bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Frequencies of Rotating Uniform Beams with Coriolis Effects
Authors: Hashemi S. M. , Richard M. J.
Published: July 2002

A Dynamic Finite Element (DFE) for vibrational analysis of rotating assemblages composed of beams is presented in which the complexity of the acceleration, due to the presence of gyroscopic, or Coriolis forces, is taken into consideration. The dynamic trigonometric shape functions of uncoupled bending and axial vibrations of an axially loaded uniform beam element are derived in an exact sense. Then, exploiting the Principle of Virtual Work together with the nodal approximations of variables, based on these dynamic shape functions, leads to a single frequency dependent stiffness matrix which is Hermitian and represents both mass and stiffness properties. A Wittrick-Williams algorithm, based on a Sturm sequence root counting technique, is then used as the solution method. The application of the theory is demonstrated by two illustrative examples of vertical and radial beams where the influence of Coriolis forces on natural frequencies of the clamped-free rotating beams is demonstrated by numerical results.
Hydrodynamic Focusing for a Micromachined Flow Cytometer
Authors: Lee Gwo-Bin , Hung Chen-I , Ke Bin-Jo , Huang Guan-Ruey , Hwei Bao-Herng , Lai Hui-Fang
Published: July 2002

This paper describes hydrodynamic focusing inside a micromachined flow cytometer. Flow cytometry is a process whereby cells are analyzed and sorted based on hydrodynamic focusing phenomenon and specific cellular characteristics. In this study, the hydrodynamic focusing phenomenon is first modeled by employing potential flow theory. Then the flow field inside the flow cytometer is numerically simulated. The effect of the device geometry and relative sheath and sample flow rate on the focusing of the center flow is explored systematically. At last, a micromachine-based flow chamber is designed and fabricated on plastic substrates as a micro flow cytometer. Hydrodynamic focusing is verified with the use of microscopic visualization of water sheath flows and dye-containing sample flow. Experimental data indicate that the size of focused sample stream can be reduced to about 3 μm, which is applicable to cell sorting and counting.
Design of a Nonlinear Adaptive Controller for an Electrohydraulic Actuator1
Authors: Ziaei K. , Sepehri N.
Published: July 2002

This paper presents a new implementation of indirect model reference adaptive (MRA) control scheme for positioning of hydraulic actuators that operate by low-cost proportional valves. A proper linear discrete-time plant model is used which has dead-time and no zeros, eliminating the possibility of unstable pole-zero cancellation. The robustness of the parameter adaptation is achieved by employing the recursive least-squares algorithm in combination with a dead-zone in the adaptive law. It is shown that while the controller is adequate for hydraulic valves with linear flow characteristics, it exhibits low performance in the presence of deadband and nonlinear orifice opening characteristics of low-cost proportional valves. The linear plant model is therefore augmented by adding a static nonlinearity. The resulting nonlinear MRA controller is shown to have improved performance over its linear counterpart. Step-by-step experiments are presented to confirm the effectiveness and performance improvement of the proposed method.
Robust Performance Repetitive Control Systems
Authors: Li Jianwu , Tsao Tsu-Chin
Published: July 2002

This paper addresses analysis and synthesis of robust stability and robust performance repetitive control systems. The repetitive control design problem is formulated as a standard feedback form in the linear fractional transformation form such that the standard numerical optimization software can be used to obtain the solution. The main idea of the robust repetitive control system design lies in introducing a fictitious complex uncertainty to replace the long delay chain in the internal model of the repetitive control system. This drastically reduces the order of the augmented plant for controller synthesis and hence generates a low order compensator, which in conjunction with the pure delay renders a repetitive controller that can be implemented efficiently in real time. The proposed approach can be applied to both the continuous and discrete-time domain repetitive control design for unstable open-loop plant. Sufficient conditions for the robust stability and robust performance repetitive control systems are presented. Conservatism analysis shows that the sufficient conditions become necessary when the pure delay approaches infinity. The robust repetitive control is applied to an electrohydraulic actuator for tracking periodic trajectories. Experimental results are presented to illustrate the design procedure and control system performance.
Moment Lyapunov Exponent and Stochastic Stability of Two Coupled Oscillators Driven by Real Noise
Authors: Sri Namachchivaya N. , Van Roessel H. J.
Published: July 2002

In a recent paper an asymptotic approximation for the moment Lyapunov exponent, gp, of two coupled oscillators driven by a small intensity real noise was obtained. The utility of that result is limited by the fact that it was obtained under the assumption that the moment p is small, a limitation which precludes, for example, the determination of the stability index. In this paper that limitation is removed and an asymptotic approximation valid for arbitrary p is obtained. The results are applied to study the moment stability of the stationary solutions of structural and mechanical systems subjected to stochastic excitation.
Numerical Study of Steady Forced Convection in a Grooved Annulus Using a Design of Experiments
Authors: Sommerer Yannick , Lauriat Guy
Published: July 2002

Numerical simulations have been performed to study the flow and heat transfer characteristics in the annular space between an inner smooth-cylinder rotating at constant angular velocity and an outer stationary grooved one. A first series of calculations were conducted to determine the ranges of Taylor number and longitudinal aspect ratio for which a two-dimensional modeling can be considered as valid. To this end, a map showing the domain of validity of two dimensional computations is presented. The assumption of circumferential periodicity of the flow is then justified in the range of Taylor numbers investigated. A number of simulations were carried out to investigate the effects of the geometrical parameters describing the cross section of the grooved annulus for various Taylor numbers. To end, correlations describing the influences on the main parameters both on the friction factor and Nusselt numbers are derived by using a design of experiments.
Convective Heat Transfer and Aerodynamics in Axial Flow Turbines
Authors: Dunn Michael G.
Published: July 2002

The primary focus of this paper is convective heat transfer in axial flow turbines. Research activity involving heat transfer generally separates into two related areas: predictions and measurements. The problems associated with predicting heat transfer are coupled with turbine aerodynamics because proper prediction of vane and blade surface-pressure distribution is essential for predicting the corresponding heat transfer distribution. The experimental community has advanced to the point where time-averaged and time-resolved three-dimensional heat transfer data for the vanes and blades are obtained routinely by those operating full-stage rotating turbines. However, there are relatively few CFD codes capable of generating three-dimensional predictions of the heat transfer distribution, and where these codes have been applied the results suggest that additional work is required. This paper outlines the progression of work done by the heat transfer community over the last several decades as both the measurements and the predictions have improved to current levels. To frame the problem properly, the paper reviews the influence of turbine aerodynamics on heat transfer predictions. This includes a discussion of time-resolved surface-pressure measurements with predictions and the data involved in forcing function measurements. The ability of existing two-dimensional and three-dimensional Navier–Stokes codes to predict the proper trends of the time-averaged and unsteady pressure field for full-stage rotating turbines is demonstrated. Most of the codes do a reasonably good job of predicting the surface-pressure data at vane and blade midspan, but not as well near the hub or the tip region for the blade. In addition, the ability of the codes to predict surface-pressure distribution is significantly better than the corresponding heat transfer distributions. Heat transfer codes are validated against measurements of one type or another. Sometimes the measurements are performed using full rotating rigs, and other times a much simpler geometry is used. In either case, it is important to review the measurement techniques currently used. Heat transfer predictions for engine turbines are very difficult because the boundary conditions are not well known. The conditions at the exit of the combustor are generally not well known and a section of this paper discusses that problem. The majority of the discussion is devoted to external heat transfer with and without cooling, turbulence effects, and internal cooling. As the design community increases the thrust-to-weight ratio and the turbine inlet temperature, there remain many turbine-related heat transfer issues. Included are film cooling modeling, definition of combustor exit conditions, understanding of blade tip distress, definition of hot streak migration, component fatigue, loss mechanisms in the low turbine, and many others. Several suggestions are given herein for research and development areas for which there is potentially high payoff to the industry with relatively small risk.
Microturbine/Fuel-Cell Coupling for High-Efficiency Electrical-Power Generation
Authors: Massardo A. F. , McDonald C. F. , Korakianitis T.
Published: July 2002

Microturbines and fuel cells are currently attracting a lot of attention to meet future users needs in the distributed generation market. This paper addresses a preliminary analysis of a representative state-of-the-art 50-kW microturbine coupled with a high-temperature solid-oxide fuel cell (SOFC). The technologies of the two elements of such a hybrid-power plant are in a different state of readiness. The microturbine is in an early stage of pre-production and the SOFC is still in the development phase. It is premature to propose an optimum solution. Based on today’s technology the hybrid plant, using natural gas fuel, would have a power output of about 389 kW, and an efficiency of 60 percent. If the waste heat is used the overall fuel utilization efficiency would be about 80 percent. Major features, parameters, and performance of the microturbine and the SOFC are discussed. The compatibility of the two systems is addressed, and the areas of technical concern, and mismatching issues are identified and discussed. Fully understanding these, and identifying solutions, is the key to the future establishing of an optimum overall system. This approach is viewed as being in concert with evolving technological changes. In the case of the microturbine changes will be fairly minor as they enter production on a large scale within the next year or so, but are likely to be significant for the SOFC in the next few years, as extensive efforts are expended to reduce unit cost. It is reasonable to project that a high performance and cost-effective hybrid plant, with high reliability, will be ready for commercial service in the middle of the first decade of the 21st century. While several microturbines can be packaged to give an increased level of power, this can perhaps be more effectively accomplished by coupling just a single gas turbine module with a SOFC. The resultant larger power output unit opens up new market possibilities in both the industrial nations and developing countries.
Life Prediction for Linear Rolling Element Bearings: A New Approach to Reliable Life Assessment
Authors: Shimizu Shigeo , Sharma Chandra S. , Shirai Takeki
Published: July 2002

A new approach to the life assessment for linear bearings using three-parameter Weibull distribution is discussed and theoretical basic dynamic load ratings are calculated for linear motion ball guides (LMBG) and ball bushes. Life test experiments are also carried out for these two types of linear bearings with varying design features for each type. The concept of a minimum life prior to which there is no failure, is introduced in the analysis of the life test data. The effects of introducing ball cages in LMBGs and rounding of the edges in the case of ball bushes on their lives, basic dynamic load ratings, and the λbm factors are examined. It is observed that compared with a two-parameter Weibull distribution, an analysis based on a three-parameter Weibull distribution clearly reveals the differences in the lives of linear bearings for changes in their designs.
Potentials for Site-Specific Design of MW Sized Wind Turbines
Authors: Thomsen K. , Fuglsang P. , Schepers G.
Published: July 2002

The potential for site specific design of MW sized wind turbines is quantified by comparing design loads for wind turbines installed at a range of different sites. The sites comprise on-shore normal flat terrain stand-alone conditions and wind farm conditions together with offshore and mountainous complex terrain wind farms. The design loads are established for a 1 MW active stall regulated wind turbine with the aeroelastic code HAWC. The load analysis is limited to fatigue loads. We do not consider ultimate loads in this paper. The results illustrate the differences in design wind conditions for different sites and the related differences in design loads for the 1 MW wind turbine. Based on the difference in the design loads, the potentials for site specific design of the wind turbine main components are identified. The results show that the variation in aerodynamically driven loads and energy production can be more than 50% between the different sites. It is concluded that site specific design is feasible for some of the main components. In particular, site specific changes are feasible for the tower, nacelle components, and for the blades in the flapwise direction. It is also evaluated whether the IEC61400-1 standard [see Ref. [4], International Electrochemical Commission (1999)] is representative for the different sites. A comparison with design loads based on the IEC61400-1 illustrates that the six different sites can be described by the standard design classes.
Biorthogonal Wavelet Based Identification of Fast Linear Time-Varying Systems—Part II: Algorithms and Performance Analysis12
Authors: Zhao Haipeng , Bentsman Joseph
Published: July 2002

The present work proposes a new class of algorithms for identification of fast linear time-varying systems on short time intervals, based on the biorthogonal function decomposition. When certain features of the system dynamics are known a priori, the algorithms admit their embedding into the identification procedure through the choice of the matching bases, yielding the rapidly convergent identification laws. The speed-up is attained via utilizing both time and frequency localized bases, permitting identification of fewer coefficients without noticeable loss of accuracy. Simulation shows that the resulting high speed identification algorithms can reject small persistent random disturbances as well as capture the fast changes in system dynamics. The algorithm development is based on the results of Part I where it is shown that the sets of all bounded-input-bounded-output (BIBO) stable or l2-stable linear discrete-time-varying (LTV) systems are Banach spaces, and modeling and identification of these systems are reducible to linear approximation problems in a Banach space setting.
Coupled deformation-diffusion effects in the mechanics of faulting
and failure of geomaterials
Authors: Rudnicki JW
Published: July 2002

This review article discusses the applications of poroelasticity to the mechanics of faulting and failure in geomaterials. Values of material parameters inferred from laboratory and field studies are summarized. Attention is focused on solutions for shear dislocations and shear cracks. A common feature is that undrained response, invoked by rapid slip or deformation, is stiffer than drained response, which occurs for slower slip or deformation. The time and spatial variation of the stress and pore pressure is different for slip on permeable and impermeable planes. These solutions are applied to interpretation of water well level changes due to slip, earthquake precursory processes, and stabilization of spreading slip zones. Inclusion models for reservoirs, aquifers, and other inhomogeneities are formulated and the results are applied to stress and strain changes caused by fluid mass injection or withdrawal.
Prediction and Diagnosis of Propagated Errors in Assembly Systems Using Virtual Factories
Authors: Baydar Cem M. , Saitou Kazuhiro
Published: July 2002

Large-scale automated assembly systems are widely used in automotive, aerospace and consumer electronics industries to obtain high quality products in less time. However, one disadvantage of these automated systems is that they are composed of too many working parameters. Since it is not possible to monitor all these parameters during the assembly process, an undetected error may propagate and result in a more critical detected error. In this paper, a unique way of detecting and diagnosing these types of failures by using Virtual Factories is discussed. A Virtual Factory was developed by building and linking several software modules to predict and diagnose propagated errors. A multi-station assembly system was modeled and a previously discussed “off-line prediction and recovery” method was applied. The obtained results showed that this method is capable of predicting propagated errors, which are too complex to solve for a human expert.
Design and Fabrication of an Active Gravity Balanced Planar Mechanism Using Auxiliary Parallelograms
Authors: Agrawal Sunil K. , Gardner Glenn , Pledgie Stephen
Published: July 2002

This paper describes the design of an active gravity balanced planar mechanism, where auxiliary parallelograms are used to physically locate the center of mass of the mechanism. A sliding carriage positions a counterweight directly above the center of mass of the mechanism in order to make the system gravity balanced. The sliding carriage uses joint encoder data from the mechanism to compute the location of the center of mass. Experiment results demonstrate the effectiveness of the approach.
The Effect of Space-Dependent Thermal Conductivity on the Steady Central Temperature of a Cylinder
Authors: Burmeister Louis C.
Published: July 2002

A transformation is presented that enables the center temperature of a cylinder to be expressed in terms of an integral of the peripheral temperature distribution for heat conduction with space-dependent thermal conductivity. Its predictions agree with exact answers and with numerical solutions obtained with finite difference methods for four test cases. The new result can be applied to a two-dimensional floating random-walk Monte Carlo procedure which previously was restricted to the case of constant thermal conductivity.
Recruitment of Tendon Crimp With Applied Tensile Strain
Authors: Hansen Kristi A. , Weiss Jeffrey A. , Barton Jennifer K.
Published: July 2002

The tensile stress-strain behavior of ligaments and tendons begins with a toe region that is believed to result from the straightening of crimped collagen fibrils. The in situ mechanical function is mostly confined to this toe region and changes in crimp morphology are believed to be associated with pathological conditions. A relatively new imaging technique, optical coherence tomography (OCT), provides a comparatively inexpensive method for nondestructive investigation of tissue ultrastructure with resolution on the order of 15 μm and the potential for use in a clinical setting. The objectives of this work were to assess the utility of OCT for visualizing crimp period, and to use OCT to determine how crimp period changed as a function of applied tensile strain in rat tail tendon fascicles. Fascicles from rat tail tendons were subjected to 0.5 percent strain increments up to 5 percent and imaged at each increment using OCT. A comparison between OCT images and optical microscopy images taken between crossed polarizing lenses showed a visual correspondence between features indicative of crimp pattern. Crimp pattern always disappeared completely before 3 percent axial strain was reached. Average crimp period increased as strain increased, but both elongation and shortening occurred within single crimp periods during the application of increasing strain to the fascicle.
The Mechanical Advantage of Local Longitudinal Shortening on Peristaltic Transport
Authors: Pal Anupam , Brasseur James G.
Published: July 2002

Whereas bolus transport along the esophagus results from peristaltic contractions of the circular muscle layer, it has been suggested that local shortening of the longitudinal muscle layer concentrates circular muscle fibers in the region where the highest contractile pressures are required. Here we analyze the mechanical consequences of local longitudinal shortening (LLS) through a mathematical model based on lubrication theory. We find that local pressure and shear stress in the contraction zone are greatly reduced by the existence of LLS. In consequence, peak contractile pressure is reduced by nearly 2/3 at physiological LLS, and this reduction is greatest when peak in LLS is well aligned with peak contractile pressure. We conclude that a peristaltic wave of local longitudinal muscle contraction coordinated with the circular muscle contraction wave has both a great physiological advantage (concentrating circular muscle fibers), and a great mechanical advantage (reducing the level of contractile force required to transport the bolus), which combine to greatly reduce circular muscle tone during esophageal peristalsis.
Solid Model Databases: Techniques and Empirical Results
Authors: McWherter David , Peabody Mitchell , Regli William C. , Shokoufandeh Ali
Published: July 2002

This paper presents techniques for managing solid models in relational database management systems. Our goal is to enable support for traditional database operations (sorting, distance metrics, range queries, nearest neighbors, etc) on large databases of solid models. We introduce an approach to compare models based on shape using information extracted from the model boundary representation into Model Signature Graphs. We show how the Model Signature Graphs can be used to compute topological distances among models and how to use these measures to create metric spaces for indexing and clustering of solid models. We believe this work will begin to bridge the solid modeling and database communities, enabling new paradigms for interrogation of CAD datasets based on the engineering content of solid models.
Feedback Stabilization of a Class of Unstable Nonholonomic Systems
Authors: Goodwine Bill , Zˇefran Milosˇ
Published: July 2002

This paper considers the design of nonlinear stabilizing controllers for a class of systems which exhibit unstable rolling dynamics or shimmy. Such systems can be used, for example, to approximate the complex dynamics of an aircraft landing gear structure. The controllers are designed using the well-known nonlinear control technique known as feedback linearization and some recent results pertaining to stability of hybrid systems. We consider three models of a system exhibiting shimmy, each progressively more sophisticated than the other and in each case we derive the controllers that stabilize the system. An interesting conclusion of this study is that the models that are more complex can be stabilized with simpler controllers.
Partial Entity Structure: A Compact Boundary Representation for Non-Manifold Geometric Modeling
Authors: Lee Sang Hun , Lee Kunwoo
Published: July 2002

Non-manifold boundary representations have become very popular in recent years and various representation schemes have been proposed, as they represent a wider range of objects, for various applications, than conventional manifold representations. As these schemes mainly focus on describing sufficient adjacency relationships of topological entities, the models represented in these schemes occupy storage space redundantly, although they are very efficient in answering queries on topological adjacency relationships. To solve this problem, in this paper, we propose a compact as well as fast non-manifold boundary representation, called the partial entity structure. This representation reduces the storage size to half that of the radial edge structure, which is one of the most popular and efficient of existing data structures, while allowing full topological adjacency relationships to be derived without loss of efficiency. In order to verify the time and storage efficiency of the partial entity structure, the time complexity of basic query procedures and the storage requirement for typical geometric models are derived and compared with those of existing schemes.
Robust Adaptive Compensation for a Class of Nonlinear Systems
Authors: Du Hongliu , Nair Satish S.
Published: July 2002

A robust adaptive design method is proposed for the on-line compensation of uncertainties, for a class of nonlinear systems. As an extension of previous work, the adaptive part of the control law uses a constructive Gaussian network without any prior training, and the control law provides robustness using a systematically designed sliding mode term. In the design, learning and control bounds are guaranteed by properly constructing the control architecture using the proposed methods. The robust adaptive control strategy, with the proposed design guidelines, has been validated using a hardware example case of a nonlinear robotic linkage system. Experiments have shown that the inclusion of the proposed stable learning and robust terms into the control design, using the proposed constructive methods, results in improved system performance for the example case system.
Effect of Microscale Mass Transport and Phase Change on Numerical Prediction of Freezing in Biological Tissues
Authors: Devireddy Ramachandra V. , Smith David J. , Bischof John C.
Published: July 2002

A numerical model incorporating the microscale heat and mass transport in biological tissue during freezing is developed. The heat transfer problem is formulated in a general one-dimensional coordinate system (cartesian, cylindrical or spherical), and a finite control volume discretization is used. The latent heat release for each control volume in the domain is determined by the cellular water transport and intracellular ice formation processes occurring there (a coupled thermal/biophysical approach). The coupled model is applied to two cryobiological freezing problems, with different geometry and boundary conditions. The temperature dependent thermal properties of water and the biophysical properties of two biological tissues, normal rat liver and Dunning AT-1 rat prostate tumor tissue are used to simulate both the micro and macroscale freezing processes. A major advantage of the coupled thermal/biophysical model is its unique ability to predict both the macroscale thermal response and the microscale biophysical response at various locations within the tissue domain during a freezing process, simultaneously. Thermal histories predicted by the coupled model are compared to predictions of a standard enthalpy-method model in which the temperature dependence of the latent heat release, Λ(T) is an explicit function adapted from the water-NaCl phase diagram, and phase change is not rate-limited by microscale biophysical processes (i.e., an uncoupled approach). The results for both models are very similar; this suggests that the microscale biophysical processes which occur in the chosen biological tissues during freezing do little to limit the rate at which phase change occurs. Additional simulations suggest that the predicted macroscale thermal history results are not significantly affected (<2 percent variation) even with significantly altered biophysical parameters (i.e., a factor of 100 times lower or higher), as long as the magnitude of the latent heat is constant.
Error Model and Accuracy Analysis of a Six-DOF Stewart Platform
Authors: Wang Shih-Ming , Ehmann Kornel F.
Published: July 2002

Precision machining operations necessitate highly accurate, rigid, and stable machine-tool structures. In response to this need, parallel architecture machines, based on the concepts of the Stewart Platform, are emerging. In this paper, considering major inaccuracy factors related to the manufacture, geometry, and kinematics, of such machines, first and second order error models are presented, and followed by a comparative assessment of these models in conjunction with illustrative examples. Furthermore, in order to understand the character and propagation of errors of 6-DOF Stewart Platform based machine tools, sensitivity analysis is adopted to describe the contribution of each error component to the total position and orientation error of the mechanism. An automated error analysis system that computes and graphically depicts the error distributions throughout the workspace along with the results of sensitivity analysis is developed and demonstrated.
Non-Equilibrium Phase Change in Metal Induced by Nanosecond Pulsed Laser Irradiation
Authors: Xu Xianfan , Willis David A.
Published: July 2002

Materials processing using high power pulsed lasers involves complex phenomena including rapid heating, superheating of the laser-melted material, rapid nucleation, and phase explosion. With a heating rate on the order of 109K/s or higher, the surface layer melted by laser irradiation can reach a temperature higher than the normal boiling point. On the other hand, the vapor pressure does not build up as fast and thus falls below the saturation pressure at the surface temperature, resulting in a superheated, metastable state. As the temperature of the melt approaches the thermodynamic critical point, the liquid undergoes a phase explosion that turns the melt into a mixture of liquid and vapor. This article describes heat transfer and phase change phenomena during nanosecond pulsed laser ablation of a metal, with an emphasis on phase explosion and non-equilibrium phase change. The time required for nucleation in a superheated liquid, which determines the time needed for phase explosion to occur, is also investigated from both theoretical and experimental viewpoints.
Heat Transfer in Nanostructures for Solid-State Energy Conversion
Authors: Chen G. , Shakouri A.
Published: July 2002

Solid-state energy conversion technologies such as thermoelectric and thermionic refrigeration and power generation require materials with low thermal conductivity but good electrical conductivity and Seebeck coefficient, which are difficult to realize in bulk semiconductors. Nanostructures such as superlattices, quantum wires, and quantum dots provide alternative approaches to improve the solid-state energy conversion efficiency through size and interface effects on the electron and phonon transport. In this review, we discuss recent research and progress using nanostructures for solid-state energy conversion. The emphasis is placed on fundamental issues that distinguish energy transport and conversion between nanoscale and macroscale, as well as heat transfer issues related to device development and property characterization.
Available Energy—Part II: Gibbs Extended
Authors: Gaggioli Richard A. , Paulus, David M.
Published: July 2002

Since Gibbs, representations with formulas have been developed and are common, for the “available energy of body and medium.” Gaggioli has developed formulas which are more general, to represent “the available energy of the body (alone)” and to assign an exergy to subsystems of the body as a measure of each subsystem’s contribution to the available energy. In contrast to the available energy, exergy is an additive property, so that balance equations can be written. Moreover, the formulas are independent from any “medium,” which is important both theoretically and practically—because of its relevance to proper selection of “the dead state.” In Part II, these issues are discussed and extended. In the context of Gibbs’ “available energy of the body,” Gaggioli’s development of exergy for subsystems of the body without any reference to a “medium” are reviewed. It is illustrated that the concept of “constraints” underlies available energy, equilibrium and stability, and thermostatic property relations. Furthermore, it is argued that the “availability” and “capacity” concepts of Gibbs are all equivalent to each other. In turn, because of interconvertability, it is shown that available energy is something more fundamental than “maximum useful work.”
A New Device for Measuring the Viscoelastic Properties of Hydrated Matrix Gels
Authors: Parsons Jeffrey W. , Coger Robin N.
Published: July 2002

Determinations of the viscoelastic properties of extracellular matrices (ECMs) are becoming increasingly important for accurate predictive modeling of biological systems. Since the interactions of the cells with the ECM and surrounding fluid (e.g., blood, media) each affect cell behavior; it is advantageous to evaluate the ECM’s material properties in the presence of the hydrating fluid. Conventional rheometry methods evaluate the bulk material properties of gel materials while displacing the hydrating liquid film. Such systems are therefore nonideal for testing materials such as ECMs, whose properties change with dehydration. The new, patent pending, piezoelectrically actuated linear rheometer is designed to eliminate this problem. It uses a single cantilever to apply an oscillating load to the gel and to sense the gel’s deflection. Composed of two thin film piezopolymer layers, the cantilever uses one layer as the actuator, and the second piezopolymer layer to measure the lateral movement of its attached probe. The viscoelastic nature of the ECM adds stiffness and damping to the system, resulting in the attenuation and phase shift of the sensor’s output voltage. From these parameters, the ECM’s shear storage and loss moduli are then determined. Initial tests on the BioMatrix I and type I collagen ECMs reveal that the first prototype of the piezoelectrically actuated linear rheometer is capable of accurately determining the trend and order of magnitude of an ECM’s viscoelastic properties. In this paper, details of the rheometer’s design and operating principles are described.
A Dynamical Systems Approach to Damage Evolution Tracking, Part 1: Description and Experimental Application
Authors: Chelidze David , Cusumano Joseph P. , Chatterjee Anindya
Published: July 2002

In this two-part paper we present a novel method for tracking a slowly evolving hidden damage process responsible for nonstationarity in a fast dynamical system. The development of the method and its application to an electromechanical experiment is the core of Part 1. In Part 2, a mathematical model of the experimental system is developed and used to validate the experimental results. In addition, an analytical connection is established between the tracking method and the physics of the system based on the idea of averaging and the slow flow equations for the hidden process. The tracking method developed in this study uses a nonlinear, two-time-scale modeling strategy based on the delay reconstruction of a system’s phase space. The method treats damage-induced nonstationarity as evolving in a hierarchical dynamical system containing a fast, directly observable subsystem coupled to a slow, hidden subsystem. The utility of the method is demonstrated by tracking battery discharge in a vibrating beam system with a battery-powered electromagnetic restoring force. Applications to systems with evolving material damage are also discussed.
Falling Film Transitions on Plain and Enhanced Tubes
Authors: Roques J. F. , Dupont V. , Thome J. R.
Published: July 2002

In falling film heat transfer on horizontal tube bundles, liquid flow from tube to tube occurs as a falling jet that can take on different flow modes. At low flow rates, the liquid film falls as discrete droplets. At higher flow rates, these droplets form discretely spaced liquid columns. At still higher flow rates, the film falls as a continuous sheet of liquid. Predicting the flow transitions between these flow modes is an essential step in determining the heat transfer coefficient for the particular flow mode, whether for a single phase process or for falling film condensation or evaporation. Previous studies have centered mostly on falling films on plain tube arrays. The objective of the present study is to extend the investigation to tubes with enhanced surfaces: a low finned tube, an enhanced boiling tube and an enhanced condensation tube. The effect of tube spacing on flow transition has also been investigated. The test fluids were water, glycol and a glycol-water mixture. The adiabatic experimental results show that the flow mode transition thresholds for the enhanced boiling tube are very similar to those of the plain tube while the fin structure of the other two enhanced tubes can significantly shift their transition thresholds.
The Mechanics and Impact of Hygroscopic Swelling of Polymeric Materials in Electronic Packaging
Authors: Wong E. H. , Rajoo R. , Koh S. W. , Lim T. B.
Published: July 2002

A reliable technique for characterizing the hygroscopic swelling of materials has been developed and used to characterize a number of packaging materials. Using these data, hygroscopic stress modeling were performed. The hygroscopic stress induced through moisture conditioning was found to be significant compared to the thermal stress during solder reflow. Hygroscopic stress in over-molded wire bond PBGA and molded Flip Chip PBGA was found to be 1.3 times to 1.5 times that of thermal stress. Hygroscopic swelling of the underfill in FCPBGA was found to be the main failure driver during autoclave test. Autoclave performance of FCPBGA package assembled with different underfills and chips were analyzed. Excellent correlation was found between autoclave performance and the hygroscopic swelling characteristics of the underfills.
Hydrodynamic Design of Pump Diffuser Using Inverse Design Method and CFD
Authors: Goto Akira , Zangeneh Mehrdad
Published: July 2002

A new approach to optimizing a pump diffuser is presented, based on a three-dimensional inverse design method and a Computational Fluid Dynamics (CFD) technique. The blade shape of the diffuser was designed for a specified distribution of circulation and a given meridional geometry at a low specific speed of 0.109 (non-dimensional) or 280 (m3/min, m, rpm). To optimize the three-dimensional pressure fields and the secondary flow behavior inside the flow passage, the diffuser blade was more fore-loaded at the hub side as compared with the casing side. Numerical calculations, using a stage version of Dawes three-dimensional Navier-Stokes code, showed that such a loading distribution can suppress flow separation at the corner region between the hub and the blade suction surface, which was commonly observed with conventional designs having a compact bowl size (small outer diameter). The improvements in stage efficiency were confirmed experimentally over the corresponding conventional pump stage. The application of multi-color oil-film flow visualization confirmed that the large area of the corner separation was completely eliminated in the inverse design diffuser.
Generation and Forward Displacement Analysis of RP_R-PR-RP_R Analytic Planar Parallel Manipulators
Authors: Kong Xianwen , Gosselin Cle´ment M.
Published: July 2002

Analytic manipulators are manipulators for which a characteristic polynomial of fourth degree or lower can be obtained symbolically. Six types of RP_R-PR-RP_R analytic planar parallel manipulators (APPMs) are first generated using the component approach and the method based on the structure of the univariate equation. Of the six types, four are composed of Assur II kinematic chains while the other two are composed of Assur III kinematic chains. The forward displacement analysis (FDA) of two types of RP_R-PR-RP_R APPMs composed of Assur III kinematic chains is then performed. The FDA of each of the two types of APPMs composed of Assur III kinematic chains is reduced to the solution of a univariate cubic equation and a quadratic equation in sequence. It is also proven that the maximum number of real solutions to the FDA is 4 for the RP_R-PR-RP_R planar parallel manipulator with one aligned platform and one orthogonal platform. Examples with 4 real solutions for the RP_R-PR-RP_R planar parallel manipulator with one aligned platform and one orthogonal platform or 6 real solutions for the RP_R-PR-RP_R planar parallel manipulator with two aligned platforms are given at the end of this paper.
Fast Control of Linear Systems Subject to Input Constraints
Authors: Larsson P. Tomas , Ulsoy A. Galip
Published: July 2002

Efficient design of high performance automatic control systems is extremely important for high technology systems. To get the best hardware cost-to-performance ratio, it is desirable to design a controller that takes full advantage of actuator capabilities, but this can lead to nonlinear behavior due to actuator saturation. The saturation nonlinearities in the system may have severe effects on system performance due to, for example, integrator windup. In this paper, a new design method is presented based on Lyapunov stability theory. By incorporating the actuator constraints directly in the design method, better utilization of the available control effort can be ensured in achieving desired system behavior. [S0022-0434(00)01801-3]
Robust Input Shaper Control Design for Parameter Variations in Flexible Structures
Authors: Pao Lucy Y. , Lau Mark A.
Published: July 2002

Input shaping has been shown to yield good performance in the control of flexible structures while being insensitive to modeling errors. However, previous studies do not take into account the distributions of the parameter variations. We develop a new input shaping method that allows the ranges of system parameter values to be weighted according to the expected modeling errors. Comparisons with previously proposed input shaper designs are presented to illustrate the qualities of the new input shaper design method. These new shapers will be shown to have better robustness under uncertainty in structural parameters and shorter shaper lengths for lightly damped systems. [S0022-0434(00)02201-2]
Experimental Identification of Dynamic Parameters of Rolling Element Bearings in Machine Tools
Authors: Shamine D. M. , Hong S. W. , Shin Y. C.
Published: July 2002

In-situ identification is essential for estimating bearing joint parameters involved in spindle systems because of the inherent interaction between the bearings and spindle. This paper presents in-situ identification results for rolling element bearing parameters involved in machine tools by using frequency response functions (FRF’s). An indirect estimation technique is used for the estimation of unmeasured FRF’s, which are required for identification of joint parameters but are not available. With the help of an index function, which is devised for indicating the quality of estimation or identification at a particular frequency, the frequency region appropriate for identification is selected. Experiments are conducted on two different machine tool spindles. Repeatable and accurate joint coefficients are obtained for both machine tool systems. [S0022-0434(00)02501-6]
Repetitive Control for Asymptotic Tracking of Periodic Signals With an Unknown Period
Authors: Tsao Tsu-Chin , Qian and Yao-Xin , Nemani Mahadevamurty
Published: July 2002

Repetitive control schemes for asymptotic tracking and disturbance rejection of periodic signals with an unknown period are presented. A sampled data recursive scheme for identifying the period of a periodic signal with a resolution finer than the sampling interval is presented. Discrete-time self-tuning repetitive controllers, which adapt both the periodic signal period and sampling interval, are proposed based on the period identification scheme. The fine adaptation of the controller sampling interval makes the identified signal period an exact integer multiples of the controller sampling interval and renders a superior tracking performance than that of the conventional fixed sampling interval repetitive controllers. Experimental results on a linear motion system are presented to demonstrate the effectiveness of the proposed control schemes. [S0022-0434(00)01402-7]
Accounting for Elastic Energy Storage in McKibben Artificial Muscle Actuators
Authors: Klute Glenn K. , Hannaford Blake
Published: July 2002

The McKibben artificial muscle is a pneumatic actuator whose properties include a very high force to weight ratio. This characteristic makes it very attractive for a wide range of applications such as mobile robots and prosthetic appliances for the disabled. In this paper, we present a model that includes a nonlinear, Mooney–Rivlin mathematical description of the actuator’s internal bladder. Experimental results show that the model provides improvement in the ability to predict the actuator’s output force. However, a discrepancy between model and experiment, albeit smaller than previous models, still exists. A number of factors are identified that may be responsible for this discrepancy. [S0022-0434(00)00902-3]
Sodium Silicate Based Thermal Interface Material for High Thermal Contact Conductance
Authors: Xu Yunsheng , Luo Xiangcheng , Chung D. D. L.
Published: July 2002

Sodium silicate based thermal interface pastes give higher thermal contact conductance across conductor surfaces than polymer based pastes and oils, due to their higher fluidity and the consequent greater conformability. Addition of hexagonal boron nitride particles up to 16.0 vol. percent further increases the conductance of sodium silicate, due to the higher thermal conductivity of BN. However, addition beyond 16.0 vol. percent BN causes the conductance to decrease, due to the decrease in fluidity. At 16.0 vol. percent BN, the conductance is up to 63 percent higher than those given by silicone based pastes and is almost as high as that given by solder. Water is almost as effective as sodium silicate without filler, but the thermal contact conductance decreases with time due to the evaporation of water. Mineral oil and silicone without filler are much less effective than water or sodium silicate without filler. [S1043-7398(00)00402-3]
Solving the Inverse Dynamics of a Stewart-Gough Manipulator by the Principle of Virtual Work
Authors: Tsai Lung-Wen
Published: July 2002

This paper presents a systematic methodology for solving the inverse dynamics of a Stewart-Gough manipulator. Based on the principle of virtual work and the concept of link Jacobian matrices, a methodology for deriving the dynamical equations of motion is developed. It is shown that the dynamics of the manipulator can be reduced to solving a system of six linear equations in six unknowns. A computational algorithm for solving the inverse dynamics of the manipulator is developed and several trajectories of the moving platform are simulated. [S1050-0472(00)00401-3]