fractionated geared differential mechanism can be decomposed into a main component and an input component. Characteristics of these two components are laid out, and the atlases of admissible input and main components are identified from the existing atlases of non-fractionated geared kinematic chains. With a systematic procedure to choose input and main components and select admissible connecting links, fractionated geared differential mechanisms with three and four input/output links are generated accordingly. [S1050-0472(00)00804-7]
A Sliding Mode Static Output Feedback Controller Based on Linear Matrix Inequalities Applied to an Aircraft System
Authors: Edwards Christopher , Spurgeon Sarah K. , Akoachere Ashu
Published: July 2002

This paper presents a variable structure control design methodology for multi-input uncertain dynamic systems using only plant output information. Static output feedback is utilized in the design of the switching surface using a Linear Matrix Inequality approach recently proposed in the literature. A novel LMI based optimization approach is subsequently employed in the construction of the control law to guarantee that a sliding motion takes place. The efficacy of the algorithms is demonstrated on a nontrivial design example—an aircraft system representation which includes the flexible modes of the airframe. [S0022-0434(00)00204-5]
Autoclave Reliability of MEMS Pressure and Temperature Sensors Embedded in Carbon Fiber Composites
Authors: Javidinejad Amir , Joshi Shiv P.
Published: July 2002

In this paper, embedding of surface mount pressure and temperature sensors in the carbon fiber composites are described. Commercially available surface mount pressure and temperature sensors are used for embedding in a composite lay-up of IM6/HST-7, IM6/3501, and AS4/E7T1-2 prepregs. The fabrication techniques developed here are the focus of this paper. A successful embedding procedure of pressure and temperature sensors in fibrous composites is described in detail. The description includes techniques for positioning and insulating the sensors and the lead wires from the conductive carbon prepregs. Procedural techniques are developed and discussed for isolating the pressure sensor’s flow-opening, from the exposure to the prepreg epoxy flow and exposure to the fibrous particles, during the autoclave curing of the composite laminate. The effects of the autoclave cycle (if any) on the operation of the embedded pressure and temperature sensors are discussed.
The Maximum Stress in Optical Glass Fibers Under Two-Point Bending
Authors: Muraoka Mikio
Published: July 2002

The maximum stress in optical glass fibers subjected to two-point bending was evaluated by E. Suhir, “Effect of the Nonlinear Behavior of the Material on Two-Point Bending of Optical Glass Fibers,” ASME Journal of Electronic Packaging, Vol. 114, pp. 246–250, taking into account the shift in the neutral axis due to the nonlinear stress-strain relationship of the materials. However, the resulting distribution of bending stress on the fiber cross-section is not realistic because it produces a nonzero axial force. In the present study, we derive the correct formulas for evaluating the maximum stress under the valid condition that the bending stress does not contribute to the axial force. Moreover, we employ the nonlinear stress-strain relationship containing a third-order term of strain, which is more appropriate for the materials than that utilized by Suhir.
Review of Models and the Disturbed State Concept for Thermomechanical Analysis in Electronic Packaging
Authors: Desai Chandra S. , Whitenack Russell
Published: July 2002

A number of models for thermomechanical stress analysis and fatigue failure of materials are reviewed and their capabilities and limitations are identified. The unified disturbed state concept (DSC) for constitutive modeling of materials and interfaces is presented and compared with other approaches. An approximate procedure based on the DSC is proposed for accelerated design-analysis and cyclic fatigue failure. Solutions of example problems using the DSC and associated computer (FE) procedures are included to illustrate its integrated and improved capabilities for analysis of stresses, strains, microcracking, fracture and fatigue failure, and reliability.
Bauschinger Effect Design Procedures for Compound Tubes Containing an Autofrettaged Layer
Authors: Parker Anthony P.
Published: July 2002

Autofrettage is used to introduce advantageous residual stresses into pressure vessels. The Bauschinger effect can produce less compressive residual hoop stresses near the bore than are predicted by “ideal” autofrettage solutions. A design procedure was recently proposed which models material removal from the bore or outside diameter of a single, plain autofrettaged tube in the presence of Bauschinger effect. This paper extends the procedure to model the addition of pressure or of material (via shrink-fit) to the tube, providing associated residual stress profiles following various amounts of further yielding due to a net external pressure. Simple criteria are developed for determining, and avoiding, further yielding in the autofrettaged tube when it is used as part of a compound assembly involving shrink-fitting; these criteria are based upon net pressure differential between the bore and outside diameter of the autofrettaged tube. An alternative criterion, based upon bore hoop stress, is shown to be erroneous.
In-Cylinder Tumble Flow Field Measurements and Predictions
Authors: Hong C.-W. , Tarng S.-D.
Published: July 2002

This paper presents the comparison between measured and predicted results of the in-cylinder tumble flow generated by a port-valve-liner assembly on a steady-flow test bench. The purpose was to advance the understanding of the stationary turbulence process via experimental and computational techniques in the same time. A baseline single-cylinder 4-stroke motorcycle engine was chosen. Its liner was replaced by a transparent acrylic-plastic tube and the piston was removed. This was to focus the research on the tumble flow generated by the geometry of its port, the passage of the canted inlet valve, and a dome-shaped combustion chamber. The in-cylinder turbulent flow field was measured via a 3-component laser Doppler velocimeter (LDV) point by point. A simultaneous computer simulation was carried out to predict the in-cylinder flow field of the same engine under the same operating condition, using KIVA3V—the most recent version of the KIVA code. The mean speed, turbulence intensity, tumble ratio, swirl ratio, and vortex circulation from both skills were all compared. A reasonably good level of agreement has been achieved. Both modern techniques are also validated.
Interconnection of Distributed Components: An Overview of Current Middleware Solutions*
Authors: Urban Susan D. , Dietrich Suzanne W. , Saxena Akash , Sundermier Amy
Published: July 2002

From design and manufacturing to electronic commerce, coordinating business activities in engineering applications requires accessing data and software from distributed sources. The Common Object Request Broker Architecture (CORBA) of the Object Management Group emerged in the 1990’s as a standard for access to distributed software components. Since that time, the standard has matured significantly, providing advanced features for event notification and transaction processing. At the same time, Java-based technology for distributed object computing has also emerged, from Remote Method Invocation to Enterprise JavaBeans, Jini Connection Technology, JavaSpaces, Java Messaging Service, and Java Transaction Service. Sorting through the options available for the use of such tools can be a difficult task. This paper provides an overview of CORBA and Java technology for distributed object computing. A comparison of these different technologies is presented, discussing the similarities and differences, as well as the way in which such tools can be used together for distributed access to the types of software and data components that are needed for the construction of distributed engineering applications. Future directions for the use of such tools are also identified.
Generalized Bending of a Large, Shear Deformable Isotropic Plate Containing a Circular Hole or Rigid Inclusion
Authors: Bert C. W. , Zeng H.
Published: July 2002

The problem of a large isotropic plate with a circular hole or rigid circular inclusion is considered here. The plate experiences transverse shear deformation and is subjected to an arbitrary bending field. By using Reissner’s plate theory, a general solution, in terms of Poisson’s ratio ν, a geometric ratio, and bending moment ratio B, is obtained to satisfy both the boundary conditions along the edge and at great distances from the edge. The stress couple concentration factors are calculated and compared with classical plate theory, three-dimensional elasticity theory, higher-order plate theory, and an experimental result.
Multiaxial Stress Concentration in Filleted Shafts
Authors: Rolovic Radovan , Tipton Steven M. , Sorem, James R.
Published: July 2002

In a previous paper, popular stress concentration factor charts for shoulder filleted shafts in bending and tension were shown to be in error, and more accurate solutions were published. In this paper, improved stress concentration factor information is presented for torsional loading, based on detailed finite element analyses. The new solutions agree with previous design charts, but cover a wider range of geometries. A concise engineering equation is presented for the stress concentration factor and maximum equivalent stress under each of three loading modes, along with another equation that reveals the location of each maximum stress component in the fillet. It is shown that the maximum stress locations for bending and tension loading are approximately the same, but can differ significantly from the maximum torsional stress location. In those cases, sharp surface gradients can cause the maximum equivalent notch stress under combined bending/axial and torsional loading to be overestimated when computed based on the maximum stress concentration factors for each load component. An example is used to demonstrate how the surface strain gradient causes the placement and size of a strain gage to have a strong influence on strain measurements.
Hamilton Principle and Generalized Variational Principles of Linear Thermopiezoelectricity
Authors: He Ji-Huan
Published: July 2002

Via the semi-inverse method, a family of various variational principles is established for thermopiezoelectricity, including a Hamilton principle and a minimum complementary energy principle.
Frictionally Excited Thermoelastic Instability in Multi-Disk Clutches and Brakes
Authors: Decuzzi P. , Ciaverella M. , Monno G.
Published: July 2002

The propensity toward thermoelastic instability (TEI) in multi-disk clutches and brakes is investigated by introducing a new bidimensional analytical model, where metal and friction disks are replaced by two-dimensional layers of finite thickness. This new model permits to estimate the effect of the thickness ratio a1/a2, between friction and metal disks, on the critical speed, critical wave parameter and migration speed of the sliding system. It is found that as the thickness ratio a1/a2 decreases the critical speed reduces significantly taking up values about 80 percent smaller than that predicted by previous two-dimensional models for commonly used ratios 0.1<a1/a2<1, whilst the critical wave parameter slightly increases. Therefore, not only the susceptibility towards TEI can be reduced by changing the material properties of the friction lining but also by adjusting suitably the thickness ratio of the disks. The two-dimensional model is also employed to determine the critical speed in a real multi-disk clutch, and the results are compared with a three-dimensional finite element code. It is shown that the critical speed estimated by the present two-dimensional plane strain model is in good agreement with that determined by the FE code for sufficiently large radial thickness of the disks, whilst the two-dimensional plane stress solution has to be used for relatively small radial thickness ratios. Also, it is found that the critical number of hot spots is independent of the radial thickness ratio and it is correctly predicted by the two-dimensional model.
A New Method for Calculating Bending Moment and Shear Force in Moving Load Problems
Authors: Pesterev A. V. , Tan C. A. , Bergman L. A.
Published: July 2002

In this paper, a new series expansion for calculating the bending moment and the shear force in a proportionally damped, one-dimensional distributed parameter system due to moving loads is suggested. The number of moving forces, which may be functions of time and spatial coordinate, and their velocities are arbitrary. The derivation of the series expansion is not limited to moving forces that are a priori known, making this method also applicable to problems in which the moving forces depend on the interactions between the continuous system and the subsystems it carries, e.g., the moving oscillator problem. A main advantage of the proposed method is in the accurate and efficient evaluation of the bending moment and shear force, and in particular, the shear jumps at the locations where the moving forces are applied. Numerical results are presented to demonstrate the rapid convergence of the new series representation.
Nonlinear Stability Analysis of the Thin Micropolar Liquid Film Flowing Down on a Vertical Cylinder
Authors: Cheng Po-Jen , Chen Cha’o-Kuang , Lai Hsin-Yi
Published: July 2002

This paper investigates the weakly nonlinear stability theory of a thin micropolar liquid film flowing down along the outside surface of a vertical cylinder. The long-wave perturbation method is employed to solve for generalized nonlinear kinematic equations with free film interface. The normal mode approach is first used to compute the linear stability solution for the film flow. The method of multiple scales is then used to obtain the weak nonlinear dynamics of the film flow for stability analysis. The modeling results indicate that both subcritical instability and supercritical stability conditions are possible to occur in a micropolar film flow system. The degree of instability in the film flow is further intensified by the lateral curvature of cylinder. This is somewhat different from that of the planar flow. The modeling results also indicate that by increasing the micropolar parameter K=κ/μ and increasing the radius of the cylinder the film flow can become relatively more stable traveling down along the vertical cylinder.
Chemical Vapor Deposition of TBC: An Alternative Process for Gas Turbine Components
Authors: Wahl G. , Nemetz W. , Giannozzi M. , Rushworth S. , Baxter D. , Archer N. , Cernuschi F. , Boyle N.
Published: July 2002

This paper deals with the development of a new process for the deposition of thermal barrier coatings (TBC) based on chemical vapor deposition (CVD). The research program started in September 1998 under a BRITE/Euram III project. The CVD process involves the evaporation of zirconium and yttrium starting from metal-organic precursors and their reaction with oxygen in a hot wall reactor in order to deposit TBC layers. The influence of different deposition parameters such as evaporation temperature, pressure, and substrate temperature on structure, deposition rate, and process yield are described. The characterization of different precursors behavior is also described. Preliminary results, obtained with optimized conditions, have shown ZrO2-Y2O3 columnar layers with deposition rates of interest from an industrial point of view.
Detailed Heat Transfer Coefficient Distributions on a Large-Scale Gas Turbine Blade Tip
Authors: Teng Shuye , Han Je-Chin , Azad G. M. S.
Published: July 2002

Measurements of detailed heat transfer coefficient distributions on a turbine blade tip were performed in a large-scale, low-speed wind tunnel facility. Tests were made on a five-blade linear cascade. The low-speed wind tunnel is designed to accommodate the 107.49 deg turn of the blade cascade. The mainstream Reynolds number based on cascade exit velocity was 5.3×105. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The wake Strouhal number was kept at 0 or 0.1. The central blade had a variable tip gap clearance. Measurements were made at three different tip gap clearances of about 1.1 percent, 2.1 percent, and 3 percent of the blade span. Static pressure distributions were measured in the blade mid-span and on the shroud surface. Detailed heat transfer coefficient distributions were measured on the blade tip surface using a transient liquid crystal technique. Results show that reduced tip clearance leads to reduced heat transfer coefficient over the blade tip surface. Results also show that reduced tip clearance tends to weaken the unsteady wake effect on blade tip heat transfer.
An in Vitro Model of Neural Trauma: Device Characterization and Calcium Response to Mechanical Stretch
Authors: Geddes Donna M. , Cargill Robert S.
Published: July 2002

An in vitro model for neural trauma was characterized and validated. The model is based on a novel device that is capable of applying high strain rate, homogeneous, and equibiaxial deformation to neural cells in culture. The deformation waveform is fully arbitrary and controlled via closed-loop feedback. Intracellular calcium [Ca2+]i alterations were recorded in real time throughout the imposed strain with an epifluorescent microscopy system. Peak change in [Ca2+]i, recovery of [Ca2+]i, and percent responding NG108-15 cells were shown to be dependent on strain rate (1−1 to 10−1) and magnitude (0.1 to 0.3 Green’s Strain). These measures were also shown to depend significantly on the interaction between strain rate and magnitude. This model for neural trauma is a robust system that can be used to investigate the cellular tolerance and response to traumatic brain injury.
Comparison of Different Subgrid-Scale Models of Large Eddy Simulation for Indoor Airflow Modeling
Authors: Su Mingde , Chen Qingyan , Chiang Che-Ming
Published: July 2002

The Smagorinsky subgrid-scale model, a dynamic subgrid-scale model, and a stimulated subgrid-scale model have been used in a large eddy simulation (LES) program to compute airflow in a room. A fast Fourier transformation (FFT) method and a conventional iteration method were used in solving the Poisson equation. The predicted distributions of indoor air velocity, temperature, and contaminant concentrations show that the three subgrid-scale models can produce acceptable results for indoor environment design. The dynamic and stimulated models performed slightly better than the Smagorinsky model. The use of FFT can significantly reduce the computing time. LES is a tool of the next generation of indoor air distribution design.
A Novel Technique in the Solution of Axisymmetric Large Deflection Analysis of a Circular Plate
Authors: Ramachandra L. S. , Roy D.
Published: July 2002

In the present paper a new linearization technique referred to as the locally transversal linearization (LTL) is used for large deflection analyses of axisymmetric circular plates. The LTL procedure, where solution manifolds of linearized equations are made to intersect transversally those of the nonlinear ordinary differential equations, reduces the given set of nonlinear ordinary differential equations to a set of nonlinear algebraic equations in terms of a descretized set of unknown response vectors.
Asymptotic Rejection of Periodic Disturbances With Fixed or Varying Period
Authors: Yu Shiang-Hwua , Hu Jwu-Sheng
Published: July 2002

A constructive derivation of repetitive control is obtained, through attempting to derive a control law for asymptotic rejection of periodic disturbances. This derivation not only reveals a close relationship between iterative operator inversion and repetitive control, but also suggests a unified design method for a learning control algorithm. Also, based on the observation, digital repetitive control can be generalized to reject periodic disturbance whose period is not exactly an integer multiple of the sampling interval. This study introduces a delay filter in the digital repetitive control law, which optimally interpolates the signal between samples, thus effectively reconstructing the signal of the previous period and making the learning process of repetitive control successful. The proposed optimal delay filter can be updated easily according to different signal periods. Thus it is specifically suitable for on-line tuning when the signal period is changing. Compared with the available tuning methods, the proposed tuning method has excellent steady-state performance while maintaining fast transient and system robustness. The simulations on active noise cancellation within a duct confirm the superiority of this tuning method.
Generation of Cyclic Stress-Strain Curves for Sheet Metals
Authors: Zhao K. M. , Lee J. K.
Published: July 2002

The main objective of this paper is to obtain the first few stress-strain loops of sheet metals from reverse loading so that the springback can be simulated accurately. Material parameters are identified by an inverse method within a selected constitutive model that represents the hardening behavior of materials subjected to a cyclic loading. Three-point bending tests are conducted on sheet steels (mild steel and high strength steel). Punch stroke, punch load, bending strain, and bending angle are measured directly during the tests. Bending moments are then computed from these measured data. Bending moments are also calculated based on a constitutive model. Normal anisotropy and nonlinear isotropic/kinematic hardening are considered. Material parameters are identified by minimizing the normalized error between two bending moments. Micro-genetic algorithm is used in the optimization procedure. Stress-strain curves are generated with the material parameters found in this way, which can be used with other plastic models.
Effects of Reynolds Number and Pressure Ratio on Leakage Loss and Heat Transfer in a Stepped Labyrinth Seal
Authors: Willenborg K. , Kim S. , Wittig S.
Published: July 2002

The influence of Reynolds number and pressure ratio on the operating characteristics of a stepped labyrinth seal was experimentally determined. The geometries investigated represent designs of a stepped labyrinth seal typical for modern jet engines. Heat transfer and discharge measurements were obtained for two plane models with various seal clearances. The experiments covered a range of Reynolds numbers and pressure ratios. Independent variation of Reynolds number and pressure ratio was obtained by adjusting the back pressure at the seal exit for a given pressure ratio. Dimensionless discharge coefficients, describing the sealing performance, were derived from the measured leakage rates. Pressure ratio, Reynolds number, tip geometry, and seal clearance all affected the sealing performance. Finite element calculations were employed to calculate the local heat transfer coefficients from the measured wall and gas temperatures. Averaging of the local values yielded mean heat transfer coefficients and mean Nusselt numbers. The heat transfer was mainly determined by the Reynolds number. Compressibility effects on the heat transfer were observed to be very small.
Spatial Free Plastic Forming of Slender Parts—Machine Design, Forming Limits, and Application
Authors: Thalmair M. , Lippmann H. , Reigl M.
Published: July 2002

Free plastic forming of a slender part means that an initially straight bar, clamped at its both ends, is bent and twisted by an appropriate motion of the end supports only. Emphasis is attached on the computer controlled, precise forming of workpieces with prescribed shape. In this paper the design of an appropriate forming machine at the laboratory scale will be presented. Moreover, the forming limits due to replastification of already completed sections of the part will be illustrated geometrically using one or two “cylinders of admissibility.” Finally, the method will be demonstrated by means of actually formed parts.
On a General Method of Unsteady Potential Calculation Applied to the Compression Stages of a Turbomachine—Part I: Theoretical Approach
Authors: Bakir F. , Kouidri S. , Belamri T. , Rey R.
Published: July 2002

An algorithm using the singularity method was developed. It allows taking into account the interaction between fixed and mobile cascades. Its principle is based on the summation of discrete vortices distributed periodically on the rotor and stator profiles. The overall matrix, obtained by applying the boundary conditions, takes into account the complexity of the studied cascade geometry (presence or not of splitter blades, possibly variable pitch of the profiles, etc…) To illustrate the interest and the impact of the algorithm, two parametric studies on turbomachines cascade are presented: Planes cascade made up of a rotor and a stator (at the mean radius of an axial fan). Circular cascade made up of impeller and a volute (peripheral cascade of a centrifugal pump).
Analyical Solutions for Failure Evolution With a Nonlinear Local Damage Model
Authors: Xin X. , Chicone C. , Chen Z.
Published: July 2002

The partitioned-modeling and similarity methods are applied in this paper to derive a closed-form solution for localized dynamic failure problems, with a nonlinear local damage model. The initial point of the localization is taken as the point at which the type of governing differential equation transforms from being hyperbolic to elliptic for dynamic case due to material damage. The evolution of localization is represented by a moving material surface of discontinuity between the elliptic domain and hyperbolic domain. A closed-form solution for a static loading case is also given as a complementary note to show evolution of the localized failure. The effects of model parameters on the structural response are investigated, and the evolution of relevant field variables is illustrated to demonstrate the essential feature of the localized failure evolution.
Physical Modeling of Wind Load on a Floating Offshore Structure
Authors: Bobillier Bertrand , Chakrabarti Subrata , Christiansen Poul
Published: July 2002

Wind is an important environmental parameter that influences the design of floating offshore structures, particularly in harsh environment. Because wind spectrum is broad-banded, computation of wind load on the floating structure is complicated. Moreover, the wind-induced slow-drift oscillation is an important design criterion. Simulated environment in a model test often includes wind effect. Accurate modeling of wind in a laboratory environment is, however, a difficult task. The wind tunnel provides a steady load on the superstructure quite accurately, but fails to show the effect of the changing free surface as well as dynamic effect. Therefore, simultaneous simulation of wind in the wave basin is desirable. A weight representing the steady wind load with a string and pulley arrangement at the center of the application of the superstructure is inadequate since it fails to simulate the variation of the wind spectrum. The generation and control of the design wind spectrum by an overhead bank of fans facing the model superstructure is an extremely difficult task due to large windage area. This paper presents an accurate and highly controllable method of the generation of variable wind simultaneously with waves and current in the wave basin that can be used with a variety of floating structure model. The concept was originally proposed by Kvaerner Oil & Gas International and implemented by the offshore model basin (OMB). In this method, a fan equipped with a constant-speed motor and blades with an adjustable pitch angle is directly mounted on the model deck above water. A digital signal generated from the specified wind spectrum is used to run the fan much like the wavemaker. A feedback system ensures the proper generation of the wind with the model motion. The method was successfully applied in several model tests of deepwater floating structures in which broad-banded wind spectra were generated. An example from an earlier such test is given here. The importance of the effect of the simulated wind spectrum on floating structures should be clear to a design engineer from this example.
A Study of Residual Stresses and Microstructure in 2024-T3 Aluminum
Friction Stir Butt Welds
Authors: Sutton M. A. , Reynolds A. P. , Wang D.-Q. , Hubbard C. R.
Published: July 2002

Three-dimensional residual stress mapping of an aluminum 2024-T3 arcan specimen, butt-welded by the friction stir technique, was performed by neutron diffraction. Results indicate that the residual stress distribution profiles across the weld region are asymmetric with respect to the weld centerline, with the largest gradients in the measured residual stress components occurring on the advancing side of the weld, with the longitudinal stress, σL, oriented along the weld line, as the largest stress. Within the region inside the shoulder diameter, the through-thickness stress, σZ, is entirely compressive, with large gradients occurring along the transverse direction just beyond the shoulder region. In addition, results indicate a significant reduction in the observed residual stresses for a transverse section that was somewhat closer to the free edge of an Arcan specimen. Microstructural studies indicate that the grain size in the weld nugget, is approximately 6.4 microns, with the maximum extent of the recrystallized zone extending to 6 mm on each side of the weld centerline. Outside of this region, the plate material has an unrecrystallized grain structure that consists of pancake shaped grains ranging up to several mm in size in two dimensions and 10 microns in through-thickness dimension.
A Real Parameter Continuation Method for Complete Solution of Forward Position Analysis of the General Stewart
Authors: Mu Zongliang , Kazerounian Kazem
Published: July 2002

Stewart Platform is a six degree of freedom, parallel manipulator, which consists of a base platform, a coupler platform and six limbs connected at six distinct points on the base platform and the coupler platform. The forward position analysis problem of Stewart Platform amounts to finding all its possible configurations based on the knowledge of the lengths of its limbs. In this paper, we present a numerical method for solving the forward position analysis problem for the most general Stewart Platform. This is a numerical method based on the polynomial continuation as established in recent works in the literature. However, one main difference is that the start system and the homotopy used here are based on physical design rather than pure mathematical equations. First, the target Stewart Platform is geometrically simplified into a platform, which, as the start platform, can be solved analytically. Then, a homotopy is constructed between the kinematics equations of the start platform and those of the target platform. By changing the parameters of the start platform incrementally into the parameters of the target system while tracking solutions of the start platform, a complete set of 40 solutions to the target platform can be found. Through this process, all of the extraneous paths have been eliminated before the solution tracking procedure starts and only isolated solutions of the start platform are tracked. The process for solutions to switch between real and complex is examined.
A Technique for Deducing In-Plane Modulus and Coefficient of Thermal
Expansion of a Supported Thin Film
Authors: Chiang Martin Y. M. , Chiang Chwan K. , Wu Wen-li
Published: July 2002

A technique for determining the in-plane modulus and the coefficient of thermal expansion (CTE) of supported thin films has been developed. The modulus and CTE are calculated by solving two coupled equations that relate the curvature of film samples deposited on two different substrates to the thermal and mechanical properties of the constituents. In contrast with the conventional method used to calculate modulus and CTE, which involves differentiation of the thermal stress in the film, this new technique does not require the differentiation of the thermal stress, and can also provide the temperature-dependence of the in-plane CTE and elastic modulus of supported thin films. The data reduction scheme used for deducing CTE and elastic modulus is direct and reliable.
Influence of Air Temperature Change on Equilibrium Velocity of Pneumatic Cylinders
Authors: Kagawa Toshiharu , Tokashiki Luis R. , Fujita Toshinori
Published: July 2002

This paper shows that equilibrium velocity of pneumatic cylinders not only depends on the effective area of the outlet speed control valve but also on the air temperature at the discharge chamber. Different equilibrium velocities were obtained experimentally with the same speed control valves, when load mass or initial pressure at the discharge chamber was changed. The different equilibrium velocities are explained by the air temperature change. Experiments are simulated using a cylinder model considering heat transfer. Experimental and simulation results are in good agreement.
Robust Stabilization of Large Amplitude Ship Rolling in Beam Seas
Authors: Chen Shyh-Leh , Shaw Steven W. , Khalil Hassan K. , Troesch Armin W.
Published: July 2002

The dynamics and control of a strongly nonlinear 3-DOF model for ship motion are investigated. The model describes the roll, sway, and heave motions occurring in a vertical plane when the vessel is subjected to beam seas. The ship is installed with active antiroll tanks as a means of preventing large amplitude roll motions. A robust state feedback controller for the pumps is designed that can handle model uncertainties, which arise primarily from unknown hydrodynamic loads. The approach for the controller design is a combination of sliding mode control and composite control for singularly perturbed systems, with the help of the backstepping technique. It is shown that this design can effectively control roll motions of large amplitude, including capsize prevention. Numerical simulation results for an existing fishing vessel, the twice-capsized Patti-B, are used to verify the analysis. [S0022-0434(00)02701-5]
A New Digital Algorithm for Elimination of Spillover
Authors: Utsumi M.
Published: July 2002

This paper describes a new digital algorithm for suppressing spillover-induced vibration. This algorithm can shut off the frequency components that are significantly excited by spillover with zero gain while detecting the lower modes to be controlled with gain 1 and no phase-lag, with high accuracy. Despite the noncausality of the ideal cutoff filter, a causal algorithm can be developed by utilizing the light-damping property of spillover-induced vibration. The effectiveness of the algorithm is demonstrated by computer simulation and experiment. [S0022-0434(00)01602-6]
Representing the Effect of Crystallographic Texture on the Anisotropic Performance Behavior of Rolled Aluminum Plate
Authors: Miller M. P. , Barton N. R.
Published: July 2002

Rolled aluminum alloys are known to be anisotropic due to their processing histories. This paper focuses on measuring and modeling monotonic and cyclic strength anisotropies as well as the associated anisotropy of the elastic/elastic-plastic transition of a commercially-available rolled plate product. Monotonic tension tests were conducted on specimens in the rolling plane of 25.4 mm thick AA 7075-T6 plate taken at various angles to the rolling direction (RD). Fully-reversed tension/compression cyclic experiments were also conducted. As expected, we found significant anisotropy in the back-extrapolated yield strength. We also found that the character of the elastic/elastic-plastic transition (knee of the curve) to be dependent on the orientation of the loading axis. The tests performed in RD and TD (transverse direction) had relatively sharp transitions compared to the test data from other orientations. We found the cyclic response of the material to reflect the monotonic anisotropy. The material response reached cyclic stability in 10 cycles or less with very little cyclic hardening or softening observed. For this reason, we focused our modeling effort on predicting the monotonic response. Reckoning that the primary source of anisotropy in the rolled plate is the processing-induced crystallographic texture, we employed the experimentally-measured texture of the undeformed plate material in continuum slip polycrystal plasticity model simulations of the monotonic experiments. Three types of simulations were conducted, upper and lower bound analyses and a finite element calculation that associates an element with each crystal in the aggregate. We found that all three analyses predicted anisotropy of the back-extrapolated yield strength and post-yield behavior with varying degrees of success in correlating the experimental data. In general, the upper and lower bound models predicted larger and smaller differences in the back-extrapolated yield strength, respectively, than was observed in the data. The finite element results resembled those of the upper bound when initially cubic elements were employed. We found that by employing an element shape that was more consistent with typical rolling microstructure, we were able to improve the finite element prediction significantly. The anisotropy of the elastic/elastic-plastic transition predicted by each model was also different in character. The lower bound predicted sharper transitions than the upper bound model, capturing the shape of the knee for the RD and TD data but failing to capture the other orientations. In contrast, the upper bound model predicted relatively long transitions for all orientations. As with the upper bound, the FEM calculation predicted gentle transitions with less transition anisotropy predicted than that of the upper bound. [S0094-4289(00)00201-2]
The Potential for LNG as a Railroad Fuel in the U.S.
Authors: Fritz S. G.
Published: July 2002

Freight railroad operations in the United States represent a substantial opportunity for liquified natural gas (LNG) to displace diesel fuel. With the promise of achieving an overwhelming economic advantage over diesel fuel, this paper presents some discussion to the question, “Why is the application of LNG for railroad use in the U.S. moving so slowly?” A brief overview of the freight railroad operations in the U.S. is given, along with a summary of several railroad LNG demonstration projects. U.S. Environmental Protection Agency and California Air Resources Board exhaust emission regulations may cause the railroad industry to move from small-scale LNG demonstration projects to using LNG as a primary freight railroad transportation fuel in selected regions or route-specific applications. [S0742-4795(00)01901-3]
A Comparative Study of Two Practical Methods for Estimating the
Hydrodynamic Loads and Motions of a Semi-Submersible
Authors: Söylemez M. , Atlar M.
Published: July 2002

This article presents a comparative study of two practical methods for the estimation of the hydrodynamic loads and motion responses of a semisubmersible to demonstrate some important shortcomings inherent with each method. These methods are: Morison’s equation with constant hydrodynamic coefficients, and panel method based on two-dimensional (2-D) Green’s function integral equation technique. The article includes a brief formulation of each method dedicated to a twin-hull semisubmersible and presents the results of the comparative calculations with each method performed on a twin-circular hull of eight-column semisubmersible model. The results of the calculations are discussed by emphasizing relative importance of these shortcomings and recommendations are made to the designers to be aware of them in the use of both methods. [S0892-7219(00)00401-5]