bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Convection From a Pair of Parallel Horizontal Circular Cylinders Set in Free Air With Different Alignments
Authors: Cianfrini Claudio , Corcione Massimo , Habib Emanuele
Published: April 2008

Steady laminar free convection in air from a pair of parallel horizontal cylinders set in a plane inclined with respect to the gravity vector, with the horizontal and vertical positions as special cases, is studied numerically. A specifically developed computer-code based on the SIMPLE-C algorithm is used for the solution of the dimensionless mass, momentum, and energy transfer governing equations. Results are presented for different values of the center-to-center cylinder spacing from 1.4 up to 10 diameters, the tilting angle of the array from 0° to 90°, and the Rayleigh number based on the cylinder-diameter in the range between 103 and 107.
Heat Transfer Features of a Horizontal Slot Jet Impinging in Mixed Convection
Authors: Corcione Massimo , Habib Emanuele , Ruocco Gianpaolo
Published: April 2008

The mutual interactions occurring between a laminar confined slot jet impinging on a isothermal vertical wall and the natural upward draft promoted by the same target wall, as well as their effects on the local and average heat transfer rates at the target surface, are studied numerically. A specifically developed computer code based on the SIMPLE-C algorithm is used for the solution of the governing equations. Results are presented for different values of the Reynolds number based on the nozzle width in the range between 0 and 400, the Grash of number based on the target wall length in the range between 0 and 108, and a complete range of geometry parameters (jet nozzle width, length of the target wall, and nozzle-to-target spacing).
Heat Transfer Characteristics of Oscillating Flow Through Highly Porous Medium
Authors: Jin L. W. , Leong K. C.
Published: April 2008

Heat transfer in porous media has been investigated extensively with the motivation of enhancing heat removal in electronics cooling applications. Many investigations have been conducted on heat transfer in a channel filled with porous media. However, steady flow through a porous channel still yield a higher temperature difference along the flow direction. It is conceivable that oscillating flow through a porous channel will produce a more uniform temperature distribution due to the two thermal entrance regions of oscillating flow. As compared to a porous channel packed with metal particles, spheres or woven-screens, the highly porous open-cell metal foam possesses a different configuration. The polyhedral pore and reticulated ligament structures provide the extremely large fluid-to-solid contact surface area and tortuous coolant flow path inside the metal foam, which could increase dramatically the overall heat transfer rate. A survey of the literature shows that heat transfer in open-cell metal foam were mostly investigated under steady flow condition. Published literature on heat transfer in metal foams subjected to oscillating flow is scarce. This paper presents both experimental and numerical investigations on the heat transfer characteristics for oscillating flow through highly porous medium. Experiments were carried out to study the effect of the oscillatory frequency on the heat transfer in metal foams with various pore densities. The results show that the local Nusselt number increases with the kinetic Reynolds number. Higher total heat transfer rates for oscillating flow can be obtained by using high pore density metal foam. The numerical simulation is focused on the study of the variations of the transient temperature and Nusselt number at different locations in the porous channel during a complete cycle. The numerical results show that the profile of the transient temperature decreases with the increase of the distance along the vertical direction and the variation of the instantaneous Nusselt number at entrance region is more significant than that at the location close to the center of the porous channel. It is also found that the two-dimensional temperature distributions in the numerical domain are symmetric about the center of the channel at the cycle-steady state. The comparison shows that the results obtained by the simulation are in reasonably good agreement with the experimental data.
Thermal Analysis of Plate Condensers in Presence of Flow Maldistribution Using Refrigerant R134a
Authors: Bobbili P. R. , Sunden B. , Das S. K.
Published: April 2008

Flow maldistribution in plate heat exchangers causes deterioration of both thermal and hydraulic performance. The situation becomes more complicated for two phase flows during condensation where uneven distribution of the liquid to the channels reduces heat transfer due to high liquid flooding. The present study evaluates the thermal performance of falling film plate condensers with flow maldistribution from port to channel considering the heat transfer coefficient inside the channels as a function of channel flow rate. A generalized mathematical model has been developed to investigate the effect of maldistribution on the thermal performance as well as the exit vapor quality of a refrigerant, namely R-134a. A wide range of parameters are studied and these show the effects of the mass flow rate ratio of cold fluid (water) and two-phase refrigerant fluid, flow configuration, number of channels and correlation for the heat transfer coefficient. The analysis presented here also suggests an improved method for heat transfer data analysis for plate condensers.
Reliability Prediction of Remanufactured Product: A Welding Repair Process Case Study
Authors: Esterman Marcos , Gerst Philip , DeBartolo Elizabeth , Haselkorn Michael H.
Published: April 2008

Many experts agree that effective management of system reliability and reliability validation during product development is a key to achieve superior time to market and life cycle quality. However, reliability performance prediction is a common problem faced by all product developers and it is usually a difficult task. A related problem is to determine the reliability performance of a remanufactured product. Clearly, the remanufacturer would like to know the expected reliability of their product before entering it into service, but unlike an original manufacturer, they will typically have much less information available to them. In this paper, a general framework for reliability prediction in a remanufacturing environment is proposed. A case study of a remanufactured engine cylinder head that has had a fatigue crack repaired by a welding process will be presented in order to illustrate the process. The approach combines the use of Failure Modes and Effects Analysis (FMEA), Experimental Model Building, Monte Carlo Simulation and Linear Elastic Fracture Mechanics (LEFM) to generate a reliability estimate. The FMEA and physical modeling will be used to generate a model that relates the welding process control parameters to the fatigue performance of the test specimens. Monte Carlo Simulation techniques and LEFM will build on the above model to relate the process control parameters to the reliability performance. The paper concludes by discussing the utility of such a model and approach, and presents the future research agenda.
A New Multiple Point Asperity Model for Contact Between Nominally Flat Surfaces
Authors: Hariri A. , Zu J. W. , Ben Mrad R.
Published: April 2008

For several decades, asperities of nominally flat rough surfaces were considered to be points higher than their immediate neighbors. Recently, it has been recognized that this model is inadequate. To address the issue, a new multiple point asperity model, called η-point asperity model, is introduced in this paper. In the new model, asperities are composed of η neighboring sampled points with η-2 middle points being above a certain level. When the separation between two surfaces decreases, new asperities with higher number of sample points, η, will come into existence. Based on the above model, the height and curvature of η-point asperities are defined and their distributions are found. The model is developed for Gaussian surfaces and for the general case of autocorrelation function (ACF). As a case study, the exponential ACF is applied to the new model, which is shown to produce remarkably good agreement with measurements from real and simulated surfaces.
Radial Ultra-Micro Wave Rotors (UµWR): Design and Simulation
Authors: Iancu Florin , Piechna Janusz , Mu¨ller Norbert
Published: April 2008

It has been shown that the wave rotor technology has the potential of improving the performance of gas turbine cycles. Moreover the radial wave rotor is an additional innovation for this technology. Unlike the commercialized axial-flow wave rotor (Comprex®), a radial one has the benefit of using centrifugal forces to improve the compression process or flow scavenging. The geometry of the rotor is much simpler and is ideal for microfabrication, which is relying mainly on two-dimensional processes to create three-dimensional features. This paper is presenting several radial ultra-micro wave rotors (UμWR) configurations and numerical analysis of these rotors. In a radial placement, the wave rotor has four possible configurations: two - general configuration, through-flow and reverse-flow, and each of these could have the low pressure air port positioned at inside or outside of the rotor. Results have been obtained using FLUENT, a Computational Fluid Dynamics (CFD) commercial code. The vast information about the unsteady processes occurring during simulation is visualized.
A Web Services Approach for Sharing Remote Laboratory Resources
Authors: Li Yaoye , Esche Sven K. , Chassapis Constantin
Published: April 2008

Because of their promise of significant benefits to all stakeholders in the laboratory education process, an increasing number of shared remotely accessible student laboratory resources are being developed by many educational institutions around the world. These resources include both remote laboratories, which are based on actual experimental devices as well as virtual laboratories, which represent software simulations of experiments. Web services are becoming more and more popular as an efficient technology for sharing distributed applications and structured information. In this article, we will propose a Web services based approach for the development and implementation of a scalable platform for providing a large variety of educational laboratory experiences to widely dispersed student audiences. We will present the general methodology for locating and utilizing distributed remote laboratory resources based on this Web services oriented system architecture. In particular, we will describe the overall system architecture, the design of the communication between the various system components and system users, the approach taken in managing the dynamic set of distributed resources in an efficient manner, the software architecture employed in searching for specific laboratory resources with certain functionalities as well as some challenges arising in the design and implementation of such a system.
Six Sigma Methodology for Sensor Package Evaluation
Authors: Subramanian Kanakasabapathi , Strick Jeffrey E. , Sitaraman Ram , Craddock Russell W. , Kinnell Peter K. , Sathe Abhijeet
Published: April 2008

Six sigma methods were used to evaluate the effect of package design on the performance of an oil-isolated resonant pressure sensor. The sensor was rated at 35 mbar range and -55°C to +125°C operating temperature. The accuracy requirement on the sensor was 0.01% full scale and flowed down to an equivalent requirement of < 0.01 mbar of package induced error in the sensor. Beyond this error, package effects would destroy measurement accuracy in addition to underutilizing sensor capability. Six sigma studies and experiments on an optimized package design suggested that repeatability effects cannot be measured to statistical significance by any known external method such as optical interferometry, thus suggesting that a MEMS sensor is possibly the best and only method of evaluating low residual strain.
Optimal Trajectory to Minimize Mechanical Vibration for Fast Positioning
Authors: Semba Tetsuo , White Matthew T.
Published: April 2008

Input shaping techniques have been proposed to reduce the vibration in the positioning of the manipulators. However, a practical application is not simple as the target requirements becomes more precise, because the number of mechanical resonances that need to be taken into account increases, and the robustness against the resonant frequency variations is more critical. The vibrations of the positioning at the final state are easily estimated by the plant transfer function and the jerk waveforms at acceleration, deceleration, and settling. The optimal control input for faster positioning can be obtained by minimizing the width of the jerk and minimizing the mode excitations at the same time. This optimization process can be performed by an adaptive filtering technique. It is based on the least-square algorithm, which generates the jerk waveform that minimizes the least-square sum of the vibration only at the settling. Effectiveness of the method is demostrated by computer simulations and the results for a hard disk drive application are also presented.
Effect of Warp on the Multiple Equilibria of a Hydrodynamically Coupled Flexible Disk
Authors: Nair Nikhit N. , Warner Grant M.
Published: April 2008

In this paper, a hydrodynamically coupled flexible disk rotating in a thin housing is mathematically modeled and an attempt is made to explain the jump instability phenomenon that occurs when the disk rotation speed is varied slightly. The disk is assumed to have an initial warped profile due to slight imperfections in the manufacturing process. After non-dimensionalization of the participating variables, a hybrid formulation is carried out. Radial flows above and below the disk are taken into consideration. The deflection and pressure equations form a coupled system, and a solution is attempted using the shooting method. The deflections obtained are plotted to obtain the deflected disk profile and appropriate conclusions are drawn.
An Adaptive Fuzzy Controller for Constant Cutting Force in End-Milling Processes
Authors: Xu Chengying , Shin Yung C.
Published: April 2008

A novel multi-level fuzzy control (MLFC) system is introduced and implemented for online force control of end-milling processes to increase machining productivity and improve workpiece quality, where the cutting force is maintained at its maximum allowable level in the presence of different variations inherent in milling processes, such as tool wear, workpiece geometry and material properties. In the controller design, the fuzzy rules are generated heuristically without any mathematical model of the milling processes. An adaptation mechanism is embedded in to tune the control parameters on-line and the resultant closed-loop system is guaranteed to be stable based on the input-output passivity analysis. In the experiment, the control algorithm is implemented using a National Instrument real-time control computer in an open architecture control environment, where high metal removal rates (MRR) are achieved and the cycle time is reduced by up to 34% over the case without any force controller, and by 22% compared with the regular fuzzy logic controller (FLC), thereby indicating its effectiveness in improving the productivity for actual machining processes.
Mechatronic System Integration for Senior Students
Authors: Kulic Dana , Croft Elizabeth
Published: April 2008

This paper describes the design and implementation of a senior level course in mechatronic system integration for students completing a mechatronics engineering option in mechanical engineering. The course is designed to give students theoretical and practical experience with a large-scale mechatronic system, and a variety of control, sensing and actuating architectures. The lecture component of the course introduces students to large-scale project integration and interface design, as well as system architecture design. Students learn about alternative control hardware platforms commonly used in industry, such as motion control hardware, field programmable gate arrays and programmable logic controllers. The selection and system integration of various industrial sensors, including vision, are presented. Students also learn about networked control and discrete event control approaches for large-scale industrial systems. The course contains a significant practical laboratory component. In a series of laboratory sessions, students develop and implement subsystems of a part sorting machine, culminating in the integration and demonstration of an automated, autonomous, sensor driven electro-mechanical system for sorting randomly delivered parts. The course offers students a theoretical background as well as significant practical experience with large scale mechatronics systems, as would be encountered in industry. This paper describes the lecture and laboratory content, and the experiences from the first offering of the course.
Residual Stress Variation in Polysilicon Thin Films
Authors: Mueller Andrew J. , White Robert D.
Published: April 2008

This paper compares the use of four mechanical methods for characterization of residual stress variation in low pressure chemical vapor deposited (LPCVD) polysilicon thin films deposited, doped, and annealed under different conditions. Stress was determined using buckling structures, vibrating microstructures, static rotating structures and the wafer curvature method. After deposition of 1.0 μm of polysilicon at 625°C and 588°C the stress in the wafers is 230 MPa compressive (stdev = 1.2 MPa) and 340 MPa compressive (stdev = 10.4 MPa), respectively. Deposition of 0.6 μm at 580°C results in a tensile stress of 66 MPa (stdev= 52 MPa). Following doping, all stresses are compressive. Boron doping of the 625°C and 588°C deposited films produces a compressive stress of 149 MPa (stdev= 28.6 MPa) and 100 MPa (stdev= 29.5 MPa). Phosphorous doping of the 588°C and 580°C deposited films produces a compressive stress of 54 MPa (stdev = 0.3 MPa) and 80 MPa (stdev= 5.3 MPa), respectively. Annealing through rapid thermal processing (RTP) at temperatures of 1000°C – 1100°C reduced the stresses by 20-50 MPa, but the stresses remained compressive. These values are measured using the wafer curvature method. Values obtained from the other microstructure methods agree with stresses determined by wafer curvature with the exception of the rotating structures which showed 20% lower stress readings.
Molecular Dynamics Simulation of Ultrafast Laser Ablation of Fused Silica
Authors: Cheng Changrui , Xu Xianfan , Wang Yaguo , Strachan Alejandro
Published: April 2008

In recent decades, ultrafast lasers have been used successfully to micro-machine fused silica. The high intensity laser pulses first excite valence electrons to the conduction band via photoionization and avalanche ionization. The excited free electrons absorb laser energy, and transfer its energy to the ions, resulting in the temperature rise. This ionization leads to significant changes in Coulomb forces among the atoms. Both thermal and non-thermal (Coulomb explosion) ablation processes have been discussed in the literature [1]. This work applies molecular dynamics technique to study the interaction between ultrafast laser pulses and fused silica and the resulting ablation. The main goal of this work is to investigate the ultrafast laser ablation process of fused silica, and to reveal the mechanisms leading to the material's removal. In this MD simulation, the equilibrium state of fused silica is first established at 300 K, and the laser heating and material removal processes are simulated. The ionization of the material and the energy coupling between the laser beam and free electrons and ions are considered. Thermal and non-thermal mechanisms of fused silica ablation are discussed based on calculation results.
Ultrafast Diagnostics of Coherent Phonon Excitation and Energy Transfer
Authors: Wu Alexander Q. , Xu Xianfan
Published: April 2008

Time resolved reflectivity of bismuth thin film evaporated on a silicon substrate is measured by an 80 femtosecond (fs) laser at a center wavelength of 800 nm. The reflectivity data reveal that coherent optical phonons (A1g) near 2.9 THz (1 THz = 1012 Hz) are excited by the 80 fs laser pulses. Analyses of the reflectivity data reveal key parameters related to electron and phonon dynamics, including phonon excitation and de-phasing and electron-phonon energy coupling. It is also found that the phonon frequency peaks are red-shifted and broadened at higher laser fluences.
Skill-Centered Syllabus for Undergraduate Mechanical Engineering Education
Authors: Rodriguez Carlos F. , Pinilla Alvaro E.
Published: April 2008

Recent changes in higher education policy in Colombia (South America) have forced educational institutions and universities to consider reducing undergraduate engineering programs from the traditional 5 or 6 years (170 credit hours) to four years (136 credit hours). This reduction is a worldwide trend, mainly due to a lack of financial resources supporting high standards of professional education. Additionally, institutions are restructuring their curricula to adjust to the broader spectrum of career development opportunities for the graduating engineer and the new challenges faced by practicing engineers. Also, engineering education in Colombia needs to adjust to Colombia's necessities as a developing country. In response to the above-mentioned circumstances, the mechanical engineering department of the Universidad de Los Andes (UdLA) has proposed a new mechanical engineering (ME) undergraduate syllabus. This paper summarizes the process undergone by the ME department of the Universidad de Los Andes to review our syllabus and propose alternative approaches. Our new ME syllabus applies a skill-centered approach structured by four priorities: 1) the primary professional role of an engineer is in project development, 2) the engineer needs an in-depth knowledge of the sciences (physics, chemistry and biology) and mathematics; 3) the engineer also needs a general education in the social sciences and arts and, 4) the engineer should master the core concepts of mechanical engineering. These four priorities agree with the US study of the Engineer of 2020. Our restructured syllabus evenly introduces these priorities early in the undergraduate ME program. Our ME Department implemented the new syllabus for first year students in January 2006. Positive results have already started to emerge. This article provides an overview of the higher education quality assurance system in Colombia and a description of the Universidad de Los Andes new ME syllabus.
An Analysis of the Loss Mechanisms in Low-Speed Axial Fans Using Scaling Arguments and Their Effects on a Proposed New Definition of Efficiency
Authors: Neal Douglas R.
Published: April 2008

Low-speed axial fans are used extensively for ventilation purposes in industrial and commercial buildings. In agricultural applications, such as a greenhouse, the ventilation is critical, since entire crops can be damaged or destroyed if a clean air supply is not maintained. The cost-marginal nature of these businesses demand that operating costs be kept to a minimum, hence there is a strong motivation to develop higher efficiency ventilation fans. An analysis of a low-speed axial fan has been developed using a control volume-based energy balance. The specific fan is an axial ventilation fan that is commonly found on agricultural facilities such as green-houses or livestock buildings. These fans induce an airflow from a large building into the open atmosphere at very low (or often effectively zero) system restriction or pressure rise. The definition for static efficiency, which is commonly used by the axial fan community, is examined and its implications are discussed. Since static efficiency yields a zero-percent efficient fan at a zero pressure rise operating condition, the ventilation fan industry has developed an alternate definition of efficiency. This alternate definition of efficiency, along with other proposed definitions, are described and their limitations are discussed. A new definition of efficiency is introduced and its basis in the integral energy equation is identified. The primary loss mechanisms of low-speed axial turbomachinery are discussed and scaling arguments are developed and used in the integral energy equation analysis. The results of this analysis yield an expanded expression of efficiency in which the loss mechanism terms can be empirically determined. When analyzed with values for a particular fan system, these results can further be used as the basis for an optimization study of that fan system.
Plasmonic-Enhanced Radiative Transfer Through Nanoscale Aperture Antennas
Authors: Jin Eric X. , Wang Liang , Xu Xianfan
Published: April 2008

Nanoscale ridge aperture antenna as a nanoscale high transmission optical device is demonstrated. High transfer efficiency and confined radiation are achieved simultaneously in the near field compared with regularly-shaped apertures. The radiation enhancement is attributed to the fundamental electromagnetic field propagating in the TE10 mode concentrated in the gap between the ridges. The transfer efficiency is further enhanced through plasmon excitation and resonance. This paper reports spectroscopic measurements of radiative transfer through bowtie shape ridge aperture antennas. Resonance in these aperture antennas and its relation with the aperture geometry are investigated. The near-field radiation through the bowtie aperture and the regular nanoaperture is also mapped with near-field scanning optical microscopy. It is revealed that plasmon excitation and resonance contribute to the radiation enhancement through the ridge aperture antennas.
Modeling and Simulations of a Two-Degree-of-Freedom SMA Actuator for Mirror Positioning
Authors: Williams Eric , Elahinia Mohammad
Published: April 2008

Shape memory alloys (SMAs) provide compact and simple actuation for a variety of systems. Automotive applications of these materials, although very attractive, have not been fully explored. This is partly due to the complex behavior of the alloys. A two degree of freedom SMA actuator has been developed to orient the position of a rear-view-mirror. This paper presents dynamic simulations of the SMA actuator. The strong interdependence of the thermomechanical behavior of the alloy and the dynamics are considered to greater improve the accuracy of the true system. The modeling of the nonlinear friction behavior is also of great importance to the general dynamics of the actuator and eventually the control system.
Coupled Thermal-Stress Analysis for FC-BGA Packaging Reliability Design
Authors: Hirohata Kenji , Hisano Katsumi , Kawakami Takashi , Aoki Hideo , Takubo Chiaki , Takahashi Kuniaki , Pecht Michael G.
Published: April 2008

In order to improve electronics packaging design, it is important to evaluate cooling performance and reliability of the electronics packaging structure. To that end, it is necessary to predict the temperature, deformation, and stress distribution of the package under field conditions. In the case of a packaging structure comprising a flip-chip ball grid array (FC-BGA) package, a heat spreader, thermal grease, a cooling structure, solder joints, and a motherboard, an increase in the contact thermal resistance may occur, depending on the interface contact condition between the cooling structure and the heat-spreader due to the thermal deformation of the package. Contact thermal resistance problems involve the interactive relationship of the thermal and stress distribution. A coupled thermal-stress analysis, with consideration of the time-space variation of contact thermal resistance, was conducted to duplicate the behavior of temperature, deformation, and stress distributions of a FC-BGA package under field conditions. It was found (1) that the average contact thermal resistance across the interface between the heat-spreader and the plate fin, which was predicted by the coupled thermal-stress analysis, increased compared to that in the case of uniform contact pressure, and (2) that the contact thermal resistance will vary depending on the deformation mode, such as convex upward and downward, due to heat dissipation during field conditions. In addition, a reliability prediction method for thermal fatigue failure of solder bumps based on coupled thermal-stress analysis and statistical and probabilistic methods was proposed in order to select a suitable packaging solution at an early stage of design.
An Experimental Study of Transitional Behavior in Physiological Flow Regimes
Authors: Sturgeon Victoria , Savas O¨mer , Saloner David
Published: April 2008

An experimental study is made of flow through models simulating the human abdominal aorta and human coronary arteries. Compliant silicone models are used to investigate fluid-wall interactions of geometries simulating arteries in healthy and diseased states, with the difference between the two being a localized wall thickening on the diseased model to simulate plaque deposition. Physiological flow waveforms and constant pressure external to the model wall are used as input conditions. Using flow visualization and particle image velocimetry, flow stability and transitional behaviors are studied and compared with velocity profiles for resting and exercise states deduced from clinical flow rate data. In these Reynolds and Sexl-Womersley matched experiments, the flow phantom representing the diseased slate demonstrates recirculation zones both upstream and downstream of the stenosis, while the healthy artery demonstrates a more unidirectional flow pattern. The contrast between the high-Reynolds, high-Sexl-Womersley number flow regime of the abdominal aorta and the lower-Reynolds, lower-Sexl-Womersley number behavior of the coronary arteries illustrates the importance of transitional behaviors in the human body and specifically in the progression of atherosclerosis.
Rheo-Dielectric Study in Polymeric Nano-Suspensions
Authors: Peng Yiyan , Prochniak David J. , Shkel Yuri M.
Published: April 2008

Dielectrostriction is variation of dielectric properties of material with deformation. Linear relation between stresses and dielectric response, called stress-dielectric rule, closely resembles stress-optical rule. In addition, microscopic model predicts that dielectrostriction measurements are very effective for studying microstructure and size distribution of the suspended inclusions. In this paper, dielectrostriction effect is probed in silicone/aluminum oxide (Al2O3) suspensions having various distributions of micro- and nano-particles. A rosette of two planar capacitor sensors with mutually perpendicular electrodes is employed to detect the dielectrostriction responses and measure the strain-dielectric coefficients of suspensions during oscillatory shear flow. Experimental results confirm stress-dielectric rule for all suspensions; and show dielectrostriction response sensitive to particle distribution.
Teaching the Fundamentals of Thermodynamics and Fluid Mechanics Through an Integrated Systems Approach
Authors: Boettner Daisie D. , Norberg Seth A. , Melnyk Richard V. , Highley Justin L. , Rounds Michael J. , Arnas A. O¨zer
Published: April 2008

The mechanical engineering faculty at the United States Military Academy recently implemented an integrated, two-course thermal-fluid systems sequence that presents fundamental thermodynamics and fluid mechanics topics. Instructors introduce students to these topics by exploring operational aspects of five complex systems: a helicopter, a power plant, a total air-conditioning system, an automotive system, and a high performance aircraft. Additionally, both courses incorporate laboratories, demonstrations and hands-on educational aids, design projects, and self-learning opportunities to reinforce understanding of fundamental concepts. Results from the first year the sequence was taught indicate students prefer learning topics from a global perspective and integrating thermodynamics and fluid mechanics topics reinforces student learning and retention of fundamental concepts. Challenges to teaching an integrated thermal-fluid systems sequence include lack of availability of textbooks that present thermodynamics and fluid mechanics topics in a truly integrated manner and establishing equivalency of courses within the integrated sequence with courses taught at other universities for those students on semester exchange programs.
A Method of BGA Bump and Solder Joint Design for Optimal Solderability
Authors: Wu Xiaohua , Huang Jay , Qian Zhengfang
Published: April 2008

This paper provides a method and algorithm for fast design of BGA bump/solder joints, quick analysis of solder defect root cause and design improvement in a cost saving manner. The method uses a general and explicit form to incorporate the cause and effect relationship of design and process parameters into BGA solder interconnect designs, provides a design for reducing or eliminating voids in BGA solder joints. The design method for BGA bump, dummy bump, solder interconnect and pad stack designs enables rapid design evaluation for BGA solderability. Typically, it provides 1) fast design for BGA bump and solder joint with respect to high solderability; and 2) a quantitative guideline on how to improve BGA designs for an optimal solderability.
Interactive Soft Tissue Deformation Simulation Using Physically Based Modeling
Authors: Chi Xiaoyi , Leu Ming C.
Published: April 2008

This paper presents a study on physically based modeling and simulation of soft tissue deformation, with the goal of producing realistic, real-time effects during the simulation. We consider soft tissue deformation as a solid mechanics problem with a linear elastic constitutive law. A point collocation based meshfree method is employed to solve the governing equations. To achieve real-time performance, an octree data structure is used to organize the support sets and the nodes to expedite the computation in the meshfree method. The developed system brings together the surface representation for visualization and meshfree modeling for physically based animation to set up a virtual reality environment for soft tissue surgery simulation.
Non-Rotational-Loosening Behavior of Bolted Joint Constructed From Steel Tube and Plates
Authors: Fujioka Yasuo , Hara Koichi , Sawa Toshiyuki
Published: April 2008

The reduction in axial tension was investigated in bolted joints, which comprise two hot-rolled steel plates and a carbon steel tube sandwiched between the plates. After tightening the bolts, vibration tests were carried in the following two cases. In the first case, flat-faced steel tubes without having any serrations on both ends of the tube were used, and the effect of wave profiles of the external load was investigated. These wave profiles are those of random waves, quasi-random waves that are obtained by only eliminating random waves with small amplitudes, and 7-step programmed waves generated from random waves. In each test, the maximum and the minimum amplitudes are the same. In the other case, the effect of the convex height of the serrations, which are cut on the end face of a tube, was investigated. In addition to the flat faces, the end faces of the tubes were serrated with three different heights for the purpose of comparison. In this case, the vibrations were applied only by means of sinusoidal waves. The effect of the wave profile on the external load is as follows. During the period of low cyclic loading, the bolt axial tension was reduced in the following order: the reduction was the minimum for the 7-step programmed waves, followed by the quasi-random waves, and was maximum for the random waves. As the number of cycles increases, the scattering range of bolt axial tensions corresponding to three types of waves becomes smaller. Furthermore, a comparison of this result with a fatigue test on mild steels indicates that the vibrating wave affects the reduction in axial tension, this is evident from the wave profiles and frequency. With regard to the convex height of the serration, after 106 cycles, the data shows that the lower the convex height, smaller is the reduction in the axial tension. The value of relative micro-slippage of the contact surfaces between the carbon steel tube and the steel plates is small at the sharp serrations. Therefore, the reduction in the axial tension is assumed to be mainly due to the cumulative effect of the plastic deformations.
A Single Phase Anti-Swing Fuzzy Logic Controller for an Overhead Crane With Hoisting
Authors: Trabia Mohamed B. , Renno Jamil M. , Moustafa Kamal A. F.
Published: April 2008

This paper presents a novel approach for automatically creating anti-swing fuzzy logic controllers for overhead cranes with hoisting. This approach uses the inverse dynamics of the overhead crane to determine the ranges of the variables of the controllers. The control action is distributed among three fuzzy logic controllers (FLCs): travel controller, hoist controller, and anti-swing controller. Simulation examples show that the proposed controller can successfully drive overhead cranes under various operating conditions.
Modal Interactions in Resonant Microscanners
Authors: Daqaq Mohammed F. , Abdel-Rahman Elihab M. , Nayfeh Ali H.
Published: April 2008

The fast response of micromirrors and their ability to achieve large scanning angles and low wavelength sensitivity, has made them an appealing substitute for traditional scanning and display technologies. To achieve large rotation angles, while minimizing the voltage requirements, the microscanner is excited at its resonance frequency and then used to steer a light beam along a surface. In this work, we develop a comprehensive model of a torsional microscanner. Based on the eigenvalue problem, we reduce the model to a 2-DOF lumped-mass model that captures the significant dynamics of the microscanner. We use the method of multiple scales to derive an approximate analytical solution of the microscanner response to combined DC and resonant AC voltage excitation. We examined the characteristics of the solution and found that, for a range of DC voltage, a two-to-one internal resonance occurs between the first two modes. Therefore, the energy fed to the first (torsional) mode may be channeled to the second (bending) mode causing an undesirable steady-state response. This phenomenon results in significant degradation in the microscanner performance, therefore, the designer needs to identify it, design around it, or control it.
Polarization Swiching in (111) Oriented PZT Thin Films
Authors: Oates William S. , Gruverman Alexei
Published: April 2008

Local domain structures in Pb(Zr,Ti)O3 (PZT) ferroelectric thin films have been investigated using linear finite element analysis to qualitatively assess the effect of crystal structure, domain wall orientation and mechanical constraints from electrodes on local polarization switching behavior. The finite element model was used to illustrate that the evolution of residual stress during polarization reorientation may play an important role in the backswitching behavior which has been observed experimentally in (111)-orientated PZT films. The domain size and orientation used in the finite element model utilizes domain sizes determined from piezoresponse force microscopy (PFM) measurements given in the literature together with domain wall orientation from strain and charge compatibility in the (111) orientation. During polarization switching, domains with polarization components aligned anti-parallel to the applied field are expected to switch 90° to partially align with the applied field. 180° switching is not expected to occur in the (111) oriented film. The 90° switching induces residual stress that is computed using the finite element model. It is illustrated that thicker top electrodes increase the residual stress in the ferroelectric layer which may play an important role in polarization retention behavior in ferroelectric capacitors.
Thermal Expansion and Isotopic Composition Effects on Lattice Thermal Conductivities of Crystalline Silicon
Authors: Chen Yunfei , Wang Guodong , Li Deyu , Lukes Jennifer R.
Published: April 2008

Equilibrium molecular dynamics simulation is used to calculate lattice thermal conductivities of crystal silicon in the temperature range from 400K to 1600K. Simulation results confirmed that thermal expansion, which resulted in the increase of the lattice parameter, caused the decrease of the lattice thermal conductivity. The simulated results proved that thermal expansion imposed another type resistance on phonon transport in crystal materials. Isotopic and vacancy effects on lattice thermal conductivity are also investigated and compared with the prediction from the modified Debye Callaway model. It is demonstrated in the MD simulation results that the isotopic effect on lattice thermal conductivity is little in the temperature range from 400K to 1600K for isotopic concentration below 1%, which implies the isotopic scattering on phonon due to mass difference can be neglected over the room temperature. The remove of atoms from the crystal matrix caused mass difference and elastic strain between the void and the neighbor atoms, which resulted in vacancy scattering on phonons. Simulation results demonstrated this mechanism is stronger than that caused by isotopic scattering on phonons due to mass difference. A good agreement is obtained between the MD simulation results of silicon crystal with vacancy defects and the data predicted from the modified Debye Callaway model. This conclusion is helpful to demonstrate the validity of Klemens' Rayleigh model for impurity scattering on phonons.
Transport From a Volatile Meniscus in a Microtube
Authors: Wang Hao , Murthy Jayathi Y. , Garimella Suresh V.
Published: April 2008

Transport at the meniscus of a volatile liquid evaporating inside a microtube is numerically investigated. Evaporation at the meniscus is coupled with the vapor diffusion into the ambient. The evaporation is found to be stronger at the corner of the meniscus than at its center, which creates a temperature gradient resulting in thermocapillary or Marangoni flow along the meniscus. The existence of either gravity or mild imposed temperature gradients results in asymmetric flow structures. For a meniscus in a horizontal microtube, a large vortex near the meniscus covers much of the diametric cross-section of the tube, with a small vortex present above. The simulations are consistent with experimental measurements.
A Combined Method for the Investigation of Coupled Bandpass-Lowpass Nonlinear Oscillators Based on Hilbert Transform and Perturbation Analysis
Authors: Xiros Nikolaos I. , Georgiou Ioannis T.
Published: April 2008

The nonlinear coupling dynamics between a bandpass and a lowpass subsystem is investigated by partitioning the system state vector to a lowpass and a bandpass part. The corresponding dynamic equations of the lowpass part are formed on the assumption of linearity when unforced. Its excitation includes an external disturbance vector and a nonlinear static term, standing for the coupling of the lowpass dynamics to the bandpass part of the full system. For the bandpass part, the constant matrices appearing in the conventional form of the state-space representation of linear time invariant systems are substituted by matrix functions depending upon the state vector of the lowpass subsystem. A convenient method for describing this interaction between spectrally separated subsystems, which can be established only if their coupling is nonlinear, is the Hilbert transform. The methodology proposed is applied to a typical electromechanical oscillator, where it is compared against the standard perturbation analysis results.
Model-Based Torque Control of Piezoelectric Ultrasonic Motors
Authors: Dabney James B. , Harman Thomas L. , Ghorbel Fathi H. , Chakkungal Joseph J.
Published: April 2008

Traveling wave piezoelectric ultrasonic motors (PUMs) are ideal actuators for a variety of important applications including medical and space robotics, haptic interfaces, and positioning devices. Consisting of a single moving part, the motors are much simpler mechanically than other drive systems that require transmissions and brakes. Many potential PUM applications require accurate real-time control of output torque, which is difficult due to the highly nonlinear PUM dynamics. This paper presents an algorithm that adjusts PUM drive signal frequency to achieve output torque control throughout the speed range of a typical commercial PUM.
Modeling and Control of High Speed Mechanisms Using Inverse Dynamic Analysis
Authors: Li Yanzhi , Sahinkaya M. Necip
Published: April 2008

Inverse dynamic analysis can be used in designing controllers, but the computational requirements may prevent its use in real time. A combined piecewise linearization and off-line inverse dynamic analysis approach has been exploited in this paper to achieve the required computational efficiency with the convenience of traditional linear controllers, coupled with the accuracy and adaptability of inverse dynamic analysis. The paper simulates a three-degree-of-freedom RRR planar mechanism to demonstrate the techniques. An inverse dynamic analysis of this mechanism is carried out for different desired motions and for different operating speeds. A piecewise linearization approach is introduced to represent the system as a multi-input multi-output linear system with motion and speed dependent coefficients. A separate linearization method is developed to determine the error dynamics off-line. A standard linear-quadratic regulator is applied to the linearized model for the design of a feedback controller. The robustness against external disturbances of the proposed adaptive linearized feed-forward and feedback controller is examined by simulated examples. Most of the computationally demanding inverse dynamic and linearization calculations are carried out off-line, therefore the technique offers many potential applications involving highly complex systems.