bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Magnetic Property Characterization of PY/CO Multilayer Films
Authors: David Priya , Meletis E. I.
Published: April 2008

Multilayered films have emerged as an attractive choice of coating material in magnetic recording media and magneto-resistance device related applications. These films possess advantages such as excellent magnetic properties, good corrosion resistance and high chemical stability. Hence, it is imperative that their structural and magnetic properties be characterized so that they can be tailored for specific applications. The present study aims towards the development and characterization of Platinum (Pt)/Cobalt (Co) multilayer films for magnetic and structural properties. Pt/Co multilayered films were deposited on Silicon (Si) substrate using dual electron beam co-evaporation. Four layers of each Pt and Co were deposited on a Si substrate, forming a multilayer film. Controlled deposition rates were used in order to attain the desired thickness of Co and Pt layers. The films were characterized using scanning and transmission electron microscopy and surface profilometry. Magnetic property measurements were conducted on these films in both perpendicular and parallel orientations, in order to understand the correlation between structure of various constituent elements of the film and their magnetic behavior. Results are analyzed and compared with those obtained from previous studies on similar multilayer films, to gain a better understanding of the effect of various parameters on properties of the film.
Development of a Control-Oriented Model for Simulation of SOFC-Based Energy Systems
Authors: Sorrentino Marco , Guezennec Yann G. , Pianese Cesare , Rizzoni Giorgio
Published: April 2008

This paper deals with the development of a control-oriented model for simulation of planar solid oxide fuel cells (SOFCs). A hierarchical modeling structure has been set-up to identify a simplified model that allows describing the dynamic behavior of an SOFC with satisfactory accuracy, affordable computational burden and limited amount of experimental data. Particularly in this work, a steady-state relationship that links cell voltage to current density and temperature has been inferred from a phenomenological 1-D model previously developed by the authors. Then, a first order model has been obtained by applying the conservation of energy principle (heat balance) to a lumped control volume that includes air and fuel channels, interconnect and solid tri-layer (i.e., electrolyte and electrodes). A state-space representation of the model also is presented, having the cell outlet temperature and the cell voltage as state and output variables, respectively. Model validation has been conducted by comparing the cell response to load (i.e., current density) variations with data generated by means of a physical comprehensive model previously published by Achenbach. Extensive simulation of the cell dynamic behavior has been performed in order to analyze the main system dynamics with respect to changes in cell temperature, load, excess air and fuel utilization. The results of this analysis will serve as a tool for both optimal design and sizing, as well as for the energy management of hybridized (i.e. supported by batteries or supercap) SOFC-based power generation systems.
Assembly at the Nanoscale: Heterojunctions of Carbon Nanotubes and Nanocrystals (Keynote)
Authors: Ozkan Cengiz S.
Published: April 2008

This paper reports the controlled synthesis of multi-walled Carbon Nanotube-Quantum Dot (CNT-QD) heterojunctions using the Ethylene Carbodiimide Coupling procedure (EDC). Thiol stabilized ZnS capped CdSe quantum dots containing amine terminal groups (QD-NH2) were conjugated with acid treated Multi-Walled Carbon Nanotubes (MWCNT) ranging from 400 nm to 4μm in length. SEM, TEM, EDS and FTIR were used to characterize the conjugation process.
Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel
Authors: Mukherjee Abhijit , Kandlikar Satish G.
Published: April 2008

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.
Filters Parametrized by Orthonormal Basis Functions for Active Noise Control
Authors: Zeng Jie , de Callafon Raymond
Published: April 2008

Parametrization of filters on the basis of orthonormal basis functions have been widely used in system identification and adaptive signal processing. The main advantage of using orthonormal basis functions for a filter parametrization lies in the possibility of incorporating prior knowledge of the system dynamics into the identification process and adaptive signal process. As a result, a more accurate and simplified filter with less parameters can be obtained. In this paper, several construction methods of orthonormal basis function are discussed and analyzed. An application of active noise control based on these orthonormal basis constructions is presented.
The Effects of Processing on the Topology and Mechanical Properties of Negative Poisson’s Ratio Foams
Authors: Alderson Andrew , Alderson Kim L. , Davies Philip J. , Smart Gillian M.
Published: April 2008

Combined heat treatment and applied mechanical strains have been employed to modify the structure and properties of polyurethane (PU) foams. Consequently, foams with a range of pore sizes, shapes and orientations have been produced, including those possessing auxetic (negative Poisson’s ratio) behaviour. Four conversion conditions were employed: triaxial, biaxial and uniaxial compression (to linear compression ratios of 0.9, 0.8 and 0.7) and uniaxial tension to (linear extension ratios of 1.1 and 1.2). The converted foams were then observed by either SEM or optical microscopy, as appropriate, to determine the pore structure. Mechanical properties were measured using tensile testing in conjunction with videoextensometry, allowing the values of Young’s modulus and Poisson’s ratio to be ascertained. Increased anisotropy in the pore structure and elastic properties was observed. The biaxial as well as the triaxial conversion routes led to auxetic behaviour for the PU foams.
Large Eddy Simulation of a Three Dimensional Buoyant Jet
Authors: Satish M. , Ma F. , Islam M. R.
Published: April 2008

This study is related to the numerical simulations of a three dimensional buoyant jet. The governing equations of the fluid are solved with the help of a buoyancy-extended large eddy simulation (LES) numerical model. In addition, the dynamic procedure is used to evaluate the Smagorinsky model coefficient. The finite difference formulations of the governing equations are split into three parts related to advection, dispersion and propagation. The advection part is solved by the QUICKEST scheme. The dispersion part is solved by the central difference method and the propagation part is solved implicitly by using the Gauss-Seidel iteration method. The initial turbulence of the buoyant jet from the orifice is accounted for by introducing random disturbances to the flowing parameters. Ensemble averaged relationships for the buoyant jet trajectory; jet sizes and concentration dilution are presented. The salient characteristics of the buoyant jet are captured, including variability among different realizations of the buoyant jet, the development of protuberances, the horseshoe cross sectional shape and the hollow trough along the upper surface of the jet. The protuberance characteristic and the asymmetric shape of the jet from the present study are compared with the results from the conventional κ-ε model. The horseshoe cross sectional shape and the trough or bifurcation characteristics are investigated by studying the inner structures of the flow field. These quantitative relationships and qualitative observations are found to be in good agreement with experimental results from an earlier investigation.
Intelligent Dynamic Production Scheduling in High-Mix Low-Volume Manufacturing Systems Under Uncertain Environment
Authors: Ali Sk Ahad , Seifoddini Hamid , Sun Hong
Published: April 2008

Today’s globalization market drives industries toward increased expectations on lean production. These expectations have put industries under pressure to become more agile under highly dynamic market and manufacturing conditions in the high-mix low-volume manufacturing systems. Dynamic production scheduling is a key factor in fulfilling the customer’s expectation. It becomes more critical due to dynamics and uncertainty in the manufacturing systems. This research addresses the uncertainty consideration of machine and labor for dynamic production scheduling. Fuzzy based system is used to capture the labor and machine uncertainty and implemented in simulation environment. Based on the variability from the simulation environment, a genetic algorithm based optimization tool is developed for dynamic production scheduling. The proposed method is validated with real-world applications.
Enhancement of Fracture Toughness of Syntactic Foams by Rubber Addition
Authors: Wahab M. A. , Gorugantu V. B. , Gupta Nikhil
Published: April 2008

Microballoons (hollow-particles) filled polymeric composites, known as “Syntactic Foams” find extensive applications in aerospace structures, which demand careful study and testing before they can be used effectively in service conditions. Hybrid syntactic foams have been fabricated in this study with rubber reinforcements (2% rubber and 63% microballoons) and characterized for the fracture behavior. The three-point bend test results show that syntactic foams with rubber reinforcements had higher density and fracture toughness than syntactic foams without inclusion of rubber reinforcements. The load displacement curves showed a small plastic deformation region prior to the specimen fracture. Extensive scanning electron microscopy was carried out to understand the origin of the fracture toughness properties and related them to the material microstructure.
Thermal Performance Prediction for High Power Processors at High Altitude
Authors: Xu Guoping
Published: April 2008

A method to predict high power processor thermal performance in air-cooled electronic systems at high altitude is proposed in this paper. This method employs non-dimensional heat transfer and fluid flow parameters to evaluate the impact of high altitude conditions based on measurement data at sea level. Experimental data including fan/fan tray curve, system air flow impedance and processor heat sink performance for various air flow rates at sea level are required for the analysis. Altitude correction factors will be derived from nondimensional correlations. By using these altitude correction factors, the dimensional fan curve, system air flow impedance curve, and thermal performance curve may all be transformed from sea-level to high altitude. The proposed method can be applied to thermal performance predictions of forced convection electronic components with or without air-cooled heat sinks. The method can be used in a system with any flow regime: laminar, turbulent or a combination of both. This method will be demonstrated through an example of a high end server system.
Failure Site Transition During Drop Testing of Printed Wiring Assemblies
Authors: Varghese Joseph , Song Bo , Azarian Michael H. , Dasgupta Abhijit , Pecht Michael
Published: April 2008

This paper reports on the effect of printed wiring assembly (PWA) flexural strain and strain rate and aging on the durability and failure site of Sn-Pb solders in area array packages. Two different plastic ball grid array (PBGA) package styles, one with a single die and the other with stacked die, are used for this study. We consider the effect of intermetallic growth on the failure site transition in the interconnects. Results are compared to similar studies in literature. This study quantifies durability in terms of the local PWA response (PWA flexural strain, PWA flexural strain rate, cyclic history) instead of the conventional approaches that typically use loading parameters (total impact energy, orientation and number of drops. This makes the results more generic and easier to extrapolate to different assemblies and different loading/orientation conditions. Four point bend tests are conducted on the PWAs assembled with PBGA components. A high speed data acquisition system with in-situ resistance monitoring is used to track the PWA response and the number of cycles to failure. The strain rate is varied over three orders of magnitude while the peak strain is studied over the range of 25 to 75% of the overstress limit. The durability of the specimens decreases with increasing PWA flexural strain and varies non-monotonically with flexural strain rate. As-reflowed samples (with a thin intermetallic layer), undergo a transition in the failure site from bulk solder to FR-4 board and copper trace with increasing PWA flexure. Aged samples (with a thick intermetallic layer), have lower durability and fail in the intermetallic layer for all values of PWA strain. This study identifies the PWA flexural strain and strain rate limits for failure site transition in aged and as-reflowed samples of a PBGA package.
Modeling of Transient Flow inside a Fiber Tow During Liquid Composite Molding
Authors: Yamaleev N. K. , Mohan R. V.
Published: April 2008

In liquid composite molding processes, the macroscopic flow in fiber preforms is simultaneously accompanied by the micro-scale impregnation of fiber tows. Because the interstitial space within an individual fiber tow is much smaller than the space between tows themselves, the macroscopic flow front is able to reach the downstream side of the tow before gas entrapped inside the tow can be forced out by the resin impregnation process. In this work, a quasi-2-D model for the dynamic flow behavior inside a fiber tow completely surrounded by a macroscopic resin flow is developed. In contrast to the existing models, the new model accounts for not only the surface tension effects that could influence the flow behavior at this length scale, but also the multidimensional effects and the vapor-liquid phase transition of the entrapped gas, which occurs in resin systems used in liquid composite molding. This model simulates the transient dynamics of the multi-component gas mixture entrapped inside the tow on the time scale associated with infiltrating the intra-tow region. One of the advantages of the new model is its ability to account for the delayed impregnation inside fiber tows, which eliminates the ambiguity in determining the intra-tow infiltration time of the “sink” volume, which is a required parameter for some previously developed models. The model also quantitatively predicts the time-dependent behavior of the sink term, which is needed to accurately simulate the macroscopic resin flow in the preform. The model development and analysis of the transient intra-tow flow behavior under various thermodynamic conditions are presented, and the relevance of the numerical results to the micro-void formation in liquid composite molding processes is discussed.
Sama’s Rules on Exergy
Authors: Sama Dominick A.
Published: April 2008

Each of the following topics is analyzed and discussed from a logical/philosophical viewpoint to arrive at an appropriate conclusion. • Nomenclature for Exergy. • The Proper Thermodynamic Reference Temperature for Exergy Calculations. • Exergy Calculations for Apparently Adiabatic Processes. • Exergy Destruction. • Exergy Balances. • Fuel-Use Factors for Different Forms of Exergy. • Thermodynamic Inefficiencies Not Detected by Exergy Analysis. The conclusions result in a set of governing “rules” that differ in many respects from views commonly held. Accordingly, they will be controversial. Thus, although it is not expected that these rules will be universally accepted, it is hoped that, at the least, they will stimulate further discussions within the Second Law community.
Experimental Investigations on the Prototypic Steam Explosion
Authors: Song J. H. , Kim J. H. , Min B. T. , Hong S. W.
Published: April 2008

This paper discusses results of a series of steam experiments using a prototypic material representing the molten core of nuclear power plant. Five experiments are discussed in detail in addition to a brief review of the previous experiments, where the focuses were on the effect of corium composition and external trigger on the strength of the steam explosion. A mixture of UO2:ZrO2 is used for the experiment, where the weight percent of each component is changed. One experiment was performed with corium at a composition of 70:30 without an external trigger as a reference case. Three tests were performed by using corium at the same composition with an external trigger. The last experiment was performed using corium at a composition of 80:20 with an external trigger. Various parameters are measured including the dynamic pressures on the wall of the test section and the dynamic force at the bottom of the test section. From the experimental data, the strength of the steam explosion was evaluated. It is shown that the strength of the steam explosion highly depends on the composition. A comparison between the cases with an external trigger and the cases without external trigger indicates that there is no substantial escalation of the strength of the explosion due to an external trigger.
Study of Pressure Drop of Refrigerant Mixtures During Boiling Inside Enhanced Surface Tubing Under Magnetic Field
Authors: Sami S. M. , Comeau J.
Published: April 2008

Two phase flow pressure drop characteristics observed under magnetic field during boiling of refrigerant mixtures R-404A, and R407C as well as R-507 are presented in this paper. Experiments showed that magnetic field has insignificant effect on the pressure drop. It was evident from the boiling data that the magnetic field has insignificant impact on the pressure drop. Boiling data showed was found to be correlated with a mean deviation between of ±20%.
Numerical Simulation of Fluid Flow and Heat Transfer in the Micro-Nozzle
Authors: Li Longjian , Zhang Yihua , Cui Wenzhi , Jen Tien-Chien , Chen Qinghua , Liao Quan
Published: April 2008

Micro-nozzle, based on the MEMS technology, has played an important role in orbit positioning, attitude adjusting and other applications of micro-satellites. The continuous no-slip model of two-dimensional compressible laminar flow in the micro-nozzle was proposed and solved numerically by finite control volume method. The flow and heat transfer in the micro-nozzle were computed under different conditions, including different inlet pressures, different inlet temperatures and different divergent angles. Flow field and effects of these conditions on the propulsion performance were analyzed. Finally, simulated solutions were compared and validated with the experimental results.
A Heat Transfer Correlation of Flow Boiling In Micro-Finned Helically Coiled Tube
Authors: Cui Wenzhi , Li Longjian , Xin Mingdao , Jen Tien-Chien , Chen Qinghua , Liao Quan
Published: April 2008

In the research of intube flow boiling, a widely accepted factor is that there are two main mechanisms participating in the heat transfer. One is nucleate boiling, which is dependent on the presence of active nuclei on the heated wall and the heat transfer coefficient is much influenced by the heat flux, much similar to pool boiling. In the other heat transfer mode, the boiling nuclei are fully suppressed and heat is transferred by the liquid evaporation through the interface of liquid film and vapor core. This is also called forced convective evaporation or convective boiling. In the evaporation region, the dependence of heat transfer on heat flux is not distinct and governed mainly by the mass flux and vapor quality. In the open literature on convective boiling heat transfer of refrigerant researches have been extensively conducted in straight tube. The studies, however, on two-phase flow boiling heat transfer in helically coiled tube are far less than that in straight tube. Because of the high efficiency in heat transfer and compactness in volume, helically coiled tubes are used extensively in practical industries. Therefore, it is important for application to obtain the correlations of flow boiling heat transfer coefficient in helically coiled tube. A new kind of micro-finned helically coiled tube was developed by the present authors and the flow boiling heat transfer characteristics are experimental studied in this paper, using R134a, an environment-friendly refrigerant as experimental fluid. By introducing convective boiling number NCB, as suggested by V. V. Klimenko (in Ref. [8]), the transition boundary between nucleate boiling and forced convective boiling in helically coiled tube is examined, which is much different with that in straight tube. Based on the analysis of the mechanisms of flow boiling, heat transfer correlation of the specific micro-finned helically coiled tubes is obtained, which has a mean absolute deviation of 13.8%.
Coherent Thermal Emission From Modified Periodic Multilayer Structures
Authors: Lee B. J. , Zhang Z. M.
Published: April 2008

Enhancement of thermal emission and control of its direction are important for applications in optoelectronics and energy conversion. A number of structures have been proposed as coherent emission sources, which exhibit a large emissivity peak within a narrow wavelength band and at well-defined directions. A commonly used structure is gratings, in which the excited surface polaritons or surface waves are coupled with propagating waves in air to produce coherent emission for p polarization. One-dimensional photonic crystals can also support surface waves but have not been applied as coherent emission sources. The present study demonstrates that coherent emission can be achieved by the use of a multilayer structure consisting of periodic layers (i.e., photonic crystal) coated with a polar material such as SiC. By excitation of surface waves at the interface between SiC and the photonic crystal, coherent emission is predicted for both p and s polarization. In addition to the excitation of surface waves, the emission from the proposed structure can be largely enhanced by the cavity resonance mode, which is very similar to that of Fabry-Perot etalon, as well as by the Brewster mode that occurs only for p polarization.
Probabilistic Analysis and Design of a MEMS Re-Entry Switch
Authors: Field R. V. , Reese S.
Published: April 2008

The probabilistic analysis and design of a MEMS switch during atmospheric re-entry is discussed. The switch is modeled as a classical vibro-impact system: a single degree-of-freedom oscillator subject to impact with a single rigid barrier. The excitation is assumed stationary, Gaussian, with prescribed PSD to represent the re-entry environment. A subset of the model parameters are described as random variables to represent the significant unit-to-unit variability observed during fabrication and testing of the device. The metric of performance is the amount of time the switch remains closed during the re-entry event.
Nanosphere-Assisted Direct-Patterning of Silicon Carbide by a Nanosecond Pulsed Laser
Authors: Battula Arvind , Theppakuttai Senthil , Chen Shanchen
Published: April 2008

A strategy wherein the optical near-field enhancement between the spheres and substrate obtained by irradiating with laser beam is used for nano-patterning the hard-to-machine bulk silicon carbide (SiC). For this study a monolayer of silica (SiO2) spheres of 1.76 μm and 640 nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of wavelength 355 nm and 532 nm. Scanning electron microscope and atomic force microscope are used to characterize the features. It was found that the features obtained were having diameters around 150 to 450 nm and the depths varying from 70 to 220 nm.
Studies of a Two-Stage Cyclonic Combustion System to Simulate the Time Temperature History Found in Large Utility Boilers When Firing Solid Fuel
Authors: Abd-Rahman A. , Syred N. , Griffiths A. J. , Williams K. P.
Published: April 2008

This paper describes a work programme designed to evolve a 100kW simulator for large utility boilers, based on replicating the time temperature history of the large dry bottomed utility Boiler in a much smaller, portable unit. The rationale behind the work is the increased use of biomass/coal blends in Utility Boilers and necessity of obtaining cheaply, quickly and economically information on slagging and fouling propensities in different parts of the boiler. A further problem is that many materials being considered for use as co-firing fuels have site specific licenses for use, and hence can only be utilized on that site, thus requiring site tests. The evolved solution comprises a two stage cyclone combustion system, which because of the cyclonic flows can produce similar time temperature histories with a much smaller unit and allow the possibility of investigating slagging and fouling in critical boiler areas. The design is based on a first stage inverted cyclone combustor operated fuel rich to simulate the first stage of Low NOx burners, followed by a second stage cyclone combustor where secondary air is added to complete the combustion process. Slag and deposits are collected from a number of areas of the system and are analyzed in the laboratories of Cardiff University for a wide range of physical, morphological and chemical properties. These results are then compared to deposits and slags collected from full size Utility boilers to calibrate the system and ensure that results obtained are representative of those found industrially. The paper will discuss the development of the system and how it can be matched to different boiler systems
Double Diaphragm Forming of a Discontinuous Advanced Composite Prepreg Material: Process Development and Material Modeling
Authors: Munro Christopher , Walczyk Daniel , Dvorak George
Published: April 2008

Due to their superior strength-to-weight ratios, advanced composite parts are increasingly being used by the aircraft industry. This industry is constantly looking for less costly, faster, and more reliable methods to produce advanced composite parts, while still maintaining the very high safety and reliability standards required. This paper describes a new SBCF (Stretch Broken Carbon Fiber) material being developed by Hexcel Corporation for use in forming of aerospace parts. The SBCF material is a discontinuous aligned fiber prepreg material that comes in unidirectional and woven forms. If commercialized, the SBCF material will expand the range of parts that can be formed using a double diaphragm forming (DDF) process. This paper also discusses the FEM modeling of the DDF process for the purposes of predicting part defects. Having defect prediction capabilities will reduce the time and money required to determine if a part can be formed using the SBCF material and DDF. A rudimentary orthotropic-viscoelastic model is developed for the SBCF material to be used in forming simulations being developed concurrently. Model parameters are derived from force-to-stretch (i.e. tensile tests run at a constant displacement rate) and relaxation experiments. A simple model for the diaphragm is developed and preliminary forming simulations are built. Early simulations include forming over hemi-ellipsoid and curved c-channel shapes.
University Turbine Systems Research Program: An Innovative Approach to Graduate Education
Authors: Day William H.
Published: April 2008

Under the Gas Turbine Industrial Fellowship Program, students in Bachelor’s, Master’s and Ph. D. programs studying gas turbine-related technology spend 10 to 12 weeks employed at the facilities of turbine manufacturers or users of gas turbine equipment. The program is funded by the U.S. Department of Energy. This paper describes the Fellowship program and its relationship to the DOE University Turbine Systems Research (UTSR) program.
Cost Effective Skyhook Control for Vibration Isolation Systems
Authors: Song Xubin
Published: April 2008

Traditionally a skyhook control, widely applied to vibration control, requires two sensors to measure sprung mass acceleration and relative displacement, respectively. For the implementation, these two measurement signals are converted into velocities and then the damping control signal is decided and sent to controllable HH/SS dampers. In this paper, a one sensor based skyhook control policy is developed. The proposed control policy just needs one measurement signal, sprung mass acceleration, to estimate these two velocities for semiactive control. The new strategy is explained through a typical spring-mass system of a quarter-car model. But the effectiveness of the new control approach for vibration isolation is validated with ride control through simulation study of a 7-DOF full car suspension system with application of magneto-rheological (MR) dampers.
Evaluation of Deformable Barrier Designs and Associated Compatibility Metrics in Full Frontal Impact Testing
Authors: Reagan Steven , Li Xioawei , Barbat Saeed
Published: April 2008

Several modifications to an existing deformable barrier are investigated for their ability to predict the presence of secondary energy absorbing structures (SEAS) using four deformable barrier designs with simulated impact by two vehicles. This study is motivated by the assumption that SEAS may enhance vehicle-to-vehicle compatibility and it is desirable to know if SEAS presence and its benefits are detectable through dynamic barrier testing. The considered barrier types are modifications of the Transportation Research Laboratory (TRL) barrier consisting of two layers, a front and rear. Each layer is 150mm thick with the first (front-most with respect to the vehicle) layer compression stiffness of 0.34 MPa and the second (rear-most) of 1.71 MPa. Proposed modifications to the (original, baseline) barrier are: 1. Increase the stiffness of a localized region of the front layer to 1.71 MPa (between ground heights of 330mm and 580mm). 2. Increase the depth of the second layer to 200 mm. 3. lncrease the depth of the second layer to 300 mm and use a single, non-segmented piece for the entire layer. The resulting four barrier configurations are all assumed to have 125 × 125 mm segmented “cells” supported by load time-history transducers. Computer simulation of impact by four vehicle models differing in mass and structural architecture is used. Four vehicle metrics intended to measure compatibility through impact with deformable barriers are used to quantify each barrier design’s ability to detect SEAS. Using the metrics outlined in this paper, a barrier design with stiffened rows three and four is best suited for SEAS detection. This conclusion is based on its sensitivity to four vehicle designs with and without SEAS as well as consistency of trends.
Enclosure Acoustics Modeling and Control Utilizing a FEM-BEM Approach
Authors: Whitmer Christopher E. , Kelkar Atul G.
Published: April 2008

The subject of this paper deals with developing analytical relations, computational models and active noise controller designs to help tailor of the transmission, dissipation, and the impedance of acoustic energy across an actively controlled boundary. First presented is a brief background of the theory of acoustic noise in reverberant enclosures. The boundary element formulation of the Helmholtz Integral Equation is presented, along with a finite element method (FEM) structural model. Then, an approach for coupling the models and producing a fully coupled linear control design model is presented. These developments are then specifically applied to a 3-D acoustic chamber consisting of two separate 4ft × 4ft × 8ft open ended enclosures separated by a removable actively controlled partition. The way acoustic energy interacts with an active structural boundary is then explored in greater detail using these control design models. A reduced order coupled model is then produced to investigate tailoring a controller for the desired dissipation, impedance, or transmission across boundary. LQG based controllers were investigated in this paper and an evaluation of passivity based controllers is currently underway. The resulting models and design have provided insight that will allow the design of novel structures and controllers that can be tailored for a desired acoustical transport behavior. These models and designs will be validated on an experimental test bed with the same characteristics as the chamber simulated. Future efforts will extend the FEM-BEM modeling strategy to optimize both the structural design, and the active control system to complement each other more effectively.
Controller Design and Implementation for a 6-DOF Magnetically Levitated Positioner With High-Precision
Authors: Yu Ho , Kim Won-Jong
Published: April 2008

This paper presents the controller design and implementation of a high-precision 6-degree-of-freedom (6-DOF) magnetically levitated (maglev) positioner. This high-precision positioning system consists of a novel concentrated-field magnet matrix and a triangular single-moving part that carries three 3-phase permanent-magnet linear-levitation-motor armatures. Since only a single levitated moving part, namely the platen, generates all required fine and coarse motions, this positioning system is reliable and low-cost. Three planar levitation motors based on the Lorentz-force law not only generate the vertical force to levitate the triangular platen but control the platen’s position and orientation in the horizontal plane. All 6-DOF motions are controlled by magnetic forces only. The platen is regarded a pure mass system, and the spring and damping coefficients are neglected except for the vertical directions. Single-input single-output (SISO) digital lead-lag controllers are designed and implemented on a digital signal processor (DSP). This 6-DOF fully magnetically levitated positioner has a total mass of 5.91 kg and currently exhibits a 120 mm × 120 mm travel range. This positioner is highly suitable for semiconductor-manufacturing applications such as wafer steppers. Several experimental motion profiles are presented to demonstrate the maglev stage’s capability of accurately tracking any planar and 3-D paths.
LQG Vibration Control of Aircraft Panel Using Automated State Weighting Procedure
Authors: Waite T. C. , Whitmer Christopher E. , Kelkar Atul G.
Published: April 2008

Optimal control theory has long been plagued by its inability to optimize the state and control weighting matrices specified in the LQR (Linear Quadratic Regulator) cost function. Although this control is optimal for a given set of user-defined state and control weighting matrices, the performance of the controller varies widely based on the selection of these weights. Engineers have been left with the task of choosing appropriate weighting sequences by iterating each weight until the controller performs to their satisfaction. This procedure gets increasingly more frustrating and time consuming as the size of the controller increases. The work in this paper outlines an effective strategy which reduces the engineer’s effort in finding these weights. It is shown that the introduction of an additional performance index along with the repeated perturbation of an initial guess quickly leads to a controller with excellent performance. Comparison of this automated method with a controller exhaustively designed using a standard selection method reveals a closed loop system response which has more energy reduction and more maximum amplitude reduction, all in a fraction of the time it takes to guess and check the weights. The controller will be applied to the model of an aircraft panel in an effort to reduce vibrations caused by wind. The goal is to achieve a reduction in cabin noise by controlling the vibration of such panels. The system identification procedure uses a modification of the SOCIT toolbox to achieve extremely accurate frequency domain system models. The model obtained using this method will then be used in the design and simulation of both the trial-and-error state weighted controller and the automated state weighted controller.
At-Home Systems and Controls Laboratory
Authors: Durfee William , Li Perry , Walezko David
Published: April 2008

At-home laboratories are inexpensive hardware kits that students take home and work on much like a problem set. The kits have an embedded microcontroller and communicate to the student’s home PC over a serial port. The home PC provides the needed computational horsepower for experiment control, data collection, data analysis and reporting. The microcontroller handles real-time control tasks. Two first-generation kits were developed, a fourth-order, linear mass-spring-damper system for frequency response and system identification, and an analog filtering system that uses music and synthetic sound as an input for understanding the properties of analog filters. Twenty five kits were constructed and used by students. Based on this pilot, improved, second generation kits have been designed.
The First Stokes Problem of Radiative-Convective MHD Flow in a Porous Medium
Authors: Kim Youn-Jea , Kim Young-Wan
Published: April 2008

Analytic study on the transient mixed radiative convection flow of viscous, incompressible fluids past an impulsively-started infinite vertical plate is performed. The plate is located in the transverse magnetic field embedded in a porous medium. It is assumed that the transversely applied magnetic field and the magnetic Reynolds number are very small and hence the induced magnetic field is negligible. The fluid considered here is a gray, absorbing-emitting radiation but a non-scattering medium. The Rosseland approximation is used to describe radiative heat transfer in the limit of optically thick fluids. It is also assumed here that the porous medium as an assemblage of small identical spherical particles fixed in space. The relevant transformed dimensionless governing equations are solved by using the Laplace transform technique. The obtaining results concerning velocity and temperature across the boundary layer are illustrated graphically for different values of the parameters entering into the problem under consideration. Results show that for an increase in magnetic field parameter, there is a fall in the velocity, whereas there is a rise in the velocity of the fluid for an increase in porous parameter.
Thermal Performance of Micro-Structured Evaporation Surfaces: Application to Cooling of High Flux Microelectronics
Authors: Al-Hajri E. , Ohadi M. , Dessiatoun S. V. , Qi J.
Published: April 2008

An experimental investigation on characterization of copper-finned micro-grooved surfaces for effective evaporation heat transfer with applications to cooling of high flux electronics was conducted in the present study. Performance of the copper-finned microstructures were studied as a function of operating parametric values of fin density, fin height, fin length, and channel width over a surface which was rosin soldered to a 10 mm × 10 mm heating block (typical size of an electronic chip). The performance of the copper-finned microstructures versus a flat/smooth nichrome plate in HFE-7100 was significantly higher. Two experimental conditions were investigated. In the first set of experiments pool boiling over the groves was examined, where as in the second set of experiments the fluid was forced-fed into the grooves in a forced convection mode. It is shown that the forced fed mode yields higher heat transfer coefficients than the submerged/pool boiling mode. In general the micro-grooved surfaces performed at least three times better than the flat/smooth surface and preliminary results with the forced-fed evaporation experiments suggest that an order of magnitude heat transfer coefficients are possible when compared with a smooth surface.
Three-Dimensional Simulation of Multiple-Line Laser Sintering of a Two-Component Metal Powder Layer on Top of Sintered Layers
Authors: Chen Tiebing , Zhang Yuwen
Published: April 2008

Multiple line laser scan sintering of a two-component metal powder layer on top of the sintered layers with a moving circular Gaussian laser beam is modeled numerically. The overlap between the adjacent scan lines to achieve enhanced bonding is taken into account. The binding between the newly sintered layer and existing sintered layers underneath through melting is also considered. The governing equation is formulated by a temperature-transforming model with partial shrinkage induced by melting considered. The liquid flow of the molten low melting point metal powders, which is driven by capillary and gravity forces, is formulated by Darcy’s law. The effects of the dominant processing parameters, including the moving laser beam intensity, scanning speed and number of the existing sintered layers underneath, on the shape of the heat affected zone (HAZ) are investigated. A parametric study is performed and the best combination of the processing parameters is recommended.
Quasi-Steady Axisymmetric Bingham-Plastic Model of Magnetorheological Flow Damper Behavior
Authors: Yoo Jin-Hyeong , Wereley Norman M.
Published: April 2008

A typical magnetorheological (MR) flow mode damper consists of a piston attached to a shaft that travels in a tightly fitting hydraulic cylinder. The piston motion makes fluid flow through an annular valve in the MR damper. An electro-magnet applies magnetic field to the MR fluid as it flows through the MR valve, and changes its yield stress. An MR fluid, modeled as a Bingham-plastic material, is characterized by a field dependent yield stress, and a (nearly constant) postyield plastic viscosity. Although the analysis of such an annular MR valve is well understood, a closed form solution for the damping capacity of a damper using such an MR valve has proven to be elusive. Closed form solutions for the velocity and shear stress profile across the annular gap are well known. However, the location of the plug must be computed numerically. As a result, closed form solutions for the dynamic range (ratio of field on to field off damper force) cannot be derived. Instead of this conventional theoretic procedure, an approximated closed form solution for a dampers dynamic range, damping capacity and other key performance metrics is derived. And the approximated solution is used to validate a rectangular duct simplified analysis of MR valves for small gap condition. These approximated equations are derived, and the approximation error is also provided.
Performance Characteristics of Electrocyclone With Various Inlet Shapes
Authors: Hong J.-I. , Kim Youn J. , Han J.-G. , Oh J.-K.
Published: April 2008

In this study, the performance characteristics of electro-cyclone with different inlet shapes, such as helical, tangential and involute, were experimentally investigated. The range of particle size has 0.3 to 6 μm and the inlet velocities are 10, 15, 20, and 25 m/s. Particles used in this experiment are JIS Class 11 test powder which have the density of 1.9~2.1 g/cm3 and the mass median diameter of 2.3 μm. An electrocyclone has discharge wire which was inserted in the middle of vortex-finder. The length, diameter and material of discharge wire have 20 mm, 0.6 mm and SUS304, respectively. The discharge wire was applied with a voltage of 10 kV. The collection efficiency is calculated by the particle size distribution of the upstream and downstream using a laser optical particle counter. Pressure drops were measured between two pressure taps which were located at the inlet and outlet ducts of electrocyclone using a micromanometer. For the case of the involute type, due to a minimum turbulence, the retention time of particles becomes long in electrocyclone and particles have more chances to be charged. However, the experimental results show that a helical shape has a better collection effect than the other shapes. And the pressure drop of the involute shape for a given inlet velocity is smaller than the other shapes. The collection efficiency and the pressure drop with various inlet shapes and velocity changes in electrocyclone are graphically depicted.
A Hybrid Multi-Scale Full-Spectrum k-Distribution Method for Radiative Transfer in Inhomogeneous Gas Mixtures
Authors: Wang Liangyu , Modest Michael F.
Published: April 2008

A new full-spectrum k-distribution (FSK) method has been developed, which integrates the advantage of the multi-group FSK method in dealing with temperature inhomogeneities for single-species media with the advantages of the multi-scale FSK method in dealing with partial pressure inhomogeneities for gas mixtures. The new method can achieve great accuracy for radiative heat tranfer calculations in participating media with inhomogeneities in both temperature and gas concentrations. The mathematical development of the new method is described, and several sample calculations are performed to demonstrate the accuracy the new method by comparison with line-by-line calculations.
A Proportional Hazards Neural Network for Performing Reliability Estimates and Risk Prognostics for Mobile Systems Subject to Stochastic Covariates
Authors: Lloyd George M. , Hasselman Timothy , Paez Thomas
Published: April 2008

We present a proportional hazards model (PHM) that establishes a framework suitable for performing reliability estimates and risk prognostics on complex multi-component systems which are transferred at arbitrary times among a discrete set of non-stationary stochastic environments. Such a scenario is not at all uncommon for portable and mobile systems. It is assumed that survival data, possibly interval censored, is available at several “typical” environments. This collection of empirical survival data forms the foundation upon which the basic effects of selected covariates are incorporated via the proportional hazards model. Proportional hazards models are well known in medical statistics, and can provide a variety of data-driven risk models which effectively capture the effects of the covariates. The paper describes three modifications we have found most suitable for this class of systems: development of suitable survival estimators that function well under realistic censoring scenarios, our modifications to the PHM which accommodate time-varying stochastic covariates, and implementation of said model in a non-linear network context which is itself model-free. Our baseline hazard is a parameterized reliability model developed from the empirical reliability estimates. Development of the risk score for arbitrary covariates arising from movement among different random environments is through interaction of the non-linear network and training data obtained from a Markov chain simulation based on stochastic environmental responses generated from Karhunen-Loe`ve models.