bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of Asperity Interactions in Elastic-Plastic Contact of Rough Surfaces
Authors: Zhao Yongwu , Chang L.
Published: July 2002

This paper presents a micro-contact model incorporating asperity interactions in elastic-plastic contact of rough surfaces. The effect of the asperity interactions on the local deformation behavior of a given micro-contact is first modeled based on the Saint-Venant’s Principle and Love’s Formula. The local contact interference is related in closed form to the local contact load, the global mean pressure and material parameters. This micro-contact model equation is then integrated into the elastic-plastic contact model developed in Zhao et al. (2000) to allow the asperity interactions and plastic deformation to be considered simultaneously. The effects of the asperity interactions on the mean surface separation, the real area of contact and the redistribution of the contact load among contacting asperities of different heights are studied. The results show that the asperity interactions can significantly affect the mean surface separation and micro-contact load redistribution. The results also reveal that the effect of asperity interactions can be largely cancelled out by the effect of asperity plastic deformation.
A Strain-Based Formulation for the Coupled Viscoelastic/Damage Behavior
Authors: Abdel-Tawab K. , Weitsman Y. J.
Published: July 2002

A strain-based thermodynamics framework is proposed for modeling the continuum damage behavior of viscoelastic materials. Damage is represented by an internal state variable in the form of a symmetric second rank tensor. The effect of damage on the constitutive behavior is introduced through direct coupling between the damage variable and the viscoelastic internal state variables. This approach accounts for time-dependent damage as well as damage-induced changes in material symmetry. Also, damage evolution is modeled by employing the concept of damage surfaces. This work is motivated by experimental observations of the response of swirl-mat and random chopped fiber mat polymeric composites where viscoelastic creep was accompanied by a multitude of fiber/matrix interfacial cracks.
Frequency Dependence of Dynamic Curvature Effects on Flow Through Coronary Arteries
Authors: Moore, James E. , Weydahl Erlend S. , Santamarina Aland
Published: July 2002

The flow through a curved tube model of a coronary artery was investigated computationally to determine the importance of time-varying curvature on flow patterns that have been associated with the development of atherosclerosis. The entry to the tube was fixed while the radius of curvature varied sinusoidally in time at a frequency of 1 or 5 Hz. Angiographic data from other studies suggest that the radius of curvature waveform contains significant spectral content up to 6 Hz. The overall flow patterns were similar to those observed in stationary curved tubes; velocity profile skewed toward the outer wall, secondary flow patterns, etc. The effects of time-varying curvature on the changes in wall shear rate were expressed by normalizing the wall shear rate amplitude with the shear rate calculated at the static mean radius of curvature. It was found that the wall shear rate varied as much as 94 percent of the mean wall shear rate at the mid wall of curvature for a mean curvature ratio of 0.08 and a 50 percent change in radius of curvature. The effects of 5 Hz deformation were not well predicted by a quasi-static approach. The maximum values of the normalized inner wall shear rate amplitude were found to scale well with a dimensionless parameter equivalent to the product of the mean curvature ratio (δ), normalized change in radius of curvature (ε), and a Womersley parameter (α). This parameter was less successful at predicting the amplitudes elsewhere in the tube, thus additional studies are necessary. The mean wall shear rate was well predicted with a static geometry. These results indicate that dynamic curvature plays an important role in determining the inner wall shear rates in coronary arteries that are subjected to deformation levels of εδα>0.05. The effects were not always predictable with a quasi-static approach. These results provide guidelines for constructing more realistic models of coronary artery flow for atherogenesis research.
Transient Green’s Function Behavior for a Prestressed Highly Elastic Half-Space
Authors: Brock L. M.
Published: July 2002

A plane-strain study of a prestressed isotropic compressible neo-Hookean half-space subjected to shear and normal surface loads is performed. The loads are either stationary and applied for an instant, or travel at an arbitrary constant speed. The transient process is viewed as the superposition of infinitesimal deformations upon large, and exact expressions for the displacements, within and upon, the half-space are obtained. These, and the associated wave patterns, demonstrate the anisotropy induced by prestress. The wave speeds themselves are sensitive to prestress; in particular, Rayleigh waves disappear beyond a critical compressive prestress. A critical tensile prestress also exists, beyond which a negative Poisson effect occurs.
Computational Modeling of Self-Excited Combustion Instabilities
Authors: Brookes S. J. , Cant R. S. , Dupere I. D. J. , Dowling A. P.
Published: July 2002

It is well known that lean premixed combustion systems potentially offer better emissions performance than conventional non-premixed designs. However, premixed combustion systems are more susceptible to combustion instabilities than non-premixed systems. Combustion instabilities (large-scale oscillations in heat release and pressure) have a deleterious effect on equipment, and also tend to decrease combustion efficiency. Designing out combustion instabilities is a difficult process and, particularly if many large-scale experiments are required, also very costly. Computational fluid dynamics (CFD) is now an established design tool in many areas of gas turbine design. However, its accuracy in the prediction of combustion instabilities is not yet proven. Unsteady heat release will generally be coupled to unsteady flow conditions within the combustor. In principle, computational fluid dynamics should be capable of modeling this coupled process. The present work assesses the ability of CFD to model self-excited combustion instabilities occurring within a model combustor. The accuracy of CFD in predicting both the onset and the nature of the instability is reported.
Mass Transfer Coefficient Measurement in Water/Oil/Gas Multiphase Flow
Authors: Wang H. , Vedapuri D. , Cai J. Y. , Hong T. , Jepson W. P.
Published: July 2002

Mass transfer studies in oil-containing multiphase flow provide fundamental knowledge towards the understanding of hydrodynamics and the subsequent effect on corrosion in pipelines. Mass transfer coefficient measurements in two-phase (oil/ferri-ferrocyanide) and three-phase (oil/ferri-ferrocyanide/nitrogen) flow using limiting current density technique were made in 10-cm-dia pipe at 25 and 75 percent oil percentage. Mass transfer coefficients in full pipe oil/water flow and slug flow were studied. A relationship is developed between the average mass transfer coefficient in full pipe flow and slug flow. The mass transfer coefficient decreased with a decrease of in-situ water cut. This was due to the existence of oil phase, which decreased the ionic mass transfer diffusion coefficient.
Mid-Wall Temperature in an Eroded Section of an Austenitic Superheater/Reheater Tube
Authors: Zarrabi Khosrow , Rose Ian
Published: July 2002

Superheater and reheater tubes in a fossil-fuelled boiler are subjected to erosion and corrosion that cause the tubes to lose their thickness in a localized manner. To avoid unscheduled tube failures due to creep damage and hence prevent large financial loss because of boiler shutdown and tube repairs, it is important to estimate creep life of these tubes. Creep life is very sensitive to metal temperature. This paper describes the development of a nondimensional parameter coined TM1*. It is shown that TM1* can be used to estimate the mid-wall metal temperature in the eroded/corroded section of tube.
A Methodology for Fatigue Prediction of Electronic Components Under Random Vibration Load
Authors: Li Ron S.
Published: July 2002

In modern automotive control modules, mechanical failures of surface mounted electronic components such as microprocessors, crystals, capacitors, transformers, inductors, and ball grid array packages, etc., are major roadblocks to design cycle time and product reliability. This paper presents a general methodology of failure analysis and fatigue prediction of these electronic components under automotive vibration environments. Mechanical performance of these packages is studied through finite element modeling approach for given vibration environments in automotive application. The vibration simulation provides system characteristics such as modal shapes and transfer functions, and dynamic responses including displacements, accelerations, and stresses. The system level model is correlated through vibration experiments. Using the results of vibration simulation, fatigue life is predicted based on cumulative damage analysis and material durability information. Detailed model of solder/lead joints is built to correlate the system level model and obtain solder stresses. Predicted failure mechanism of the leads agrees with the experiment observation. On the test vehicle with multiple components, one of the 160-pin gull-wing lead plastic quad flat packages was chosen as an example to illustrate the approach of failure analysis and fatigue life prediction.
Hemodynamic Factors at the Distal End-to-Side Anastomosis of a Bypass Graft With Different POS:DOS Flow Ratios
Authors: Li Xue-Mei , Rittgers Stanley E.
Published: July 2002

A pulsatile flow in vitro model of the distal end-to-side anastomosis of an arterial bypass graft was used to examine the effects that different flow ratios between the proximal outlet segment (POS) and the distal outlet segment (DOS) have on the flow patterns and the distributions of hemodynamic factors in the anastomosis. Amberlite particles were tracked by flow visualization to determine overall flow patterns and velocity measurements were made with Laser Doppler anemometry (LDA) to obtain detailed hemodynamic factors along the artery floor and the graft hood regions. These factors included wall shear stress (WSS), spatial wall shear stress gradient (WSSG), and oscillatory index (OSI). Statistical analysis was used to compare these hemodynamic factors between cases having different POS:DOS flow ratios (Case 1—0:100, Case 2—25:75, Case 3—50:50). The results showed that changes in POS:DOS flow ratios had a great influence on the flow patterns in the anastomosis. With an increase in proximal outlet flow, the range of location of the stagnation point along the artery floor decreased, while the extent of flow separation along the graft hood increased. The statistical results showed that there were significant differences p<0.05 for the mean WSS between cases along the graft hood, but no significant differences were detected along the artery floor. There were no significant differences for the spatial WSSG along both the artery floor and the graft hood. However, there were significant differences p<0.05 in the mean OSI between Cases 1 and 2 and between Cases 1 and 3 both along the artery floor and along the graft hood. Comparing these mechanical factors with histological findings of intimal hyperplasia formation obtained by previous canine studies, the results of the statistical analysis suggest that regions exposed to a combination of low mean WSS and high OSI may be most prone to the formation of intimal hyperplasia.
Application of Design Axioms for Glass Bulb Design and Software Development for Design Automation
Authors: Do Sung-Hee , Park Gyung-Jin
Published: July 2002

The automation concept is being applied to many areas as the automation system in the manufacturing field works more efficiently. Automation of the design process is also very important for the reduction of the entire engineering cost, and can be achieved by an excellent design process and software development. Design axioms have been announced as a general theoretical framework for all design fields. Application of the design axioms is investigated, and automation is obtained by computer programs. The design process can be analyzed and newly defined to satisfy the axioms. A software system can be designed according to the newly defined design process. In this research, a conventional design process for a TV glass design has been improved by an axiomatic approach, and a software system is designed for the automation of the design process. It is found that the conventional process is coupled, and the coupling causes inefficiencies. A new process is established by the application of axioms. A software design is conducted based on the new process and software development is carried out according to the software design. The developed software is exploited well in the real design.
Performance Characteristics of a Centrifugal Pump Impeller With Running Tip Clearance Pumping Solid-Liquid Mixtures
Authors: Engin Tahsin , Gur Mesut
Published: July 2002

This paper presents extensive results on the performance of an unshrouded centrifugal pump impeller handling solid-liquid mixtures. The effect of the clearance between the impeller tip and the casing and of the solid concentration, density and mean diameter on the pump performance characteristics is investigated. The results are discussed and utilized, together with data available in the literature, to establish a correlation allowing the prediction of the head reduction factor for shrouded/unshrouded impeller centrifugal pumps handling solid-liquid mixtures. The predictions made with the proposed correlation show a better agreement with experimental results than previous ones.
Detecting and Correcting Cylinder Imbalance in Direct Injection Engines
Authors: van Nieuwstadt M. J. , Kolmanovsky I. V.
Published: July 2002

Modern direct injection engines feature high pressure fuel injection systems that are required to control the fuel quantity very accurately. Due to limited manufacturing accuracy these systems can benefit from an on-line adaptation scheme that compensates for injector variability. Since cylinder imbalance affects many measurable signals, different sensors and algorithms can be used to equalize torque production by the cylinders. This paper compares several adaptation schemes that use different sensors. The algorithms are evaluated on a cylinder-by-cylinder simulation model of a direct injection high speed diesel engine. A proof of stability and experimental results are reported as well.
Intimal Hyperplasia and Wall Shear in Arterial Bypass Graft Distal Anastomoses: An In Vivo Model Study
Authors: Keynton Robert S. , Evancho Mary M. , Sims Rick L. , Rodway Nancy V. , Gobin Andrea , Rittgers Stanley E.
Published: July 2002

The observation of intimal hyperplasia at bypass graft anastomoses has suggested a potential interaction between local hemodynamics and vascular wall response. Wall shear has been particularly implicated because of its known effects upon the endothelium of normal vessels and, thus, was examined as to its possible role in the development of intimal hyperplasia in arterial bypass graft distal anastomoses. Tapered (4–7 mm I.D.) e-PTFE synthetic grafts 6 cm long were placed as bilateral carotid artery bypasses in six adult, mongrel dogs weighing between 25 and 30 kg with distal anastomotic graft-to-artery diameter ratios (DR) of either 1.0 or 1.5. Immediately following implantation, simultaneous axial velocity measurements were made in the toe and artery floor regions in the plane of the anastomosis at radial increments of 0.35 mm, 0.70 mm, and 1.05 mm using a specially designed 20 MHz triple crystal ultrasonic wall shear rate transducer. Mean, peak, and pulse amplitude wall shear rates (WSRs), their absolute values, the spatial and temporal wall shear stress gradients (WSSG), and the oscillatory shear index (OSI) were computed from these velocity measurements. All grafts were harvested after 12 weeks implantation and measurements of the degree of intimal hyperplasia (IH) were made along the toe region and the artery floor of the host artery in 1 mm increments. While some IH occurred along the toe region (8.35±23.1 μm) and was significantly different between DR groups p<0.003, the greatest amount occurred along the artery floor (81.6±106.5 μm, mean±S.D.) p<0.001 although no significant differences were found between DR groups. Linear regressions were performed on the paired IH and mean, peak, and pulse amplitude WSR data as well as the absolute mean, peak, and pulse amplitude WSR data from all grafts. The mean and absolute mean WSRs showed a modest correlation with IH (r=−0.406 and −0.370, respectively) with further improvements seen (r=−0.482 and −0.445, respectively) when using an exponential relationship. The overall best correlation was seen against an exponential function of the OSI r=0.600. Although these correlation coefficients were not high, they were found to be statistically significant as evidenced by the large F-statistic obtained. Finally, it was observed that over 75 percent of the IH occurred at or below a mean WSR value of 100 s−1 while approximately 92 percent of the IH occurred at or below a mean WSR equal to one-half that of the native artery. Therefore, while not being the only factor involved, wall shear (and in particular, oscillatory wall shear) appears to provide a stimulus for the development of anastomotic intimal hyperplasia.
Viscoplastic Constitutive Modeling of Anisotropic Damage Under Nonproportional Loading
Authors: Chow C. L. , Yang X. J. , Chu Edmund
Published: July 2002

Based on the theory of damage mechanics, a viscoplastic constitutive modeling of anisotropic damage for the prediction of forming limit curve (FLC) is developed. The model takes into account the effect of rotation of principal damage coordinates on the deformation and damage behaviors. With the aid of the damage viscoplastic potential, the damage evolution equations are established. Based on a proposed damage criterion for localized necking, the model is employed to predict the FLC of aluminum 6111-T4 sheet alloy. The predicted results agree well with those determined experimentally.
Effect of Temperature on Thermoelastic Instability in Thin Disks
Authors: Davis Coby L. , Krousgrill Charles M. , Sadeghi Farshid
Published: July 2002

A model of a thin annular plate sliding against an elastic foundation was developed and used to study thermoelastic instability (TEI) in clutches. The analysis examines the stability of the quasi-steady state solution of the governing equations by considering non-axisymmetric perturbations. The results indicate that above critical values of temperature and sliding speed the response of the plate becomes unstable and exhibits large deformations. Two mechanisms account for this behavior: thermal buckling and bending. It is shown that a conservative approximation of the stability boundaries can be constructed by computing only two points on the stability curve. The boundary between stable and unstable behavior depends on the material properties, geometry, and boundary conditions. The model was used to conduct a parametric study which indicates that stability of the sliding system can be improved by reducing the sliding speed, decreasing the modulus of elasticity of the plate, increasing the thermal conductivity, or increasing the thickness. In addition, for a range of sliding speeds, increasing the stiffness of the friction material improves the stability of the system. For speeds outside this range, increasing the stiffness makes the system less stable.
Use of Electrostatic Charge Monitoring for Early Detection of Adhesive Wear in Oil Lubricated Contacts
Authors: Morris S. , Wood R. J. K. , Harvey T. J. , Powrie H. E. G.
Published: July 2002

Electrostatic charge sensing technology has been used to monitor adhesive wear in oil lubricated contacts. Previous work in this area demonstrated that “precursor” charge events may be detected prior to the onset of scuffing. Possible charging mechanisms associated with the precursor events were identified as tribocharging, surface charge variation, exo-emissions and debris generation. This paper discusses the proposed charging mechanisms and details a series of investigative tests using an adapted pin-on-disc (PoD) rig. The PoD tests focused on surface charge variation effects and were of two types, non-contact, where different materials were inserted in the disc, and controlled scuffing tests.
Direct Observations of the Chip-Tool Interface in the Low Speed Cutting of Pure Metals
Authors: Madhavan V. , Chandrasekar S. , Farris T. N.
Published: July 2002

An experimental study of the chip-tool interface and its evolution in the low speed cutting of metals has been carried out. Specially prepared transparent glass and sapphire tools have been used to cut commercially pure metals such as lead, aluminum and copper. The chip-tool interface has been observed in situ using optical microscopy and recorded on film and video tape. By observing the motion of inhomogeneities in the chip, and profilometry of the chip and tool surfaces, it has been established that there is intimate sliding contact between the chip and the tool at and near the cutting edge. Farther away from the cutting edge and close to the end of the chip-tool contact, metal transfer and sticking are observed between the chip and tool surfaces. It has been shown that metal deposition on the rake face initially occurs near the point at which the chip curls out of contact with the tool and progressively extends outward and away from the cutting edge in conjunction with an increase in the length of contact as cutting progresses. The sticking and sliding zones are unchanged when these pure metals are machined with tungsten carbide tools.
Predictions of a Turbulent Separated Flow Using Commercial CFD Codes
Authors: Iaccarino Gianluca
Published: July 2002

Numerical simulations of the turbulent flow in an asymmetric two-dimensional diffuser are carried out using three commercial CFD codes: CFX, Fluent, and Star-CD. A low-Reynolds number k-ε model with damping functions and the four-equation v′2¯−f model are used; the first one is available as a standard feature in all the codes, the v′2¯−f model was implemented using the User Defined Routines. The flow features a large recirculating zone due to the adverse pressure gradient in the diffuser; the v′2¯−f predictions agree very well with the experiments both for the mean velocity and the turbulent kinetic energy. The length of the separation bubble is also computed within 6 percent of the measured value. The k-ε calculations do not show any recirculation and the agreement with the measurements is very poor. The three codes employed show very similar characteristics in terms of convergence and accuracy; in particular, the results obtained using the v′2¯−f are consistent in all the codes, while appreciable differences are obtained when the k-ε is employed.
Reverse Flow as a Possible Mechanism for Cavitation Pressure Build-up in a Submerged Journal Bearing
Authors: Groper M. , Etsion I.
Published: July 2002

An experimentally observed reverse flow phenomenon at the end tip of the cavitation zone of a submerged journal bearing is modeled and theoretically investigated. The shape of the cavity, the nature of the reverse flow and the pressure distribution in the bearing are calculated in an attempt to understand previous experimental observations of pressure build up in the cavitation zone. A comparison with the available experimental results reveals that the cavitation shape, the behavior of the reverse flow and the pressure distribution are fairly well predicted by the present model. The reverse flow mechanism is indeed capable to generate the level of the experimentally measured pressures, particularly towards the end of the cavitation zone.
An Experimental Analysis of Misalignment Effects on Hydrodynamic Plain Journal Bearing Performances
Authors: Bouyer J. , Fillon M.
Published: July 2002

The present study deals with the experimental determination of the performance of a 100 mm diameter plain journal bearing submitted to a misalignment torque. Hydrodynamic pressure and temperature fields in the mid-plane of the bearing, temperatures in two axial directions, oil flow rate, and minimum film thickness, were all measured for various operating conditions and misalignment torques. Tests were carried out for rotational speeds ranging from 1500 to 4000 rpm with a maximum static load of 9000 N and a misalignment torque varying from 0 to 70 N.m. The bearing performances were greatly affected by the misalignment. The maximum pressure in the mid-plane decreased by 20 percent for the largest misalignment torque while the minimum film thickness was reduced by 80 percent. The misalignment caused more significant changes in bearing performance when the rotational speed or load was low. The hydrodynamic effects were then relatively small and the bearing offered less resistance to the misalignment.
Blade Dynamic Stall Vortex Kinematics for a Horizontal Axis Wind Turbine in Yawed Conditions*
Authors: Schreck Scott J. , Robinson Michael C. , Hand M. Maureen , Simms David A.
Published: July 2002

Horizontal axis wind turbines routinely suffer significant time varying aerodynamic loads that adversely impact structures, mechanical components, and power production. As lighter and more flexible wind turbines are designed to reduce overall cost of energy, greater accuracy and reliability will become even more crucial in future aerodynamics models. However, to render calculations tractable, current modeling approaches admit various approximations that can degrade model predictive accuracy. To help understand the impact of these modeling approximations and improve future models, the current effort seeks to document and comprehend the vortex kinematics for three-dimensional, unsteady, vortex dominated flows occurring on horizontal axis wind turbine blades during non-zero yaw conditions. To experimentally characterize these flows, the National Renewable Energy Laboratory Unsteady Aerodynamics Experiment turbine was erected in the NASA Ames 80 ft×120 ft wind tunnel. Then, under strictly-controlled inflow conditions, turbine blade surface pressures and local inflow velocities were acquired at multiple radial locations. Surface pressure histories and normal force records were used to characterize dynamic stall vortex kinematics and normal forces. Stall vortices occupied approximately two-thirds of the aerodynamically active blade span and persisted for nearly one-fourth of the blade rotation cycle. Stall vortex convection varied dramatically along the blade radius, yielding pronounced dynamic stall vortex deformation. Analysis of these data revealed systematic alterations to vortex kinematics due to changes in test section speed, yaw error, and blade span location.
A Note on the Computation of the Euler Parameters
Authors: Johansson Lars
Published: July 2002

This paper is concerned with the integration of the differential equations for the Euler parameters, for the purpose of describing the orientation of a rigid body. This can be done using standard methods, but in some cases, such as in the presence of impulsive forces, the angular velocities are not continuous and methods based on high order continuity are not appropriate. In this paper, the use of the closed-form solution for piecewise constant angular velocity as the basis for a computational algorithm is studied. It is seen that if this solution is implemented in a leapfrog manner a method with second-order accuracy is obtained in the smooth case, while this method also makes sense in the discontinuous case.
Moving Loads on an Elastic Half-Plane With Hysteretic Damping
Authors: Verruijt A. , Co´rdova C. Cornejo
Published: July 2002

A closed-form solution is presented for the problem of a moving point load on an elastic half-plane with hysteretic damping. The problem has been studied in order to investigate the dynamic amplification of stresses and displacements if the velocity of the load approaches the Rayleigh wave velocity or the shear wave velocity in the elastic medium. This is relevant for the construction of high speed railway lines on relatively soft soils. Hysteretic damping is introduced as pseudo-viscous damping, assuming that the damping in a full cycle of loading and unloading is independent of the frequency.
Control Systems for Ultra-High Rise Elevators1
Authors: Venkatesh S. R. , Cho Y. M.
Published: July 2002

We present a scalable and tunable control design for controlling elevator vertical motion for ultra high-rise buildings. Scalability is desirable to enable customization to any hoistway while tunability enables periodic adjustments to normal wear and tear. We accomplish these objectives by first validating a scalable lumped parameter model that is based on a few prominent features in the vertical dynamics. A tunable controller based only on these features is developed and through simulations we show that the controller meets a set of standardized elevator performance tests while maintaining global exponential stability.
Feature Based Shape Similarity Measurement for Retrieval of Mechanical Parts
Authors: Ramesh Madhumati , Yip-Hoi Derek , Dutta Debasish
Published: July 2002

Exploiting shape similarities amongst parts for applications such as variant process planning is well known in the manufacturing industry. This particular application requires a mechanism for retrieval of similar parts from a part database which in turn requires a method for shape similarity measurement. In this paper, such a method is presented. First, the part is decomposed into simpler shapes resembling machining features. The decomposition method makes use of primitives to generate the shapes directly unlike previous methods in which the shapes are produced by combining minimal cells. Next, part characteristics that capture the spatial and dimensional relationships amongst features are used to measure the similarity. These characteristics are relevant to machining and they complement the characteristics such as feature type and feature intersections that are used by the previous shape comparison techniques. Implementation and examples are also included.
Nonlinear Influence of Effective Lead Angle in Turning Process Stability
Authors: Vogler Michael P. , DeVor Richard E. , Kapoor Shiv G.
Published: July 2002

An analytical method for stability prediction incorporating the nonlinear influence of the effective lead angle in turning is proposed and validated. It is shown that as the effective lead angle changes, due to depth of cut variations on a nose radiused cutting insert, different structural modes are excited, resulting in different stability results. Experiments have been performed on a two degree-of-freedom system representative of the turning of long, slender bars. It is shown that chatter may be present at low depths of cut, typically less than the nose radius of the insert. The proposed model is also capable of predicting the chatter present at larger depths of cut that is typically reported in literature.
Study of Wake-Blade Interactions in a Transonic Compressor Using Flow Visualization and DPIV
Authors: Estevadeordal J. , Gogineni S. , Goss L. , Copenhaver W. , Gorrell S.
Published: July 2002

Flow-field interactions are studied in a high-through-flow, axial-flow transonic compressor using Digital Particle Image Velocimetry (DPIV). Measurement of instantaneous velocities in two-dimensional (2D) planes in the main flow direction allows characterization of the unsteadiness of spatial structures from an upstream blade row and their interaction with the downstream rotor. The measurement system is specially designed for a large transonic environment, which introduces conditions that differ from those generally encountered by traditional DPIV systems. Viewing windows on the compressor housing are used to allow optical access, and the design of a special optical probe permits laser-sheet delivery through one of the wake generators (WG). The system is synchronized with the blade passage and is remotely monitored and controlled. Through flow visualization and instantaneous and ensemble-averaged quantities, it clearly captures the interactions of the wake with the potential field of the rotor leading edge (LE) and its bow shock, vortex shedding, vortex-blade synchronization, wake chopping, and boundary-layer flow at the housing for several configurations.
The Modulus of Toughness of Urinary Calculi
Authors: Wang Shyh-Jen , Yip Ming-Chuen , Hsu Yen-Shen , Lai Kun-Guo , Wang Shyh-Yau
Published: July 2002

To improve the efficacy of extracorporeal shock wave lithotripsy (ESWL) treatment, it is desirable to identify the physical properties of urinary calculi could offer direct correlation with their fragilities during ESWL and thus could be used to guide treatment procedures for more effective stone fragmentation. Thirty stone specimens removed surgically were compressed by an axial testing system to measure the compressive strength and trace the stress-strain curve. Image analysis software SigmaScan (Jandel Co.) was used to calculate the area under the stress-strain curve, the modulus of toughness, for each stone. The values of compressive strength measured were similar to those reported by other researchers. The modulus of toughness of urinary calculi correlates with clinical representation of the stone fragility during ESWL. The modulus of toughness could be an index to evaluate the physical property of urinary calculi that could be used to guide treatment procedures for more effective stone fragmentation.
Prediction of Forming Limit Diagram Based on Damage Coupled
Kinematic-Isotropic Hardening Model Under Nonproportional Loading
Authors: Chow C. L. , Yang X. J. , Chu E.
Published: July 2002

Based on the theory of damage mechanics, an anisotropic damage coupled mixed isotropic-kinematic hardening plastic model for the prediction of forming limit diagram (FLD) is developed. The model includes the formulation of nonlinear anisotropic kinematic hardening. For the prediction of limit strains under nonproportional loading, a damage criterion for localized necking of sheet metals subjected to complex strain history is proposed. The model is employed to predict the FLDs of AL6111-T4 alloy. The predicted results agree well with those determined experimentally.
Diagnosability Analysis of Multi-Station Manufacturing Processes
Authors: Ding Yu , Shi Jianjun , Ceglarek Dariusz
Published: July 2002

Variation propagation in a multi-station manufacturing process (MMP) is described by the theory of “Stream of Variation.” Given that the measurements are obtained via certain sensor distribution scheme, the problem of whether the stream of variation of an MMP is diagnosable is of great interest to both academia and industry. We present a comprehensive study of the diagnosability of MMPs in this paper. It is based on the state space model and is parallel to the concept of observability in control theory. Analogous to the observability matrix and index, the diagnosability matrix and index are first defined and then derived for MMP systems. The result of diagnosability study is applied to the evaluation of sensor distribution strategy. It can also be used as the basis to develop an optimal sensor distribution algorithm. An example of a three-station assembly process with multi-fixture layouts is presented to illustrate the methodology.
Nanosecond Laser Repair of Adhered MEMS Structures
Authors: Rogers James W. , Phinney Leslie M.
Published: July 2002

Due to the small component sizes in modern microdevices, surface forces can create undesirable adhesion between microstructures, which is referred to as stiction. The current study uses a 100 ns, 1064 nm, Nd:YAG laser to repair polycrystalline silicon microcantilevers stuck to the underlying substrate. The results show that a Nd:YAG, 1064 nm laser is capable of repairing failed microstructures with yields exceeding those reported in earlier studies. Yields of 100 percent for cantilevers up to 1 mm in length were demonstrated for several laser operating conditions. The yields increase strongly with increased laser fluence and increase slightly with longer exposure times.
An Argument for Enhancement of the Current Inlet Distortion Ground
Test Practice for Aircraft Gas Turbine Engines
Authors: Davis Milt , Hale Alan , Beale Dave
Published: July 2002

The current high-performance aircraft development programs, and the trends in research and development activities suggest a rapidly increasing level of aircraft subsystem integration, particularly between the airframe/inlet and the propulsion system. Traditionally, these subsystems have been designed, analyzed, and tested as isolated systems. The interaction between the subsystems is modeled primarily through evaluating inlet distortion in an inlet test and simulating this distortion in engine tests via screens or similar devices. For the current test methodology, the environment that is supplied by the inlet is simulated by the imposition of total pressure profiles at the aerodynamic interface plane (AIP). Unsteady or transient variation in total pressure is generally not considered to be important. In addition, angular flow, commonly called swirl, is also not considered important enough to be simulated. In the current paper, an overview of current techniques for inlet performance, distortion characterization, and engine distortion testing is presented. A numerical study was conducted on a single high-speed rotor to qualify potential effects on stability and performance and to support the concept that dynamic distortion and swirl may have large enough effects to affect the experimentally determined stability limit. This paper reports a numerical investigation using a 3-D compression system simulation that supports the enhancement of the existing methodology to include the effects of time-dependent distortion and swirl effects. Based upon both experimental and numerical evidence, AEDC has embarked on efforts to develop inlet simulator technologies directed toward future airframe-propulsion integration requirements. This paper presents issues that require advancements in the simulation of inlet distortion techniques for direct-connect turbine engine tests.
Finite Element Investigation of Quasi-Static Crack Growth in Functionally Graded Materials Using a Novel Cohesive Zone Fracture Model
Authors: Jin Z.-H. , Paulino G. H. , Dodds, R. H.
Published: July 2002

This work studies mode I crack growth in ceramic/metal functionally graded materials (FGMs) using three-dimensional interface-cohesive elements based upon a new phenomenological cohesive fracture model. The local separation energies and peak tractions for the metal and ceramic constituents govern the cohesive fracture process. The model formulation introduces two cohesive gradation parameters to control the transition of fracture behavior between the constituents. Numerical values of volume fractions for the constituents specified at nodes of the finite element model set the spatial gradation of material properties with standard isoparametric interpolations inside interface elements and background solid elements to define pointwise material property values. The paper describes applications of the cohesive fracture model and computational scheme to analyze crack growth in compact tension, C(T), and single-edge notch bend, SE(B), specimens with material properties characteristic of a TiB/Ti FGM. Young’s modulus and Poisson’s ratio of the background solid material are determined using a self-consistent method (the background material remains linear elastic). The numerical studies demonstrate that the load to cause crack extension in the FGM compares to that for the metal and that crack growth response varies strongly with values of the cohesive gradation parameter for the metal. These results suggest the potential to calibrate the value of this parameter by matching the predicted and measured crack growth response in standard fracture mechanics specimens.
A Modeling Study of Partial ACL Injury: Simulated KT-2000 Arthrometer Tests
Authors: Liu Wen , Maitland Murray E. , Bell G. Douglas
Published: July 2002

A partial ACL injury may involve different levels of fiber disruption, or fibers may sustain microscopic changes in their structure without gross disruption, resulting in a change in ligament function. The effect of partial ACL tears on the mechanical and functional stability of the knee has not been well documented, in part because of diagnostic difficulties. A computer model of the knee in the sagittal plane was used in this study to simulate tests using the KT-2000 Knee Arthrometer, which quantifies Lachman’s test for ACL injury. A variety of partial ACL anterior and posterior bundle injuries were simulated. Anterior and posterior bundle injuries were subdivided into four different simulated injury levels: mild (one-half tear of the bundle), moderate (complete tear of the bundle), severe (complete tear of the bundle and tear of one-half of the other bundle), and more severe (severe injury plus an additional elongation of the other bundle represented by 5% increases of its initial strain). Force-displacement results obtained from simulated KT-2000 knee arthrometer tests depended on the level of injury. Mild and moderate injuries produced only small change in the anterior tibial translation—at different force levels. Severe injury produced increased anterior tibial translation depending on which bundle was completely ruptured. The compliance index defined as the ratio of the displacement and the force within 68 N and 90 N anterior drawer forces, the stiffness, and the rate of change of stiffness of the anterior force-displacement were found to be better at predicting partial ACL ruptures than simple differences in anterior tibial translation. It was possible in the model results to discriminate knees with various levels of partial ACL injuries using the first and second derivatives of the force-displacement curve.
One-Step-Ahead Adaptive Control for Gas Turbine Power Plants
Authors: Camporeale S. M. , Dambrosio and L. , Fortunato B.
Published: July 2002

The feasibility of the application of One-Step-Ahead Adaptive (OSAA) Control technique to a gas turbine power plant is investigated. The OSAA technique is a control algorithm especially suitable for nonlinear and time-varying systems. This technique uses the least square algorithm to estimate in real-time a linear model of the controlled system and uses the estimated linear model to evaluate the feedback control variables. The proposed technique allows to control the gas turbine power plant in a wide range of electric loads due to its intrinsic adaptive capabilities. Moreover, the OSAA control does not require the knowledge of the dynamic characteristics (e.g., state space systems or transfer functions) in order to design the control system. The OSAA control system has been applied to a single shaft gas turbine power plant, which is numerically simulated. The proposed control technique has been tested both in Single-Input Single Output (SISO) mode and in Multi-Input Multi-Output (MIMO) mode. Starting from a steady-state condition, the power plant has been supposed to undergo a step reduction of the electric load. The results show that the OSAA control technique effectively counteracts the load reduction with limited overshoots in the controlled variables and, introducing an integral correction with a negligible static error.
Nonlinear Force/Pressure Tracking of an Electro-Hydraulic Actuator1
Authors: Liu Rui , Alleyne Andrew
Published: July 2002

In this paper, a Lyapunov-based control algorithm is developed for the force/pressure tracking control of an electro-hydraulic actuator. The controller relies on an accurate model of the system. To compensate for the parameter uncertainties, a standard parameter adaptation based on Lyapunov analysis is applied. The control law is coupled with the adaptation scheme and applied to an experimental system. Friction modeling and compensation for pressure tracking are discussed and experimental results shown. The results show that the nonlinear control algorithm together with the adaptation scheme gives a good performance for the specified task. [S0022-0434(00)00501-3]
Analysis of Combustion in Diesel Engines Fueled by Directly Injected Natural Gas
Authors: Hill P. G. , Douville B.
Published: July 2002

A single-cylinder two-stroke (DDC 1-71) diesel engine has been fueled with natural gas directly injected at high pressure into the engine cylinder. Prior to injection of the natural gas, a quantity of diesel fuel is injected into the cylinder (from the same injector) to provide for gas ignition. Tests have been conducted at medium load and speed over a wide range of injection timing, and with both conventional diesel and gas/diesel operation. With natural gas fueling, significant reduction in nitrogen oxide emissions have been measured without significant loss in efficiency, relative to conventional diesel operation. Using measurements of cylinder pressure development, a new method of combustion analysis has been used to estimate mass burning rate, burned gas temperature, and rate of nitrogen oxide (NO) generation. The method uses a nonlinear regression technique to determine the distribution with crank angle of the cylinder heat loss rate. The method assumes that NO formation takes place within one turbulent mixing time following combustion of each fuel-air increment. Comparison of measured and calculated NO concentration in the exhaust over the whole range of injection timing shows that for both conventional diesel and gas/diesel operation the effective turbulent mixing period is equivalent to 4 degrees of crank angle at 1250 RPM. The results demonstrate that a mass burned method can be used to infer cylinder temperature distributions and NO formation rate as well as the progress of combustion. [S0742-4795(00)02101-3]
Quantitative Visualization of the Flow in a Centrifugal Pump With Diffuser Vanes—II: Addressing Passage-Averaged and Large-Eddy Simulation Modeling Issues in Turbomachinery Flows
Authors: Sinha Manish , Katz Joseph , Meneveau Charles
Published: July 2002

The present paper addresses two basic modeling problems of the flow in turbomachines. For simulation of flows within multistage turbomachinery, unsteady Reynolds-averaged Navier–Stokes (RANS) of an entire series of blade rows is typically impractical. On the other hand, when performing RANS of each blade row separately one is faced with major difficulties in matching boundary conditions. A popular remedy is the “passage-averaged” approach. Unsteady effects caused by neighboring rows are averaged out over all blade orientations, but are accounted for through “deterministic” stresses, which must be modeled. To experimentally study modeling issues for deterministic stresses we use particle image velocimetry data of the flow in a centrifugal pump with a vaned diffuser that includes the flow in the impeller, the gap between the impeller and diffuser, between the diffuser vanes and within the volute downstream. The data have been presented in part A of this paper (Sinha and Katz, 1998, “Flow Structure and Turbulence of a Centrifugal Pump with a Vaned Diffuser,” Proceedings of the ASME Fluids Engineering Division, Washington, DC). Deterministic stresses are obtained from the difference between the phase-averaged and passage-averaged data, whereas the Reynolds stresses are determined from the difference between the instantaneous and phase averaged data. In agreement with previous findings, the deterministic stresses are larger than the Reynolds stresses in regions close to the interface between blade rows, and thus must be carefully accounted for in passage-averaged simulations. The Reynolds stresses are larger in regions located far from the transition region. The second series of issues involves modeling for large-eddy simulation. The measured subgrid stresses determined by spatially filtering the data are compared to eddy viscosity models and show significant discrepancies, especially in regions with separating shear layers. Backscatter of energy that persists during phase averaging is also observed. [S0098-2202(00)00901-9]