bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Chemistry and Characteristics Based Model for the Thermal Contact Resistance of Fluidic Interstitial Thermal Interface Materials
Authors: Prasher Ravi S.
Published: July 2002

Microprocessor powers are increasing at a phenomenal rate, which requires very small thermal resistance between the die (chip) and the ambient, if the current economical methods of conduction and convection cooling are to be utilized. A typical thermal solution in flip chip technology utilizes two levels of thermal interface materials: between the die and the heat spreader, and between the heat spreader and the heat sink. Phase change materials and thermal greases are among the most prominent interstitial thermal interface materials (TIM) used in electronic packaging. These TIMs are typically polymeric matrix loaded with highly conducting filler particles. The dwindling thermal budget has necessitated a better understanding of the thermal resistance of each component of the thermal solution. Thermal conductivity of these particle-laden materials is better understood than their contact resistance. A careful review of the literature reveals the lack of analytical models for the prediction of contact resistance of these types of interstitial materials, which possess fluidic properties. This paper introduces an analytical model for the thermal contact resistance of these types of interstitial materials. This model is compared with the experimental data obtained on the contact resistance of these TIMs. The model, which depends on parameters such as, surface tension, contact angle, thermal conductivity, roughness and pressure matches very well with the experimental data at low pressures and is still within the error bars at higher pressures.
Large Eddy Simulation of Turbulent Heat Transfer in an Orthogonally Rotating Square Duct With Angled Rib Turbulators
Authors: Murata Akira , Mochizuki Sadanari
Published: July 2002

Heat transfer in a rotating rib-roughened duct was simulated with a Lagrangian dynamic subgrid-scale model. The angled 60 deg rib induced a pair of strong vortices in the stationary condition, and the heat transfer and the friction factor were larger than the 90 deg rib case. In the rotating condition, the high heat transfer areas at the midpoint between ribs and in front of the rib were observed only on the trailing wall. The friction factor and overall Nusselt number were decreased by the duct rotation for 60 deg rib case, although they were increased for 90 deg rib case.
Experimental and Numerical Study of Turbulent Heat Transfer in Twisted Square Ducts
Authors: Wang Liang-Bi , Tao Wen-Quan , Wang Qiu-Wang , He Ya-Ling
Published: July 2002

This paper describes the experimental and numerical study of three mildly twisted square ducts (twisted uniform cross section square duct, twisted divergent square duct and twisted convergent square duct). Experiments are conducted for air with uniform heat flux condition. Measurements are also conducted for a straight untwisted square duct for comparison purpose. Numerical simulations are performed for three-dimensional and fully elliptic flow and heat transfer by using a body-fitted finite volume method and standard k−ε turbulence model. Both experimental and numerical results show that the twisting brings about a special variation pattern of the spanwise distribution of the local heat transfer coefficient, while the divergent and convergent shapes lead to different axial local heat transfer distributions. Based on the test data, the thermal performance comparisons are made under three constraints (identical mass flow rate, identical pumping power and identical pressure drop) with straight untwisted square duct as a reference. Comparisons show that the twisted divergent duct can always enhance heat transfer, the twisted convergent duct always deteriorates heat transfer, and the twisted constant cross section duct is somewhat in between.
Calculation of Unsteady Flows in Curved Pipes
Authors: Dwyer H. A. , Cheer A. Y. , Rutaganira T. , Shacheraghi N.
Published: July 2002

Highly unsteady three-dimensional flows in curved pipes with significant variation of flow geometry and flow parameters are studied. Using improvements in computational efficiency, detailed knowledge concerning flow structures is obtained. The numerical solutions of the Navier-Stokes equations have been obtained with a variation of the projection method, and the numerical method was enhanced by new algorithms derived from the physics of the flow. These enhancements include a prediction of the flow unsteady pressure gradient based on fluid acceleration and global pressure field corrections based on mass flow. This new method yields an order of magnitude improvement in the calculation’s efficiency, allowing the study of complex flow problems. Numerical flow simulations for oscillating flow cycles show that the curved pipe flows have a significant inviscid-like nature at high values of the frequency parameter. The shape of the velocity profiles is strongly influenced by the frequency parameter, whereas the influence of variations on the pipe cross-sectional area is shown to be rather weak. For large values of the frequency parameter the flow history strongly influences the low mass flow part of the cycle leading to highly unusual velocity profiles. The wall shear stress is studied for all the flows calculated. Our results show that wall shear stress is sensitive to area constrictions, the frequency parameter, as well as the shape of the entrance profile.
Motion-Dependent Fluid Force Coefficients for Tube Arrays in Crossflow
Authors: Chen S. S. , Srikantiah G. S.
Published: July 2002

Fluidelastic instability of tube arrays in crossflow is interesting academically and important in steam generators and heat exchangers. The key elements necessary to accurately predict fluidelastic instability of tube arrays in crossflow are motion-dependent fluid force coefficients. This paper presents several series of experiments that measure motion-dependent fluid forces for various tube arrays. Fluid damping and stiffness coefficients based on the unsteady flow theory were obtained as a function of reduced flow velocity, excitation amplitude, and Reynolds number, and the characteristics of motion-dependent fluid force coefficients were applied to provide some additional insights into fluidelastic instability.
The Combination of Attractive Regions and Pre-images in Motion Planning
Authors: Qiao H.
Published: July 2002

The general purpose of sensors is to obtain information on the system. However, in many cases, sensors cannot provide all the information on the system being controlled. On the other hand, the controller system does not need all the information in the process to guide the system into the goal, which provides the opportunity of utilizing simple sensors and then reducing the operational cost and time. The key point is that the information needed from the strategy should match the information which can be provided from the sensory signal. The difficulty left is due to the dependence between the sensor selection and strategy investigation. In other words, the two issues, (a) how to select the sensors and (b) how to form the commanded action, depend on each other. Benefited from the pre-image concept proposed by Lozano-Perez, Mason and Taylor1 and the attractive region concept proposed in the author’s previous work (2000), a logical method to design the pre-image of the goal is presented in this paper. Then the requirement of sensory feedback and the design of commanded action are given. Within this principle, the strategies in the robotic assembly with force sensors are investigated and applied in experiments in the present paper. It should be noted that the robotic assembly plays an important role in manufacturing automation. Also the assembly strategy presented here can be used with any machine.
Discrete-Time Well-Conditioned State Observer Design and Evaluation
Authors: Huh Kunsoo , Jung Jongchul , Stein Jeffrey L.
Published: July 2002

Model-based monitoring systems based on state observer theory often have poor performance with respect to accuracy, bandwidth, reliability (false alarms), and robustness. The above limitations are closely related to the ill-conditioning factors such as transient characteristics due to unknown initial values and round-off errors, and steady-state accuracy due to plant perturbations and sensor bias. In this paper, by minimizing the effects of the ill-conditioning factors, a well-conditioned observer is proposed for the discrete-time systems. A performance index is determined to represent the quantitative effects of the ill-conditioning factors and two design methods are described for the well-conditioned observers. The estimation performance of the well-conditioned observers is verified in simulations where transient as well as steady-state error robustness to perturbations is shown to be better than or equal to Kalman filter performance depending on the nature of modeling errors. The estimation performance is also demonstrated on an experimental setup designed and built for this purpose.
Mixing Characteristics of Axisymmetric Free Jets From a Contoured Nozzle, an Orifice Plate and a Pipe
Authors: Mi J. , Nathan G. J. , Nobes D. S.
Published: July 2002

The differences in mixing performance between axisymmetric turbulent jets issuing from three common types of nozzle, viz. a contoured (or smooth contraction) nozzle, a sharp-edged orifice and a long pipe, are investigated. The investigation is carried out using both qualitative flow visualizations and quantitative measurements of the centerline passive temperature. It is revealed that the jet issuing from an orifice plate provides the greatest rate of mixing with ambient fluid, while the pipe jet has the lowest rate. Physical insight into the differences is explored using a planar imaging technique and measurements of power spectra of the fluctuating velocity.
On the Mathematical Description and Simulation of Turbulent Flow in a Porous Medium Formed by an Array of Elliptic Rods
Authors: Pedras Marcos H. J. , de Lemos Marcelo J. S.
Published: July 2002

Many engineering and environmental system analyses can benefit from appropriate modeling of turbulent flow in porous media. Through the volumetric averaging of the microscopic transport equations for the turbulent kinetic energy, k, and its dissipation rate, ε, a macroscopic model was proposed for such media (IJHMT, 44(6), 1081-1093, 2001). In that initial work, the medium was simulated as an infinite array of cylindrical rods. As an outcome of the volume averaging process, additional terms appeared in the equations for k and ε. These terms were here adjusted assuming now the porous structure to be modeled as an array of elliptic rods instead. Such an adjustment was obtained by numerically solving the microscopic flow governing equations, using a low Reynolds formulation, in the periodic cell composing the medium. Different porosity and Reynolds numbers were investigated. The fine turbulence structure of the flow was computed and integral parameters were presented. The adjusted model constant was compared to similar results for square and cylindrical rods. It is expected that the contribution herein provide some insight to modelers devoted to the analysis of engineering and a environmental systems characterized by a porous structure saturated by a fluid flowing in turbulent regime.
Role of Cryogenic Cooling on Cutting Temperature in Turning Steel
Authors: Dhar N. R. , Paul S. , Chattopadhyay A. B.
Published: July 2002

Application of conventional cutting fluids do not serve the purposes effectively particularly under high cutting velocity and feed. Besides, such cutting fluids pollute the environment in high production machining and grinding. Cryogenic cooling seemed to be quite effective in reducing the high cutting temperature which impairs product quality and reduces tool life. The present work deals with investigating the role of cryogenic cooling by liquid nitrogen jet on cutting temperature in turning plain carbon steel (C-40) under varying cutting velocity and feed. The experimental and computational results indicate that such cryogenic cooling enables substantial reduction in the cutting temperature depending upon the levels of the cutting velocity and feed and the cutting tool geometry. It was also noted that the chip formation and chip-tool interaction become more favorable and the cutting forces decreased to some extent when liquid nitrogen jet was employed. Therefore, it appears that cryogenic cooling, if properly employed, not only provides environment friendliness but can also improve the machinability characteristics.
Coupled Vibration of Microcantilever Array Induced by Airflow Force
Authors: Hosaka Hiroshi , Itao Kiyoshi
Published: July 2002

The coupled vibrations of microcantilevers induced by airflow were analyzed to facilitate the development of high-speed information and sensing devices that use microactuator arrays. Simple formulas, from which the vibrational coupling amplitude and damping ratio can be obtained, are derived by replacing the cantilevers with strings of spheres, solving Stokes equation, and combining this with an ordinary beam equation. The coupling amplitude was found to increase as the beam size, beam gap, internal friction, and the difference in the resonant frequencies of the beams decreased and the damping ratio increased as the beam size was reduced. The validity of the theory is verified with actual-size and enlarged model experiments.
Nonlinear Wave Calculations for Engineering Applications
Authors: Forristall George Z.
Published: July 2002

Waves in the ocean are nonlinear, random, and directionally spread, but engineering calculations are almost always made using waves that are either linear and random or nonlinear and regular. Until recently, methods for more accurate computations simply did not exist. Increased computer speeds and continued theoretical developments have now led to tools which can produce much more realistic waves for engineering applications. The purpose of this paper is to review some of these developments. The simplest nonlinearities are the second-order bound waves caused by the pairwise interaction of linear components of the wave spectrum. It is fairly easy to simulate the second-order surface resulting from those interactions, a fact which has recently been exploited to estimate the probability distribution of wave crest heights. Once the evolution of the surface is known, the kinematics of the subsurface flow can be evaluated reasonably easily from Laplace’s equation. Much of the bound wave structure can also be captured by using the Creamer transformation, a definite integral over the spatial domain which modifies the structure of the wave field at one instant in time. In some ways, the accuracy of the Creamer transformation is higher than second order. Finally, many groups have developed numerical wave tanks which can solve the nonlinear wave equations to arbitrary accuracy. The computational cost of these solutions is still rather high, but they can directly calculate potential forces on large structures as well as providing test cases for the less accurate, but more efficient, methods.
Limit-Load Analysis of Pipe Bends Under Out-of-Plane Moment Loading and Internal Pressure
Authors: Mourad Hashem M. , Younan Maher Y. A.
Published: July 2002

The purpose of this work is to study the load-carrying capacity of pipe bends, with different pipe bend factor h values, under out-of-plane moment loading; and to investigate the effect of internal pressure on the limit moments in this loading mode. The finite element method is used to model and analyze a standalone, long-radius pipe bend with a 16-in. nominal diameter, and a 24-in. bend radius. A parametric study is performed in which the bend factor takes ten different values between 0.0632 and 0.4417. Internal pressure is incremented by 100 psi for each model, until the limit pressure of the model is reached. The limit moments were found to increase when the internal pressure is incremented. However, beyond a certain value of pressure, the effect of pressure is reversed due to the additional stresses it engenders. Expectedly, increasing the bend factor leads to an increase in the value of the limit loads. The results are compared to those, available in the literature, of a similar analysis that treats the in-plane loading mode. Pipe bends are found to have the lowest load-carrying capacity when loaded in their own plane, in the closing direction. They can sustain slightly higher loads when loaded in the out-of-plane direction, and considerably higher loads under in-plane bending in the opening direction.
An Evaluation of EJMA Stress Calculations for Unreinforced Bellows
Authors: Becht, Charles
Published: July 2002

The existing, widely used charts and equations for evaluation of unreinforced bellows were evaluated by parametric elastic finite element analysis. The prediction of meridional bending stress due to pressure and displacement were found to be relatively accurate. However, the prediction of membrane stress was found to deviate significantly from the finite element results. The cause of this discrepancy was discovered and is described in this paper.
Automatic Assembly Feature Recognition and Disassembly Sequence Generation
Authors: Sung Raymond C. W. , Corney Jonathan R. , Clark Doug E. R.
Published: July 2002

This paper describes a system for the automatic recognition of assembly features and the generation of disassembly sequences. The paper starts by reviewing the nature and use of assembly features. One of the conclusions drawn from this survey is that the majority of assembly features involve sets of spatially adjacent faces. Two principle types of adjacency relationships are identified and an algorithm is presented for identifying assembly features which arise from “spatial” and “contact” face adjacency relationships (known as s-adjacency and c-adjacency respectively). The algorithm uses an octree representation of a B-rep model to support the geometric reasoning required to locate assembly features on disjoint bodies. A pointerless octree representation is generated by recursively sub-dividing the assembly model’s bounding box into octants which are used to locate: 1. Those portions of faces which are c-adjacent (i.e. they effectively touch within the tolerance of the octree). 2. Those portions of faces which are s-adjacent to a nominated face. The resulting system can locate and partition spatially adjacent faces in a wide range of situations and at different resolutions. The assembly features located are recorded as attributes in the B-rep model and are then used to generate a disassembly sequence plan for the assembly. This sequence plan is represented by a transition state tree which incorporates knowledge of the availability of feasible gripping features. By way of illustration, the algorithm is applied to several trial components
Large Eddy Simulation of a Flow Past a Free Surface Piercing Circular Cylinder
Authors: Kawamura T. , Mayer S. , Garapon A. , Sørensen L.
Published: July 2002

Interactions between surface waves and underlying viscous wake are investigated for a turbulent flow past a free surface piercing circular cylinder at Reynolds number Re=2.7×104 using large eddy simulation (LES). The computations have been performed for three Froude numbers Fr=0.2, 0.5 and 0.8 in order to examine the influence of the Froude number. A second-order finite volume method coupled with a fractional step method is used for solving the grid-filtered incompressible Navier-Stokes equations. The computational results are found to be in good agreement with the available experimental data. At low Froude numbers Fr=0.2 and 0.5, the amplitude of generated surface wave is small and the influence on the wake is not evident. On the other hand, strong wave-wake interactions are present at Fr=0.8, when the generated free surface wave is very steep. It is shown that structures of the underlying vortical flow correlate closely with the configuration of the free surface. Computational results show presence of a recirculation zone starting at the point where the surface slope changes discontinuously. Above this zone the surface elevation fluctuates intensively. The computed intensity of the surface fluctuation is in good agreement with the measurements. It is also shown that the periodic vortex shedding is attenuated near the free surface at a high Froude number. The region in which the periodic vortex shedding is hampered extends to about one diameter from the mean water level. It is qualitatively shown that the separated shear layers are inclined outward near the free surface due to the generation of the surface waves. This change in the relation between two shear layers is suggested to be responsible for the attenuation of the periodic vortex shedding.
Studies of Stick-Slip Friction, Presliding Displacement, and Hunting
Authors: Wu Ruh-Hua , Tung Pi-Cheng
Published: July 2002

This paper presents the studies of stick-slip friction, presliding displacement and its influence on hunting. Experimental studies reveal that presliding displacement could affect the stability of hunting. A modified Coulomb friction model integrating presliding displacement in the microsliding regime is proposed to demonstrate such effect. Finally, step responses obtained from experiments and from the modified model are compared. These comparisons yield the conclusion that the transition of friction between the sticking state and the sliding state is smooth and continuous, not abrupt. Such a smooth transition of friction is critical to the studies of systems performing high-speed cyclic motion.
The Duality in Spatial Stiffness and Compliance as Realized in Parallel and Serial Elastic Mechanisms
Authors: Huang Shuguang , Schimmels Joseph M.
Published: July 2002

Spatial elastic behavior is characterized by a 6×6 positive definite matrix, the spatial stiffness matrix, or its inverse, the spatial compliance matrix. Previously, the structure of a spatial stiffness matrix and its realization using a parallel elastic system have been addressed. This paper extends those results to the analysis and realization of a spatial compliance matrix using a serial mechanism and identifies the duality in spatial stiffness and compliance associated with parallel and serial elastic mechanisms. We show that, a spatial compliance matrix can be decomposed into a set of rank-1 compliance matrices, each of which can be realized with an elastic joint in a serial mechanism. To realize a general spatial compliance, the serial mechanism must contain joints that couple the translational and rotational motion along/about an axis. The structure of a spatial compliance matrix can be uniquely interpreted by a 6-joint serial elastic mechanism whose geometry is obtained from the eigenscrew decomposition of the compliance matrix. The results obtained from the analysis of spatial compliant behavior and its realization in a serial mechanism are compared with those obtained for spatial stiffness behavior and its realization in a parallel mechanism.
Nonstationary Velocity Profiles for Emergency Vehicles on Automated Highways
Authors: Toy Charmaine , Alvarez Luis , Horowitz Roberto
Published: July 2002

This paper explores the notion and usefulness of nonstationary velocity profiles for high priority emergency vehicle transit on automated highways. These profiles are intended for use in the link layer of the hierarchical control architecture defined by the California Partners for Automated Transit and Highways (PATH) program. A non-stationary velocity profile which can be used to circulate traffic around a faster moving emergency vehicle is introduced. The effects on traffic flow are illustrated. A traffic flow controller that sustains nonstationary velocity profiles on fully automated highways is designed. Controller stability is discussed stressing the usefulness of nonstationary velocity profiles in creating a moving area of low vehicle density. Simulation results obtained using SmartCap, a traffic flow simulation program, demonstrate the fast circulation of an emergency vehicle in AHS while high traffic flow is maintained.
Code Verification by the Method of Manufactured Solutions
Authors: Roache Patrick J.
Published: July 2002

Verification of Calculations involves error estimation, whereas Verification of Codes involves error evaluation, from known benchmark solutions. The best benchmarks are exact analytical solutions with sufficiently complex solution structure; they need not be realistic since Verification is a purely mathematical exercise. The Method of Manufactured Solutions (MMS) provides a straightforward and quite general procedure for generating such solutions. For complex codes, the method utilizes Symbolic Manipulation, but here it is illustrated with simple examples. When used with systematic grid refinement studies, which are remarkably sensitive, MMS produces strong Code Verifications with a theorem-like quality and a clearly defined completion point.
Volume of fluid interface reconstruction methods for multi-material problems
Authors: Benson David J
Published: July 2002

Volume of fluid interface reconstruction methods are used to resolve the interfaces between different materials in Eulerian and arbitrary Lagrangian Eulerian calculations. Their accuracy is critical to the overall accuracy of the calculation since the interfaces define the interactions between adjacent materials. The methods have evolved since the early 1960s, and the early criticisms of them no longer hold. In this review article, the differences between the methods and their relative strengths are reviewed, and 38 reference sources are used.
Prediction of Flow and Heat Transfer in Rotating Two-Pass Rectangular
Channels With 45-deg Rib Turbulators
Authors: Al-Qahtani Mohammad , Jang Yong-Jun , Chen Hamn-Ching , Han Je-Chin
Published: July 2002

Numerical predictions of three-dimensional flow and heat transfer are presented for a rotating two-pass rectangular channel with 45-deg rib turbulators and channel aspect ratio of 2:1. The rib height-to-hydraulic diameter ratio e/Dh is 0.094 and the rib-pitch-to-height ratio P/e is 10. Two channel orientations are studied: β=90deg and 135 deg, corresponding to the mid-portion and the trailing edge regions of a turbine blade, respectively. The focus of this study is twofold; namely, to investigate the effect of the channel aspect ratio and the channel orientation on the nature of the flow and heat transfer enhancement. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. The numerical results compare reasonably well with experimental data for both stationary and rotating rectangular channels with rib turbulators at Reynolds number (Re) of 10,000, rotation number (Ro) of 0.11 and inlet coolant-to-wall density ratio (Δρ/ρ) of 0.115.
Application of the finite element method to prediction of onset of delamination growth
Authors: Miravete Antonio , Jime´nez Miguel A
Published: July 2002

The present article is concerned with the application of the finite element method to the analysis of the onset of delamination growth in composites by means of the virtual crack closure technique (VCCT). The article reviews first the application of linear elastic fracture mechanics (LEFM) to the analysis of delamination, as well as the reasons why the VCC technique is the standard method of combining LEFM and the finite element method to predict onset of delamination growth. The article also reviews the different solutions proposed in the literature to deal with the oscillatory singularity associated with a crack between two dissimilar materials (as is the case for a delamination) and the practical details of the VCCT application in a general 3D analysis. Finally, the results of a numerical study of the mixed mode bending (MMB) interlaminar fracture test are shown. The study applies the concepts reviewed along the rest of this article and presents some practical recommendations for the analysis of a delamination front using finite elements. This review article includes 77 references.
MEMS-Micropumps: A Review
Authors: Nguyen Nam-Trung , Huang Xiaoyang , Chuan Toh Kok
Published: July 2002

Microfluidics has emerged from the MEMS-technology as an important research field and a promising market. This paper gives an overview on one of the most important microfluidic components: the micropump. In the last decade, various micropumps have been developed. There are only a few review papers on microfluidic devices and none of them were dedicated only to micropumps. This review paper outlines systematically the pump principles and their realization with MEMS-technology. Comparisons regarding pump size, flow rate, and backpressure will help readers to decide their proper design before starting a microfluidics project. Different pump principles are compared graphically and discussed in terms of their advantages and disadvantages for particular applications.
Predicting Mixing Volumes in Serial Transport in Pipelines
Authors: Rachid F. B. Freitas , de Araujo J. H. Carneiro , Baptista R. M.
Published: July 2002

This paper presents a model for predicting the contaminated mixing volume arising in pipeline batch transfers without physical separators. The proposed technique represents an improvement over the existing methods since it takes into account time-dependent flow rates and accurate concentration-varying axial dispersion coefficients. The governing equation of the model forms a nonlinear boundary-value problem that is solved by a finite element method coupled to the Newton’s method. A comparison among the theoretical predictions of this method, a field test, and other classical procedures show that the proposed method exhibits the best estimate over the whole range of admissible concentrations investigated.
Modeling and Analysis of the Effect of Fixture-Workpiece Conformability on Static Stability
Authors: Hurtado Jose´ F. , Melkote Shreyes N.
Published: July 2002

This paper presents a model for analyzing the effect of global and local conformability on fixture-workpiece system static stability. Global conformability is defined as the geometric similarity between a workpiece and the smallest envelope fit over all contacts. Two conformability metrics, C1 and C2, are introduced to quantify only global, and global plus local conformability, respectively. The model considers all stiffness components of the fixture-workpiece system, including workpiece bulk stiffness. The effect of both conformability metrics on fixture-workpiece static stability is analyzed by means of examples. These examples show that static stability can either increase or decrease with conformability depending on the position of the fixturing elements with respect to the line of action of the externally applied loads. The model is experimentally validated using a pin-array type flexible machining fixture.
Detailed Numerical and Experimental Investigation of Non-Isothermal
Sintering of Amorphous Polymer Material
Authors: Tarafdar R. M. , Bergman T. L.
Published: July 2002

Simulations and experiments are performed to investigate the coupled thermal and morphological response of polymer material during non-isothermal sintering. The experimental results are utilized to validate a numerical model that describes the response of the system. Predictions of the material expansion, its subsequent contraction due to sintering, and the temperature evolution are obtained and favorably compared with experimental results. Parametric simulations are performed to acquire additional insight into the dynamics of non-isothermal sintering while a relationship is established to describe the ratio of the sintering penetration depth to the thermal penetration depth and its dependence upon the boundary and initial temperatures.
Computation of Optimal Workpiece Orientation for Multi-axis NC Machining of Sculptured Part Surfaces
Authors: Radzevich Stephen P. , Goodman Erik D.
Published: July 2002

Optimal workpiece orientation for multi-axis sculptured part surface machining is generally defined as orientation of the workpiece so as to minimize the number of setups in 4-, 5- or more axis Numerical Control (NC) machining, or to allow the maximal number of surfaces to be machined in a single setup on a three-, four-, or five-axis NC machine. This paper presents a method for computing such an optimal workpiece orientation based on the geometry of the part surface to be machined, of the machining surface of the tool, and of the degrees of freedom available on the multi-axis NC machine. However, for cases in which some freedom of orientation remains after conditions for machining in a single setup are satisfied, a second sort of optimality can also be considered: finding an orientation such that the cutting condition (relative orientation of the tool axis and the normal to the desired part surface) remains as constant, at some optimal angle, as possible. This second form of optimality is obtained by choosing an orientation (within the bounds of those allowing a single setup) in which the angle between the neutral axis of the milling tool and the area-weighted mean normal to the part surface, at a “central” point with a normal in that mean direction, is zero, or as small as possible. To find this solution, Gaussian maps (GMap) of the part surfaces to be machined and the machining surface of the tool are applied. To our knowledge, we are the first [1] who have picked up this Gauss’ idea to sculptured part surface orientation problem and who have developed the general approach to solve this important engineering problem [2]. Later a similar approach was claimed by Gan [3]. By means of GMaps of these surfaces, the problem of optimal workpiece orientation can be formulated as a geometric problem on a sphere. The GMap on a unit sphere finds wide application for orientation of workpiece for NC machining, for probing on coordinate measuring machines, etc. GMaps are useful for selecting the type of cutting tool, its path, workpiece fixturing, and the type of NC machine (its kinematic capabilities). The primary process application addressed is 3- and 4-axis NC milling, although the techniques presented may be applied to machines with more general articulation. The influence of tool geometry is also discussed and incorporated within a constrained orientation algorithm. This paper covers the following topics: a) the derivation of the equations of the GMap of the part surface to be machined and the machining surface of the tool; b) calculation of the parameters of the weighted normal to the part surface; c) optimal part orientation on the table of a multi-axis NC machine; d) introduction of a new type of GMap for a sculptured part surface—its expandedGMapE; and e) introduction of a new type of indicatrix of a sculptured part surface and a particular cutting tool–the indicatrix of machinability.
Static, vibration, and buckling analyses and applications to one-sheet hyperboloidal shells of revolution
Authors: Krivoshapko SN
Published: July 2002

The principal achievements of science and engineering in the sphere of design, construction, and static, vibrational, and buckling analysis of thin-walled constructions and buildings in the shape of hyperbolic surfaces of revolution are summarized in this review article. These shells are useful as hyperbolic cooling towers, TV towers, reinforced concrete water tanks, and arch dams. They are also used as supports for electric power transmission lines and as high chimneys. Several public and industrial buildings having the hyperbolic form are described in the review. The basic results of theoretical and experimental investigations of stress-strain state, buckling, and vibration are summarized. The influence of temperature and moisture on the stress-strain state of the shells in question is also analyzed. This review article contains 261 references.
Self-Organization and Self-Similarity in Boiling Systems
Authors: Chai L. H. , Shoji M.
Published: July 2002

Boiling system is a typical open dissipative structure. Focusing on the investigation of boundary adjacent to heating plate surface in boiling system, nonlinear non-equilibrium statistical thermodynamics theory of open systems was originally constructed. The competitive bubble formation was realized by non-equilibrium phase transition caused by the interactions among active sites or bubbles. The “natural selection” among all possible sites was mathematically outlined. It was by the means of “natural selection” that a kind of self-organized and self-similar structure was formed. The present studies theoretically explained the experimental observations from other researchers, and gave more reasonable guidance of enhancing boiling heat transfer, such as by way of installing artificial cavities. Beyond the scope of boiling systems, the present studies not only have far-reaching theoretical implications on explaining time, life, thermodynamic, self-similar, fluctuation, order and chaos etc., but also can find many promising applications from new perspectives, such as wider industrial optimization, the recognitions of pattern and reproduction pattern of by computer etc.
Editorial
Authors: Guilak Farshid , Hung Clark T. , Vanderby, Ray
Published: July 2002

[S0148-0731(00)01403-5]
A Simplified Cartesian-Computed Torque Controller for Highly Geared Systems and Its Application to an Experimental Climbing Robot
Authors: Bevly David , Dubowsky Steven , Mavroidis Constantinos
Published: July 2002

A simplified Cartesian computed torque (SCCT) control scheme and its application to an experimental climbing robot named LIBRA is presented. SCCT control is developed exploiting some of the characteristics of highly geared mobile robots. The effectiveness of the method is shown by simulation and experimental results using the LIBRA robot. SCCT control is shown to have improved performance, over traditional Jacobian transpose control, for the LIBRA multilimbed robot. [S0022-0434(00)03501-2]
A Repetitive Learning Method Based on Sliding Mode for Robot Control
Authors: Liu T. S. , Lee W. S.
Published: July 2002

In order to make a robot precisely track desired periodic trajectories, this work proposes a sliding mode based repetitive learning control method, which incorporates characteristics of sliding mode control into repetitive learning control. The learning algorithm not only utilizes shape functions to approximate influence functions in integral transforms, but also estimates inverse dynamics functions based on integral transforms. It learns at each sampling instant the desired input joint torques without prior knowledge of the robot dynamics. To carry out sliding mode control, a reaching law method is employed, which is robust against model uncertainties and external disturbances. Experiments are performed to validate the proposed method. [S0022-0434(00)02001-3]
Robust Nonlinear Control of Parametric Uncertain Systems With Unknown Friction and Its Application to a Pneumatic Control Valve
Authors: Shen Tielong , Tamura Katsutoshi , Kaminaga Hiroshi , Henmi Noriaki , Nakazawa Toru
Published: July 2002

A robust nonlinear control approach is presented for parametric uncertain systems with unknown friction. First- and second-order systems are considered, respectively. A model reference controller is developed such that the tracking error is bounded and converges to zero in the presence of the parameter uncertainty and the unknown friction. Then, the controller is extended to general case with any order. To design the controller, exact friction force is not required, only the upper bound for the level. Lyapunov’s direct method is used to prove robust global convergence of the tracking error. Finally, experimental results are given by applying the proposed controller to a pneumatic control valve. [S0022-0434(00)01802-5]
Multiaxial Cyclic Ratcheting in Coiled Tubing—Part II: Experimental Program and Model Evaluation
Authors: Rolovic Radovan , Tipton Steven M.
Published: July 2002

An experimental program was conducted to evaluate the plasticity model proposed in a separate paper (Part I). Constant pressure, cyclic bend-straighten tests were performed to identify material parameters required by the analytical model. Block pressure, bend-straighten tests were conducted to evaluate the proposed model. Experiments were performed on full-size coiled tubing samples using a specialized test machine. Two commonly used coiled tubing materials and four specimen sizes were subjected to load histories consisting of bending-straightening cycles with varying levels of internal pressure. It was observed that cyclic ratcheting rates can be reversed without reversing the mean stress, i.e., diametral growth of coiled tubing can be followed by diametral shrinkage even when the internal pressure is kept positive, depending on the loading history. This material behavior is explained in the context of the new theory. The correlation between the predictions and the test data is very good. [S0094-4289(00)00502-8]
Temperature-Dependent Popcorning Analysis of Plastic Ball Grid Array Package During Solder Reflow With Fracture Mechanics Method
Authors: Lau John H. , Lee S. W. Ricky
Published: July 2002

The popcorning effect of plastic ball grid array (PBGA) packages is analyzed using the method of fracture mechanics. The following three specific problems are studied: (1) crack initiation in the die attach of the package, (2) crack growth in the die attach, and (3) crack growth at the interface between the solder mask and copper. Two different methods (crack tip opening displacement and virtual crack closure technique) are used to determine the crack-tip parameters such as the strain energy release rate, stress intensity factors, and phase angle for different crack lengths and temperatures. [S1043-7398(00)00401-1]
Thermal Management Enhancement for GaAs Devices Using CVD Diamond Heat Spreaders in a Plastic Package Environment
Authors: Fabis Philip M. , Windischmann Henry
Published: July 2002

Long term package reliability is becoming an increasing concern as IC clock speeds and power densities increase while simultaneously the package foot print decreases. Significant contributors to increasing the reliability and performance of plastic packages are reducing the package/junction temperature Tj and improving the integrity of the interfaces between the encapsulating polymer and the constituent package materials. CVD diamond, with its superior thermal conductivity, low density and high electrical resistivity offers an attractive alternative to traditional metal heat spreader materials to insuring a low junction temperature and therefore long time between failures. Considering these goals and the ubiquitous performance, reliability, and economic requirements, GaAs devices were encapsulated in a plastic package with CVD diamond substrates as the thermal management platform. Both GaAs flip-chip with polymer underfill and conventional face up chip-wire configurations were evaluated. This paper will highlight the effect of chemical termination of the CVD diamond surface on encapsulant polymer adhesion using x-ray photoelectron spectroscopy, surface energy measurements, and boiling water immersion/peeling tests. Additionally, the enhanced thermal and reliability (mechanical/environmental) performance of plastic packaged GaAs devices using “optimally terminated” CVD diamond will be discussed. [S1043-7398(00)00802-1]
Flow Analysis in a Chip Cavity During Semiconductor Encapsulation
Authors: Han S. , Wang K. K.
Published: July 2002

In this paper, methods to analyze the flow during semiconductor chip encapsulation have been developed. A numerical method is used for the flow analysis in the chip cavity. In this study, for accurate analysis of flow in the chip cavity, models for the cross flow through the leadframe openings have been developed. The models have been verified by comparing with two experiments. In the first experiment, clear polymer and transparent mold have been used for the visualization of flow in a cavity with a leadframe. In the next experiment, actual epoxy molding compound together with an industrial encapsulation process have been used to observe the melt-front advancement shapes. The calculated and experimental results show good agreement. [S1043-7398(00)00902-6]
Advances in Oxide-Oxide CMC
Authors: Jurf Robert A. , Butner Steven C.
Published: July 2002

Recent advances in COI’s oxide–oxide CMC materials will be presented including basic processing steps, updated material properties, and fabrication techniques. Material properties of COI’s alumino-silicate system reinforced with various oxide fabrics will be compared, along with progress in developing a 1200°C oxide matrix system for future turbine system applications. Examples of fabricated hardware, including a subscale combustion liner, will be shown. Recent test and evaluation data will be provided. [S0742-4795(00)01802-0]
Status of Catalytic Combustion R&D for the Department of Energy Advanced Turbine Systems Program
Authors: Fant D. B. , Jackson G. S. , Karim H. , Newburry D. M. , Dutta P. , Smith K. O. , Dibble R. W.
Published: July 2002

This paper discusses some of the advanced concepts and research and development associated with implementing catalytic combustion to achieve ultra-low-NOx emissions in the next generation of land-based gas turbine engines. In particular, the paper presents current development status and design challenges being addressed by Siemens Westinghouse Power Corp. for large industrial engines (>200 MW) and by Solar Turbines for smaller engines (<20 MW) as part of the U.S. Department of Energy’s (DOE) Advanced Turbine Systems (ATS) program. Operational issues in implementing catalytic combustion and the current needs for research in catalyst durability and operability are also discussed. This paper indicates how recent advances in reactor design and catalytic coatings have made catalytic combustion a viable technology for advanced turbine engines and how further research and development may improve catalytic combustion systems to better meet the durability and operability challenges presented by the high-efficiency, ultra-low emissions ATS program goals. [S0742-4795(00)01502-7]
Characteristics of Shallow Turbulent Near Wakes at Low Reynolds Numbers
Authors: Balachandar Ram , Ramachandran Shyam , Tachie Mark F.
Published: July 2002

The present study deals with the noninvasive measurement of both velocity and concentration in the near region of shallow turbulent wakes using a laser-Doppler anemometer and a video-imaging technique. A 40 mm wide flat plate placed normal to the flow is used as the wake generator. The flow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallow. Tests were conducted at two depths of flow (h=20 and 40 mm) and the boundary layer thickness of the approaching flow is comparable to the depth. The Reynolds number of the flow based on the approaching freestream boundary layer momentum thickness varies from 180 to 400, while, the Reynolds number based on the test body width was maintained nearly constant (≈4000). Measurements were carried out at three axial stations (2.5, 5, and 10 plate widths) downstream of the bluff body. At each axial station, the velocity measurements were carried at distances of h/4,h/2, and 3h/4 from the channel bottom and spanning the cross section of the wake. Appropriate length and velocity scales are identified to characterize the wake. The axial variation of the shallow wake half-width based on both the lateral velocity profile and the lateral concentration profile is also obtained. A shear parameter is introduced to analyze the relative effects of transverse shear and bed friction. [S0098-2202(00)01802-2]