bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Phenomena and Droplet Formation During Pulsed Laser Interaction With Thin Films
Authors: Willis D. A. , Xu X.
Published: July 2002

This work investigates transport phenomena and mechanisms of droplet formation during a pulsed laser interaction with thin films. The surface of the target material is altered through material flow in the molten phase induced by a tightly focused laser energy flux. Such a process is useful for developing a laser-based micromachining technique. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the process. As with many machining techniques, debris is often generated during laser-material interaction. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exists for “clean” structures to be fabricated. The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation and droplet formation are attributed to the surface-tension-driven flow, and the recoil pressure effect plays an insignificant role in the surface topography development. [S0022-1481(00)02903-0]
On the Energy Release Rate of Fatigued Composites Subjected to Compressive Overloads
Authors: Pelegri Assimina A. , Kedlaya Diwakar N.
Published: July 2002

The behavior of delaminated graphite/epoxy composites under variable amplitude compressive loading (spectrum loading) is studied. The delamination growth is monitored in real time during fatigue tests. Different variable amplitude compressive load spectra are applied. Calculations of the energy release rate, G, as a function of the delamination length, delamination position, and applied strain during the spectrum loading are performed. Numerical simulations are based on a mixed mode fatigue growth model that is not subjected to the thin film model restrictions. The higher energy release values during the overloads were associated to the formation of intralayer and interlayer cracks on the composite specimens. [S0094-4289(00)03004-8]
Experiments on Chimney-Enhanced Free Convection From Pin-Fin Heat Sinks
Authors: Thrasher W. W. , Fisher T. S. , Torrance K. E.
Published: July 2002

Experimental results for thermal systems consisting of pin-fin heat sinks situated below chimneys are presented. System-level heat transfer and porosity optimization results are compared with previous theoretical predictions. Generally good agreement, both in trend and magnitude, exists between theory and experiment. An optimal porosity of 91 percent is observed for most conditions. Velocity measurements at the chimney exit and the effects of cold inflow are presented and discussed. [S1043-7398(00)00604-6]
Machining Cost Optimization Involving Shift and Overtime Work
Authors: Niemi Esko
Published: July 2002

Minimization of machining cost as a function of cutting speed is examined taking into account the effect of shift and overtime work. The cost minimization problem is formulated as the minimization of the total cost of machining a given number of workpieces within a given time. Different types of costs of machining and determination of cost parameters in the long run and short run are discussed. The use of both one-tool type and several-tool types is considered. Characteristics of the solutions of the problem are examined in light of examples. [S1087-1357(00)02304-2]
Unsteady Effects in Turbine Tip Clearance Flows
Authors: Prasad Anil , Wagner Joel H.
Published: July 2002

The present study is concerned with the unsteady flow field on the blade outer air seal segments of high-work turbines; these segments are installed between the blade tip and outer casing and are usually subjected to extreme heat loads. Time-resolved measurements of the unsteady pressure on the blade outer air seal are made in a low-speed turbine rig. The present measurements indicate the existence of a separation zone on the blade tip, which causes a vena contracta to form at the entrance of the tip gap. In addition, a careful comparison between the ensemble-averaged pressure measurement and the corresponding result from steady computation suggests that the pressure on the blade outer air seal can largely be described as being due to a steady flow (in the rotating frame) sweeping past a stationary probe. The ensemble deviation measurement indicates that unsteadiness (from one revolution to the next) is confined to the tip gap. [S0889-504X(00)02304-7]
Discrete Variable Structure Control for Linear Multivariable Systems
Authors: Tang Choon Yik , Misawa Eduardo A.
Published: July 2002

This paper presents a state feedback discrete variable structure controller for robust tracking of linear multivariable systems with unmatched, additive uncertainties. Extension of the controller to output feedback using a prediction observer with bias estimation is also given. It is shown that the state feedback controller guarantees attractiveness and invariance of a boundary layer, while the output feedback controller does so after a transient. Unlike existing schemes, the controllers utilize a single sliding hyperplane regardless of the number of inputs. This attribute enables the development of a procedure that admits, under minor restrictions, direct application of well-established linear control strategies in the design of tracking error dynamics. A numerical example is used to illustrate the proposed controllers. [S0022-0434(00)01904-3]
Preload Effects of a Guide Bearing on the Metal Temperature and the Shaft Vibration
Authors: Ha Hyun Cheon
Published: July 2002

Segment type vertical guide bearings are widely used for vertical rotating machinery; nevertheless, bearing problems, such as excessive vibration and temperature rise, frequently take place in the actual rotating machine. The purpose of the present work is to investigate the influence of preload effects of a segment type vertical guide bearing on the bearing metal temperature and the shaft vibration, in a hydraulic pump-turbine. Investigations have been performed not only by in-situ measurement but also by theoretical analysis. A guide bearing consists of eight pads and runs bi-directionally. Both the shaft vibration and the bearing metal temperature are very high in the non-preloaded bearing but are slight in the preloaded bearing, comparatively. Bearing metal temperature is decreased by the increase of cooling effect of the lubricant due to the preload effect. Shaft vibration is also decreased by the increase of bearing stiffness. Theoretical analysis shows that the segment type vertical guide bearing has an optimum preload ratio at which the bearing stiffness reaches a maximum value while the bearing metal temperature is minimized. Furthermore, it is found that the characteristics of shaft vibration of a Francis type hydraulic pump-turbine highly depend on the generating power.
A Nested Finite Element Methodology (NFEM) for Stress Analysis of Electronic Products—Part I: Theory and Formulation
Authors: Darbha Krishna , Dasgupta Abhijit
Published: July 2002

In this paper, the authors present a stress analysis technique based on a novel nested finite element methodology (NFEM). The NFEM is similar in concept to an earlier proposed multi-domain Rayleigh-Ritz methodology (Ling, S., 1997, “A Multi-Domain Rayleigh-Ritz Method for Thermomechanical Stress Analysis of Surface Mount Interconnects in Electronic Assemblies,” Ph.D. dissertation, Univ., of Maryland), that is based on a nested multi-field displacement assumption. The nested multi-field displacement technique may be viewed as a localized cascading of the p-type refinement in conventional finite element analysis. The concept and formulation of NFEM are presented in this paper while the application of NFEM to analyze the viscoplastic stress-state in two popular surface mount electronic interconnect styles is presented in Part II of this series. To illustrate the concept of NFEM, the formulation and results are provided for a one-dimensional viscoplastic example.
The Fiber Composite With Nonlinear Interface—Part II: Antiplane Shear
Authors: Levy A. J.
Published: July 2002

This paper treats the effective antiplane shear response of a composite consisting of fibers that interact with the matrix through nonlinear Needleman-type cohesive zones. The first paper (Part I) examines effective axial tension response. The composite cylinders representation of a representative volume element (RVE) is employed throughout. For antiplane shear loading the elastic field solution for a single composite cylinder is found in the form of a series expansion whose coefficients are governed by an infinite set of nonlinear equations. Bounds on the total potential energy and the total complementary energy of an RVE do not coincide although they are shown to differ by a term of order Oc4 where c is the fiber volume concentration. Interaction effects due to finite volume concentration, coupled with nonlinear interface characterization, are shown to precipitate instability in composite response. [S0021-8936(00)02104-8]
Metrics for Quality Assessment of a Multiobjective Design Optimization Solution Set
Authors: Wu Jin , Azarm Shapour
Published: July 2002

In this paper, several new set quality metrics are introduced that can be used to evaluate the “goodness” of an observed Pareto solution set. These metrics, which are formulated in closed-form and geometrically illustrated, include hyperarea difference, Pareto spread, accuracy of an observed Pareto frontier, number of distinct choices and cluster. The metrics should enable a designer to either monitor the quality of an observed Pareto solution set as obtained by a multiobjective optimization method, or compare the quality of observed Pareto solution sets as reported by different multiobjective optimization methods. A vibrating platform example is used to demonstrate the calculation of these metrics for an observed Pareto solution set.
High-Temperature Oxidation Behavior of 214Cr-1Mo Steel in Air—Part 1: Gain of Mass Kinetics and Characterization of the Oxide Scale
Authors: Marino Luiz , Bueno Levi O.
Published: July 2002

The oxidation behavior of 214Cr-1Mo steel was studied at 600, 700 and 800°C for a sequence of times up to 1000 h, using cylindrical specimens of the material, similar to testpieces used in high-temperature creep testing. The various samples exposed to different degrees of oxidation were investigated by optical and electron scanning microscopy and X-ray diffractometry. The oxidation rate expressed as gain of mass per area was observed to gradually slow down with the exposure time according to an approximated parabolic behavior, at all temperature levels. Multilayer oxide formation was observed to occur involving oxides with various compositions and crystallographic structures. Three main oxide layers were detected: (a) an internal one, of an FeOs˙Fe2−x.CrxO3 spinel form, containing: molybdenum; (b) an intermediate one, of an FeOs˙Fe2O3 magnetite type; (c) an external one consisting of α Fe2O3 hematite. In some instances, there was a fourth stratum formation in local spaces left by a separation between the hematite and magnetite interfaces. Each of these layers was observed to exhibit different morphological aspects, with needlelike crystals of hematite occurring at the free external surface of the material.
Thermal Performance of Integrated Plate Heat Pipe With a Heat Spreader
Authors: Take Koichiro , Webb Ralph L.
Published: July 2002

The air flow rate available for cooling of notebook computers is very limited. Thus, notebook computer manufacturers desire a “passive” cooling method. Heat pipes are typically used to transport the heat from the CPU to a forced convection, air-cooled condenser. This paper describes a passive, keyboard sized aluminum Integrated Plate Heat Pipe (IP-HP) that has been developed for notebook computers. Analysis was performed to estimate the several thermal resistances in the heat pipe, including the effect of the vapor pressure drop. The modified design using a heat spreader at the evaporator significantly reduces the heat pipe resistance. Further work was done to evaluate the thermal contact resistance at the IP-HP/CPU interface. Test results show that the IP-HP can reject 18 W while maintaining the CPU 65°C above ambient temperature.
Forced Convection in a Porous Channel With Discrete Heat Sources
Authors: Cui C. , Huang X. Y. , Liu C. Y.
Published: July 2002

An experimental study was conducted on the heat transfer characteristics of flow through a porous channel with discrete heat sources on the upper wall. The temperatures along the heated channel wall were measured with different heat fluxes and the local Nusselt numbers were calculated at the different Reynolds numbers. The temperature distribution of the fluid inside the channel was also measured at several points. The experimental results were compared with that predicted by an analytical model using the Green’s integral over the discrete sources, and a good agreement between the two was obtained. The experimental results confirmed that the heat transfer would be more significant at leading edges of the strip heaters and at higher Reynolds numbers.
Tribology of Graphite and Concrete, Studied by Contact Electrical Resistance Measurement During Cyclic Compression
Authors: Luo Xiangcheng , Chung D. D. L.
Published: July 2002

The tribology of graphite and cement mortar was studied by contact electrical resistance measurement during cyclic compression. Elastic deformation and plastic deformation at asperities were distinctly observed through the reversible and irreversible decreases, respectively, of the contact resistance upon loading. Elastic deformation was dominant at the maximum stress. Plastic deformation progressed and then saturated upon stress cycling.
Rheological Behavior of Confined Fluids in Thin Lubricated Contacts
Authors: Tichy J.
Published: July 2002

Continuum based methods are traditionally thought to be of little value in describing boundary lubrication, or the mode of lubrication in molecular scale films that may occur at asperity interactions during the sliding of nominally flat surfaces. There is considerable experimental evidence, which suggests that the classical theory may be valid with modification to films as thin as several nanometers. In addition, lubricants, which exhibit viscous liquid properties in bulk, may form attached solid-like elastic layers when confined between solid surfaces. In the present paper, the simple “elastic foundation” concept is used to model the elastic layers, in contact with a viscous fluid film. Several typical bearing contact flow problems are solved, giving hope that boundary lubrication may eventually be modeled in the same manner as hydrodynamic lubrication in thicker films.
Multicriteria Optimization in Product Platform Design
Authors: Nelson Sigurd A. , Parkinson Matthew B. , Papalambros Panos Y.
Published: July 2002

A product platform is a set of common components, modules or parts from which a stream of derivative products can be created. Product platform design requires selection of the shared parts and assessment of the potential sacrifices in individual product performance that result from parts sharing. A multicriteria optimization problem can be formulated to study such decisions in a quantitative manner at the product performance level. Studying the Pareto sets that correspond to various derivative products leads to a systematic methodology for design decision making. Design of a nail gun platform is used to illustrate the concepts presented.
Development of a Grating Interferometer with Application to HDD Servo-Track Writing
Authors: Garner Harry D. , Lee Kok-Meng , Guo Lin
Published: July 2002

The development of a grating interferometer with application to the angular measurement of a hard disk drive actuator arm for application to the servo-track writing process is presented. First, the theoretical background related to the linear type grating interferometer is presented, and this theory is extended to the measurement of the angular displacement of a hard disk drive actuator arm using a linear grating. A vector based diffraction technique has also been developed as a tool for visualization and analysis of the grating interferometer design. Finally, experimental setups and results from a prototype grating interferometer design are presented and discussed to demonstrate the feasibility of the grating interferometer measurement system.
Design, Fabrication, and Testing of Ceramic Joints for High Temperature SiC/SiC Composites
Authors: Singh M. , Lara-Curzio E.
Published: July 2002

Various issues associated with the design and mechanical evaluation of joints of ceramic matrix composites are discussed. The specific case of an affordable, robust ceramic joining technology (ARCJoinT) to join silicon carbide (CG-Nicalon™) fiber-reinforced-chemically vapor infiltrated (CVI) silicon carbide matrix composites is addressed. Experimental results are presented for the time and temperature dependence of the shear strength of these joints in air up to 1200°C. From compression testing of double-notched joint specimens with a notch separation of 4 mm, it was found that the apparent shear strength of the joints decreased from 92 MPa at room temperature to 71 MPa at 1200°C. From shear stress-rupture testing in air at 1200°C it was found that the shear strength of the joints decreased rapidly with time from an initial shear strength of 71 MPa to a value of 17.5 MPa after 14.3 h. The implications of these results in relation to the expected long-term service life of these joints in applications at elevated temperatures are discussed.
Searching for Robust Minimal-Order Compensators
Authors: Wang Qian , Stengel Robert F.
Published: July 2002

A method of designing a family of robust compensators for a single-input/single-output linear system is presented. Each compensator’s transfer function is found by using a genetic-algorithm search for numerator and denominator coefficients. The search minimizes the probabilities of unsatisfactory stability and performance subject to real parameter variations of the plant. As the search progresses, probabilities are estimated by Monte Carlo evaluation. The design procedure employs a sweep from the lowest feasible transfer-function order to higher order, terminating either when design goals have been achieved or when no further improvement in robustness is evident. The method provides a means for estimating the best possible compensation of a given order based on repeated searches.
A New QFT Design Methodology for Feedback Systems Under Input Saturation
Authors: Wu Wei , Jayasuriya Suhada
Published: July 2002

Presented in this paper is a design methodology for robust stability and robust performance for a large class of plants subject to an input saturation nonlinearity. Based on Horowitz’s 3-DOF linear design method, a more general form for the additional loop transmission around the saturating element is proposed to design the third degree of freedom Hs, for Type n plants, n⩾1. Robust stability is established with the circle criterion and the describing function technique, and robust performance is improved by imposing nonovershooting conditions. All stability and performance requirements are then transferred into frequency domain design bounds which are easily obtained using QFT design techniques. This procedure applies to all SISO, Type n, stable plants with uncertainties (parametric or nonparametric), and to marginally stable and conditionally stable plants as well.
Adaptive Neurocontrol of Heat Exchangers
Authors: Dı´az Gerardo , Sen Mihir , Yang K. T. , McClain Rodney L.
Published: July 2002

This paper investigates the use of adaptive artificial neural networks (ANNs) to control the exit air temperature of a compact heat exchanger. The controllers, based on an internal model control scheme, can be adapted on-line on the basis of different performance criteria. By numerical simulation a methodology by which the weights and biases of the neural network are modified according to these criteria was developed. An ANN controller for an air-water compact heat exchanger in an experimental facility is then implemented. The parameters of the neural net are modified using three criteria: minimization of target error, stabilization of the closed-loop performance of the controller, and minimization of a performance index that we have taken to be the energy consumption. It is shown that the neural network is able to control the air exit temperature in the heat exchanger. The neurocontroller is able to adapt to major structural changes in the system as well as to simultaneously minimize the amount of energy used.
Tracking of High Acceleration Movements With a Pneumatic Impedance Controller
Authors: Guihard M. , Gorce P.
Published: July 2002

An original structure to simulate the vertical dynamic jump of one leg is proposed in this paper. The aim is to reproduce a motion composed of an upward propulsion, a flying and a landing phase. The leg is modeled as a three rigid body moved by three pneumatic actuators. A dynamic model of the structure is first presented and the design of the impedance controller is developed based on the nonlinear control theory. The originality of the controller lays in the consideration of impedance behavior at each joint during free and constrained phases. The asymptotic stability is ensured using Popov criteria. The simulations proposed are based on physiological data coming from experiments of a human performing a jump. This specific motion will show the performances of the controller especially during the propulsion and the landing phases because of their high acceleration characteristics.
A Dynamic Analysis of the Oscillations in a Chain Drive
Authors: Troedsson I. , Vedmar L.
Published: July 2002

A model is presented in which the oscillations, and the forces thus produced, in a chain drive, working at moderate and high speed, can be calculated. Since the outer system affects the result it has been necessary to include this in the model. The mass of the chain is included in the model and both the gravitational forces and the inertia forces in the chain are taken into account. The elasticity in the links is included. The sprockets are connected by two spans, both of which have to be included in the model to fulfill the equilibrium equations for the rollers in contact with the sprockets. The position of the chain is given by the geometric conditions as well as the equilibrium condition. On the slack side a chain tensioner is used to reduce the transverse oscillation, which occur at higher speeds.
A Classification of Spatial Stiffness Based on the Degree of Translational–Rotational Coupling
Authors: Huang Shuguang , Schimmels Joseph M.
Published: July 2002

Previously, we have shown that, to realize an arbitrary spatial stiffness matrix, spring components that couple the translational and rotational behavior along/about an axis are required. We showed that, three such coupled components and three uncoupled components are sufficient to realize any full-rank spatial stiffness matrix and that, for some spatial stiffness matrices, three coupled components are necessary. In this paper, we show how to identify the minimum number of components that provide the translational-rotational coupling required to realize an arbitrarily specified spatial stiffness matrix. We establish a classification of spatial stiffness matrices based on this number which we refer to as the “degree of translational–rotational coupling” (DTRC). We show that the DTRC of a stiffness matrix is uniquely determined by the spatial stiffness mapping and is obtained by evaluating the eigenstiffnesses of the spatial stiffness matrix. The topological properties of each class are identified. In addition, the relationships between the DTRC and other properties identified in previous investigations of spatial stiffness behavior are discussed.
Numerical–Experimental Method for the Validation of a Controlled Stiffness Femoral Prosthesis
Authors: Simo˜es J. A. , Monteiro J. , Vaz M. A.
Published: July 2002

The aim of this paper is to describe a new numerical–experimental method to determine the stiffness of a conceptual proximal femoral prototype. The methodology consists of the comparison of the numerical and experimental displacement distributions of the prosthesis loaded as a cantilever beam to validate a design concept: controlled stiffness prosthesis. The manufactured prototype used to test the applicability of the numerical–experimental procedure integrates a stiff metal core bonded to a composite material made of an epoxy resin reinforced with carbon-glass braided pre-forms. The prosthesis with an embedded controlled stiffness concept was obtained by varying the geometry of the core with the composite layer thickness.
Active Control of Translating Media With Arbitrarily Varying Length
Authors: Zhu W. D. , Ni J. , Huang J.
Published: July 2002

The general control laws for pointwise controllers to dissipate vibratory energies of translating beams and strings with arbitrarily varying length are presented. Special domain and boundary control laws that can be easily implemented result as a special case. Sufficient conditions for uniform stability and uniform exponential stability of controlled systems are established via Lyapunov stability criteria. Numerical simulations demonstrate the effectiveness of the active controllers in stabilizing translating media during both extension and retraction. Optimal gains leading to the fastest rates of decay of vibratory energies of controlled systems are identified. It is shown that under the optimal control gains, translating media can be completely stabilized during extension and retraction.
Development of a Flexible Laser Ultrasonic Probe
Authors: Hopko Sandra N. , Ume I. Charles , Erdahl Dathan S.
Published: July 2002

Ultrasonics is a widely used nondestructive testing technique, which is often applied off-line for weld quality inspection. Laser ultrasonic (LU) inspection systems have the potential for on-line application, providing the means to identify unacceptable welds as they are formed. Because LU systems are non-contacting, they can be used for testing moving specimens or for operation in hazardous and/or high temperature environments. A highly versatile system can be created when an optical fiber delivery system is incorporated into the design. Introduction of a focusing objective increases the allowable working distance and permits stronger generation using material ablation as the generating mechanism. This paper describes the development of a laser ultrasonic probe using an optical fiber delivery system with a distal end, focusing objective. The optical fiber delivery system can be configured as a single fiber source, a linear array (fiber bundle) or a phased array. Results include experimentally obtained directivity patterns demonstrating ultrasonic generation using ablation sources. Thermoelastic source results are also included. This paper demonstrates the potential of the fiber tool and presents an overview of the weld control scheme.
Deformation of Inhomogeneous Elastic Solids With Two-Dimensional Damage
Authors: Luo J. J. , Daniel I. M.
Published: July 2002

A general correlation is derived between macroscopic stresses/strains and microscopic deformation on the damage surfaces for inhomogeneous elastic solids with two-dimensional damage. Assuming linear elastic behavior for the undamaged materials, the macroscopic deformation associated with nonlinear strains, or damage strains, is shown to be the weighted sum of the microscopic deformations on the damage surfaces. For inhomogeneous materials with periodic structures (laminated composites, for example) and various identifiable damage modes, simple relations are derived between the macroscopic deformation and microscopic damage. When the number of identifiable damage modes is less than or equal to the number of relevant measurable macroscopic strains, the correlation can be used to evaluate the damage progression from simple macroscopic stress and strain measurements. The simple case of a unidirectional fiber-reinforced composite under longitudinal load is used to show how the results can help detect and characterize the damage using macroscopic measurements, without resorting to assumptions of detailed microscopic deformation mechanisms.
Experimental Determination of KI for Short Internal Cracks
Authors: Bearden K. , Dally J. W. , Sanford R. J.
Published: July 2002

Since the pioneering discussion by Irwin, a significant effort has been devoted to determining stress intensity factors (K) using experimental methods. Techniques have been developed to determine stress intensity factors from photoelastic, strain gage, caustics, and moire´ data. All of these methods apply to a relatively long single-ended-edge crack. To date, the determination of K for internal cracks that are double-ended by experimental methods has not been addressed. This paper describes a photoelastic study of tension panels with both central and eccentric internal cracks. The data recorded in the experiments was analyzed using a new series solution for the opening-mode stress intensity factor for an internal crack. The data was also analyzed using the edge-crack series solution, which is currently employed in experimental studies. Results indicated that the experimental methods usually provided results accurate to within three to five percent if the series solution for the internal crack was employed in an overdeterministic numerical analysis of the data. Comparison of experimental results using the new series for the internal crack and the series for an edge crack showed the superiority of the new series.
Optimal Feedback Control of Vortex Shedding Using Proper Orthogonal Decomposition Models
Authors: Singh Sahjendra N. , Myatt James H. , Addington Gregory A. , Banda Siva , Hall James K.
Published: July 2002

This paper treats the question of control of two-dimensional incompressible, unsteady wake flow behind a circular cylinder at Reynolds number Re=100. Two finite-dimensional lower order models based on proper orthogonal decomposition (POD) are considered for the control system design. Control action is achieved via cylinder rotation. Linear optimal control theory is used for obtaining stabilizing feedback control systems. An expression for the region of stability of the system is derived. Simulation results for 18-mode POD models obtained using the control function and penalty methods are presented. These results show that in the closed-loop system mode amplitudes asymptotically converge to the chosen equilibrium state for each flow model for large perturbations in the initial states.
Combining a Multirate Repetitive Learning Controller With Command Shaping for Improved Flexible Manipulator Control
Authors: Rhim Sungsoo , Hu Ai-Ping , Sadegh Nader , Book Wayne J.
Published: July 2002

Comand shaping, a feedforward approach used to control flexible manipulators, performs most effectively when applied to a linear system. In practice, various nonlinearities are present in a given system that will deteriorate the performance of command shaping. In this work, a multirate repetitive learning controller (MRLC) is used in conjunction with a command shaping method known as the optimal arbitrary time-delay filter (OATF) for discrete-time joint control of a single flexible link manipulator containing nonlinearities. With very little a priori knowledge of the given system, a MRLC is able to cancel the repetitive tracking errors caused by nonlinearities at select frequencies and thereby achieve near-perfect tracking of a periodic reference trajectory. By doing this, a MRLC controls the joint of the flexible link manipulator to follow a given shaped command more closely, thus allowing the OATF to more effectively attenuate residual manipulator tip vibrations. It is shown both analytically and experimentally that this combined control strategy is more effective than a conventional PID and OATF controller at attenuating residual tip vibrations.
Mode II Edge Delamination of Compressed Thin Films
Authors: Balint D. S. , Hutchinson J. W.
Published: July 2002

Ceramic coatings deposited on metal substrates generally develop significant compressive stresses when cooled from the temperature at which they are processed as a result of thermal expansion mismatch. One of the main failure modes for these coatings is edge delamination. For an ideally brittle interface, the edge delamination of a compressed thin film involves mode II interface cracking. The crack faces are in contact with normal stress acting across the faces behind the advancing tip. Frictional shielding of the crack tip has been shown to increase the apparent fracture toughness. Roughness effects associated with the separating faces can also contribute to the apparent toughness. A model of mode II steady-state edge delamination that incorporates combined friction and roughness effects between the delaminated film and substrate is proposed and analyzed. This model is used to assess whether frictional shielding and surface roughness effects are sufficient to explain the large apparent mode II fracture toughness values observed in experiments.
Using Computer Simulation to Validate and Optimize the Design of an Innovative Electronic Packaging Concept
Authors: Beyerlein Dagmar , Hornberger Lee E.
Published: July 2002

Reducing integrated circuit (IC) plastic packaging production costs by improving the transfer mold and leadframe designs is a costly and time-consuming process. Rather than building mold and leadframe prototypes to perform empirical studies, this research describes how C-MOLD, a microchip encapsulation simulation software application, was used to validate and optimize an innovative mold and leadframe design that has the potential to reduce raw material waste associated with packaging by more than 59 percent. Estimates indicate that the proposed design will cut annual production costs by more than $600,000.
The Surface-Tension-Driven Flow of Blood From a Droplet Into a Capillary Tube
Authors: Huang Wei , Bhullar Raghbir S. , Fung Yuan Cheng
Published: July 2002

In tissue, medical, or dental engineering, when blood comes into contact with a new artificial material, the flow may be influenced by surface tension between the blood and the surface of the material. The effect of surface tension on the flow of blood is significant, especially in microscale. The leading edge of the flowing blood is the triple point where the blood, the material surface, and a stationary gas or fluid meet. The movement of the triple point, i.e., the advancing front of the flow, is driven by surface tension, resisted by viscous shear stress, and balanced by the inertial force (−mass×acceleration). In this article, the dynamics is illustrated in detail in the case of blood flowing into a capillary tube by contact. The capillary tube draws the blood into it. It is shown theoretically that initially the flow of blood in the capillary has a large acceleration, followed by a relatively large deceleration over the next short period of time, then the acceleration becomes small and oscillatory. The velocity history appears impulsive at first, then slows down. The history of the length of blood column appears smooth after integration. Existing solutions of the Navier–Stokes equation permit the analysis of simpler cases. Further fluid mechanics development is needed to meet the practical needs of bioengineering. The importance of experimental study of surface tension and contact angle over a biological surface or a man-made material as a future direction of research is pointed out.
Predictions of NOx Formation Under Combined Droplet and Partially Premixed Reaction of Diffusion Flame Combustors
Authors: Rizk N. K. , Chin J. S. , Marshall A. W. , Razdan M. K.
Published: July 2002

A methodology is presented in this paper on the modeling of NOx formation in diffusion flame combustors where both droplet burning and partially premixed reaction proceed simultaneously. The model simulates various combustion zones with an arrangement of reactors that are coupled with a detailed chemical reaction scheme. In this model, the primary zone of the combustor comprises a reactor representing contribution from droplet burning under stoichiometric conditions and a mixing reactor that provides additional air or fuel to the primary zone. The additional flow allows forming a fuel vapor/air mixture distribution that reflects the unmixedness nature of the fuel injection process. Expressions to estimate the extent of deviation in fuel/air ratios from the mean value, and the duration of droplet burning under stoichiometric conditions were derived. The derivation of the expressions utilized a data base obtained in a parametric study performed using a conventional gas turbine combustor where the primary zone equivalence ratio varied over a wide range of operation. The application of the developed model to a production combustor indicated that most of the NOx produced under the engine takeoff mode occurred in the primary as well as the intermediate regions. The delay in NOx formation is attributed to the operation of the primary zone under fuel rich conditions resulting in a less favorable condition for NOx formation. The residence time for droplet burning increased with a decrease in engine power. The lower primary zone gas temperature that limits the spray evaporation process coupled with the leaner primary zone mixtures under idle and low power modes increases the NOx contribution from liquid droplet combustion in diffusion flames. Good agreement was achieved between the measured and calculated NOx emissions for the production combustor. This indicates that the simulation of the diffusion flame by a combined droplet burning and fuel vapor/air mixture distribution offers a promising approach for estimating NOx emissions in combustors, in particular for those with significant deviation from traditional stoichiometry in the primary combustion zone.
Thermal Management of Outdoor Electronic Cabinets Using Soil Heat Exchangers
Authors: Hegab Hisham E. , Zimmerman Eric B. , Colwell Gene T.
Published: July 2002

Telephone companies utilize densely packed electronics in outdoor metal cabinets for routing calls between customers. As a result of the increasing power densities of electronics, companies are looking for innovative methods of providing system level cooling such as using soil heat exchangers. Numerical simulation using a system of lumped thermal capacitances coupled to a soil finite element model is used to predict the transient thermal behavior of a cabinet. The cabinet model has been verified in previous studies by comparison with experimental measurements on a commercial telecommunications cabinet and is shown to predict temperature trends well. The effects of transient heat load, soil properties, and heat exchanger geometry are examined. Results reveal soil heat exchangers have the capability to provide the necessary cooling for relatively low power outdoor cabinets. However, the temperature of the soil surrounding the heat exchanger may increase daily if the number and spacing of pipes is not adequate to handle the desired heat dissipation load.
The Application of Pressure- and Temperature-Sensitive Paints to an Advanced Compressor
Authors: Navarra Kelly R. , Rabe Douglas C. , Fonov Sergey D. , Goss Larry P. , Hah Chunill
Published: July 2002

An innovative pressure-measurement technique that employs the tools of molecular spectroscopy has been widely investigated by the aerospace community. Measurements are made via oxygen-sensitive molecules attached to the surface of interest as a coating, or paint. The pressure-sensitive-paint (PSP) technique is now commonly used in stationary wind-tunnel tests; this paper presents the use of this technique in advanced turbomachinery applications. New pressure- and temperature-sensitive paints (P/TSPs) have been developed for application to a state-of-the-art transonic compressor where pressures up to 1.4 atm and surface temperatures to 90°C are expected for the suction surface of the first-stage rotor. PSP and TSP data images have been acquired from the suction surface of the first-stage rotor at 85 percent of the corrected design speed for the compressor near-stall condition. A comparison of experimental results with CFD calculations is discussed.
Time-Accurate, 3-D Computation of Wire Sweep During Plastic Encapsulation of Electronic Components
Authors: Yang H.-Q. , Bayyuk S. , Mazumder S. , Lowry S. , Krishnan A. , Przekwas A. , Nguyen L.
Published: July 2002

A computational technique is developed for accurate prediction of wire sweep during encapsulation of electronic components by transfer molding. The technique advances the current state-of-the-art by modeling the effects of the two-phase flow involved, the effects of the polymerization of the melt, and the effects of the time-dependence of the fluid and heat flows and of the wire stresses and deformations. The computational techniques used for separately computing the fluid and heat flows, for separately computing the structural-dynamic stresses and deformations, and for establishing two-way coupling between the separately computed “flow” and “structural” solutions are described. Validations comparing the computational predictions with the corresponding analytical solutions for reference cases with straight wires immersed in flowing liquids are presented and discussed. The validation results show close agreement with theory, and demonstrate the need for using large-deformation theory for computing wire deformations and stresses. Demonstrative results for the unsteady flowfield and wire sweep in a TO-220 package are also presented and discussed.
Modified General Equation for the Design of Capillary Tubes
Authors: Zhang C. L. , Ding G. L.
Published: July 2002

In order to improve the design efficiency of capillary tubes, capillary tube models have been developed. Yilmaz and U¨nal presented a general approximate analytic equation for the design of adiabatic capillary tubes. In this work, the Yilmaz-U¨nal equation was analyzed in detail and some problems were found. Consequently, a modified general equation was developed and verified by theoretical and experimental data.
Comparative Analysis of Regression and Artificial Neural Network Models for Wind Turbine Power Curve Estimation
Authors: Li Shuhui , Wunsch Donald C. , O’Hair Edgar , Giesselmann Michael G.
Published: July 2002

This paper examines and compares regression and artificial neural network models used for the estimation of wind turbine power curves. First, characteristics of wind turbine power generation are investigated. Then, models for turbine power curve estimation using both regression and neural network methods are presented and compared. The parameter estimates for the regression model and training of the neural network are completed with the wind farm data, and the performances of the two models are studied. The regression model is shown to be function dependent, and the neural network model obtains its power curve estimation through learning. The neural network model is found to possess better performance than the regression model for turbine power curve estimation under complicated influence factors.
Fabrication of Non-Assembly Mechanisms and Robotic Systems Using Rapid Prototyping
Authors: Mavroidis Constantinos , DeLaurentis Kathryn J. , Won Jey , Alam Munshi
Published: July 2002

In this paper, the application of Rapid Prototyping in fabricating non-assembly robotic systems and mechanisms is presented. Using two Rapid Prototyping techniques, Stereolithography and Selective Laser Sintering, prototypes of mechanical mobile joints were fabricated. The designs of these component joints were then used to fabricate the articulated structure of experimental prototypes for two robotic systems: (1) a three-legged parallel manipulator, (2) a four degree-of-freedom finger of a five-fingered robotic hand. These complex multi-articulated, multi-link, multi-loop systems have been fabricated in one step, without requiring assembly while maintaining their desired mobility. The feasibility and usefulness of Rapid Prototyping as a method for the fabrication of these non-assembly type mechanisms and robotic systems is the focus of this work.
The Impact of Sliding Blades in a Rotary Compressor
Authors: Huang Yuan Mao , Liaw Yung-Shane
Published: July 2002

The purpose of this study was to analyze the impact of blades with slots in a rotary compressor. The equations for contact forces were derived from Newton’s law. Updated moving Lagrangian descriptions with the hybrid technique and the Newark time integration method were used to determine the nodal displacement vectors. The finite element method was used to analyze the contact forces and the stresses of blades. The maximum blade contact force of 2.3 KN was larger than the maximum static force of 1 KN. The maximum blade impact Von Mises stress of 12.3 Mpa that occurred at the contact point was greater than the previous calculated static stress of 5.15 Mpa. Hence, the impact effect was significant. Experimental modal analysis was also used to determine the first and second natural frequencies of blades.
A PC-Based Synchronous Controller for NC Gear Grinding Machines Using Multithread CBN Wheel
Authors: Emura T. , Wang L. , Yamanaka M. , Nakamura H. , Kato Y. , Teshigawara Y.
Published: July 2002

This paper describes a synchronous controller for high-productivity NC gear grinding machines that use a screw-shaped CBN wheel of multithread. The authors developed a high-precision controller for productive-type NC gear grinding machines in 1995. Because it was based on analog circuits, it required very complex electrical circuits. In this paper, we propose a PC-based synchronous controller to decrease production costs and add useful functions to it. The most useful one added this time is a function to increase pitch accuracy of gear ground with the multithread CBN wheel. Next useful one is a function to attain high-accuracy initial meshing between gear and CBN wheel. Because grinding-spindle and work spindle rotate at a high-speed, two-phase type PLL is applied to the controller. Grinding experiments showed that the newly developed controller has excellent performance.
Reconciliation of Rotordynamic Models With Experimental Data
Authors: Maslen E. H. , Vázquez J. A. , Sortore C. K.
Published: July 2002

A computationally efficient strategy is presented for adjusting analytic rotordynamic models to make them consistent with experimental data. The approach permits use of conventional rotordynamic models derived using finite element methods in conjunction with conventional plant identification models derived from impact or sine sweep testing in a transfer function or influence coefficient format. The underlying assumption is that the predominant uncertainties in engineered models occur at discrete points as effects like shrink fits, seal coefficients or foundation interactions. Further, it is assumed that these unmodeled or poorly modeled effects are essentially linear (at least within the testing and expected operating domains). Matching is accomplished by deriving a dynamic model for these uncertain effects such that the resulting composite model has a transfer function which matches that obtained experimentally. The derived augmentations are computationally compatible with the original rotor model and valid for stability or forced response predictions. Further, computation of this augmentation is accomplished using well developed and widely disseminated tools for modern control. Background theory and a complete recipe for the solution are supported by a number of examples.