bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Analysis of Blade Geometry Generation Techniques for Centrifugal Compressors
Authors: Iancu Florin , Trevino John , Sommer Steven
Published: April 2008

It is a known fact that machined impellers result in improved compressor performance compared to cast impellers of the same design. The performance improvements can be attributed to better surface finish, more accurate geometric definition (tighter dimensional tolerances), well defined edges, and the lack of blade tip fillet on shrouded impellers. In addition, it has been observed through experimental investigations that the construction method of the impellers has an impact on performance. For flank-milled machined impellers, a hub and shroud blade profile is connected by pre-determined straight-line-elements (SLE) - which would correspond to a tool path - to generate the blade surface according to the design intent of the compressor engineer. For cast impellers, the method of connecting hub and shroud blade profile points leads to an arbitrary surface definition and is dependent upon a designer's interpretation of blade profile data and/or the solid model, as well as the CAD software. Although the shape of the hub and shroud profiles are preserved, the resulting blade surface defined by connecting these two profiles may not correspond to the design intent of the compressor engineer. Because the blade surface deviates from the design intent, the compressor performance can deteriorate. Foundries rely on a full 3D design model to create tooling for cast impellers, as opposed to hub and shroud profiles typically required of a 5-axis machining program. Therefore, these construction differences become significant for cast impellers. This paper presents computational fluid dynamic investigations of two types of impellers - with blade surfaces generated using SLE and using CAD arbitrary definitions. Because there are many different mathematical definitions that CAD tools employ for curves, the resulting arbitrary blade surface is not unique. The numerical results will help understand the causes of the performance difference as well as the effects of SLE blades to the flow through the impeller. Input conditions for computational dynamic simulations are based on experimental results. All references to experimental data in the present paper are for cast impellers. Therefore the differences in performance are attributed to blade definition (SLE vs. other) and not to differences resulting from manufacturing methods.
Fluid Mixing in Micro Scale Channel Patterned Hydrophobic/Hydrophilic Surface
Authors: Cai Qingjun , Tsai Chialun , DeNatale Jeff , Chen Chung-Lung
Published: April 2008

Micro scale fluid control or mixing is critical for chemistry and life sciences. Successful performance of on-chip biochemical analysis processes, such as DNA hybridization and PCR amplification, highly depend on rapid mixing of multiple fluid species. In this paper, a set of initial designs is developed for flow mixing. In micro channels with 100 and 200μm width, alternating regions of hydrophobic/hydrophilic surface are created on silicon surfaces by photolithography and dry etch techniques. Experimental results show that in the micro channels with 20mm length, effective mixing is observed on the device patterned by incline hydrophobic/hydrophilic grilles in which eddy diffusion mixes two liquids. In contrasts, slight mixing is caused by the development of liquid instability induced by alternating hydrophobic/hydrophilic patterns orthogonal to the flow direction.
Chaotic Behavior of Hydraulic Engine Mount
Authors: Christopherson J. , Jazar G. Nakhaie , Mahinfalah M.
Published: April 2008

The constitutive relationships of the rubber materials that act as the main spring of a hydraulic mount are nonlinear. In addition to material induced nonlinearity, further nonlinearities may be introduced by mount geometry, turbulent fluid behavior, boundary conditions, temperature, decoupler action, and hysteretic behavior. While all influence the behavior of the system only certain aspects are realistically considered using the lumped parameter approach employed in this research. The nonlinearities that are readily modeled by the lumped parameter approach constitute the geometry and constitutive relationship induced nonlinearity, including hysteretic behavior, noting that these properties all make an appearance in the load-deflection relationship for the mount and may be readily determined via experiment or flnite element analysis. In this paper we will shoe that under certain conditions, the nonlinearities involved in the hydraulic engine mounts can show a chaotic response.
Contamination Effect on the Electrical Resistivity of Gold Nanowires
Authors: Huang Q. , Lilley C. M. , Paing K. M.
Published: April 2008

Gold nanowires were patterned with e-beam lithography and fabricated with a gold film deposited by e-beam evaporation. Carbon and oxygen contaminants were found to be present mostly on the gold surface with x-ray photoelectron spectroscopy. Slight carbon contamination was indicated through the film thickness. Dimensions of the nanowires were measured with scanning electron microscopy, and the resistance of the wires was measured with a 2-probe stage at a low vacuum. Non-linear current-voltage curves were obtained, which was attributed to Joule heating. Further analysis, by restricting the bias voltage in a small range and negligible Joule heating, suggests that surface contamination can significantly affect the resistivity measurements of gold nanowires.
Modeling and Characterization of Nanowires With Microcantilever Beams
Authors: He J. , Lilley C. M.
Published: April 2008

Mechanical behavior of a nanowire-microcantilever beam structure under electrostatic actuation was studied using the FE method. A comparison for the resonant frequencies between a nanowire-microcantilever structure and a microcantilever only is presented. Several factors affecting the resonant frequency of the nanowire-microcantilever structure, such as actuation voltage and fabrication effects on geometries are discussed. Also, alignment effect of the nanowires with the microcantilever beam is investigated. This study can be utilized to predict Young's modulus of nanowires.
The Performance of an Enthalpy Recovery Wheel in Ventilation of CMU’s IW
Authors: Zhai Chaoqin , Archer David H. , Fischer John C.
Published: April 2008

The operating performance of an enthalpy recovery wheel exchanging heat and moisture between outside and exhaust air streams in the ventilation system of Carnegie Mellon University (CMU)'s Intelligent Workplace (IW) has been measured during the winter of 2006. The test has been performed using manufacture-installed instrumentation and supplementary temperature and humidity data loggers placed at various locations in the machine. The testing indicates that the operation of this wheel has reduced the heating load for ventilating the IW by 77%. Field testing performance agrees well with the lab testing data, which shows 82% heat recovery effectiveness under the same air flow settings used in field testing. The measured data have been analyzed to establish the heat balance over the wheel and to determine the effect of wheel purge on this balance. The measured data have also been analyzed on the basis of heat transfer principles to relate the performance of the wheel to its design parameters and operating conditions. Finally, the lessons learned in field testing of a commercial enthalpy recovery wheel are presented.
Experimental Observation of Liquid Water Formation in Cathode Side Gas Channel of a Transparent PEM Fuel Cell
Authors: Gan Mingfei , Chen Lea Der , Sui P. C.
Published: April 2008

This paper reports on an experimental observation of water formation in a proton exchange membrane fuel cell (PEMFC). A fuel cell assembly with transparent end plates showing the gas channels is used. The study shows that liquid water can be present inside the gas channel of the fuel cell at a relatively low current density condition. The presence of liquid water could be in the form of mist-flow, suspended droplets, and sporadic liquid-gas two-phase flows, depending on operating conditions of the fuel cell. The voltage of the transparent fuel cell degraded over time, which is thought to be a result due to contamination from the fabrication of the gas channel plates of the transparent fuel cell. Onsets of the liquid droplet formation in gas channels are compared to the qualitative descriptions of homogeneous and heterogeneous nucleation theories.
A Study of Self-Oscillation of a Model Vocal Fold System by Digital Image Correlation
Authors: Spencer M. , Siegmund T. , Mongeau L.
Published: April 2008

The understanding of the mechanics of the deformation behavior of vocal folds during flow-induced vibration is of central interest in studies of voice production. We have developed physical models of the vocal folds and connected such models to a flow supply system. The self-sustained oscillation of the vocal folds during phonation experiments is investigated using digital image correlation (DIC) techniques enabled through the use of a high-speed digital camera. A laser Doppler velocimeter was used to independently verify results from the DIC. The study reports on vibratory motion of the superior surface of the model vocal folds, and documents strain fields, and principal strains on that surface. From measured strains and the incompressibility assumption, the corresponding stress fields are computed. Strains on the vocal fold superior surface are quantified in dependence of varying subglottal pressures and flow rates.
Kinematically Designed Flexible Skins for Morphing Aircraft
Authors: Pastor Christine , Sanders Brian , Joo James J. , McCarty Robin
Published: April 2008

This investigation targeted the development of flexible materials that when combined with mechanized structures can enable large rigid body deformations of aircraft structures while maintaining its aerodynamic shape. The solution presented in this work focuses on determining the distribution of material properties to design such a skin using topology optimization techniques. The matrix material selected in this research is a representative Shape Memory Polymer (SMP), which is embedded with a reinforcing fiber. The fiber plays a dual role in that in addition to serving as a reinforcing element it also provides the means to activate the material response (e.g., changing cross link density) via resistive heating. In depth heat transfer analysis and experiments were conducted to understand power requirements and minimum spacing of the fibers to activate the desired material response.
Influence of Interconnect-Channel Shape on Heat and Mass Transfer in Anode-Supported Planar Solid Oxide Fuel Cells
Authors: Magar Yogesh N. , Manglik Raj M. , Jog Milind A.
Published: April 2008

The debate on inculcating effective design engineering learning – its fundamental conceptualization, application of theoretical constructs to model physical devices/systems, and development of tools for solving unstructured problems – and associated critical thinking has primarily focused on curricula issues. Little effort has been made to understand the cognitive underpinning of students that lends to success in this direction. This paper presents the findings of a transverse study to assess learning styles of undergraduate mechanical engineering students and their perceptions about design engineering. Survey results from a batch of sophomores and seniors are analyzed to ascertain: (i) aspects of learning styles that are conducive to design comprehension, and (ii) perceptions about design engineering that aid or impede such learning.
Reliability Evaluation Using Finite Element Method
Authors: Haldar Achintya , Huh Jungwon , Mehrabian Ali
Published: April 2008

A robust and sophisticated structural reliability evaluation procedure is presented. Reliability of any structural systems represented by finite elements can be evaluated using the algorithm. The authors called it a stochastic finite element method. Despite the significant recent progress in the risk and reliability analysis techniques, a large segment of the engineering profession is not familiar with them and thus fails to use them in everyday practices. The procedure is expected to fill that vacuum. Many sources of nonlinearity generally overlooked in the profession can be incorporated in the algorithm. Uncertainties in the load and resistance-related variables are modeled as realistically as possible. The estimation of the failure, probability implies that structural behavior just before failure needs to be captured as accurately as possible. The algorithm is capable of evaluating the probability of failure addressing all the related issues. With the help of four informative examples, the application potential of the procedure is clearly demonstrated. It is similar to the deterministic methods and is not expected to be complicated to the practicing engineers; thus, promoting its wider applications. It is shown that the observations made in laboratory experiments can be explained with the procedure. It is hoped that the method will be used in the future to estimate the reliability of real structures.
Analysis and Evaluation of a Two Engine Configuration in a Series Hybrid Electric Vehicle
Authors: Serrao Lorenzo , Pisu Pierluigi , Rizzoni Giorgio
Published: April 2008

The paper proposes the use of two engines as primary energy converter in a new generation refuse hauling vehicle with a series hybrid electric powertrain. The mission profile of such a vehicle in most U.S. cities is composed by an urban driving cycle for refuse collection, with low power requirements, followed by a highway section in which the vehicle travels at full power. Thus, while the engine must be sized for high power levels, it will be used at low loads for most of the time. The original Diesel engine is replaced with two smaller common-rail Diesel engines. The smaller engines are the same used in many mid-size European sedans and provide high peak efficiency. When the power required by the vehicle is low, the power request can be satisfied using only one of them, and the other one can be switched off. Thus, the only engine in use is running at high load (i.e., high efficiency) and the fuel consumption can be reduced in comparison with a single, bigger engine running at low load. An analysis of the typical vehicle driving cycle is carried out in order to evaluate the advantages of the dual engine architecture. The control strategy of the hybrid electric powertrain, which usually splits the power between the engine and the energy storage system, is extended with an additional degree of freedom, managing the power split between the two engines in order to minimize the instantaneous fuel consumption. A vehicle simulator is used to evaluate advantages and disadvantages of the proposed architecture, and to determine the best conditions for its implementation. Significant reductions of fuel consumption are obtained under proper conditions.
Squeeze-Film Phenomena in Microresonators Dynamics: A Mathematical Modeling Point of View
Authors: Jazar G. Nakhaie , Mahinfalah M. , Khazaei A. , Alimi M. H. , Christopherson J.
Published: April 2008

Oscillating microplates attached to microbeams is the main part of many microresonators. There are several body and contact forces affecting a vibrating microbeam. Among them are some forces appearing to be significant in micro and nano size scales. Accepting an analytical approach, we present the mathematical modeling of a microresonator a nonlinear model for MEMS are presented, which accounts for the initial deflection due to polarization voltage, mid-plane stretching, and axial loads as well as the nonlinear displacement coupling of electric force. The equations are nondimensionalized and the design parameters are developed. However, the main purpose of this investigation is to present an applied model to simulate the squeeze-film phenomena. We separate the two characteristics of the squeeze-film phenomena and model the damping and stiffness effects individually. Motion of the microplate and flow of the gas underneath is similar to the function of a decoupler plate in hydraulic engine mounts (Golnaraghi and Nakhaie Jazar 2001, Nakhaie Jazar and Golnaraghi 2002). More specifically, the squeeze-film damping is qualitatively similar to the function of decoupler plate in hydraulic engine mounts, which is an amplitude dependent damping (Christopherson and Nakhaie Jazar 2005). It means squeeze-film damping effect is a positive phenomenon to isolate the vibration of microplate from the substrate. Following Golnaraghi and Nakhaie Jazar (2001), and utilizing the aforementioned similarity, we model the squeeze-film damping force, fsd, by a cubic function, where the coefficient Cs is assumed constant and must be evaluated experimentally. In the simplest case, we present the following fifth degree function to simulate the spring force, fss, of the squeeze film phenomenon, simply because at low amplitudes, w ≈ 0, the fluid layer is not strongly squeezed and there is no considerable resistance. On the other hand, at high amplitudes, w ≈ d, there is not much fluid to react as a spring. In addition, speed is proportionally related to the squeezeness of trapped fluid. The coefficient ks assumed constant and must be evaluated experimentally. The coefficients cs and ks are dependent on geometry as well as dynamic properties of the fluid, but assumed to be independent of kinematics of the microbeam such as displacement and velocity. Therefore, this investigation presents two mathematical functions to describe stiffness and damping characteristics of squeeze-film phenomena in a reduced-order model of microresonators.
Molecular Sensors in Microturbine Measurement
Authors: Huang Chihyung , Gregory James W. , Nagai Hiroki , Asai Keisuke , Sullivan John P.
Published: April 2008

Microturbines have been studied for use in micro size engines as a fuel cell for power generation. These micro engines are designed to offer power output around a couple watts with a very small, compact size. However, there are a lot of difficulties for these small size turbines such as high friction, unstable rotor movement etc, that make the microturbines break down much earlier in their life cycle. These problems needed to be solved in order to improve the efficiency of microturbines. However, it is difficult to install micro sensors in the microturbine device for measurement. A novel technique of molecular sensor, known as pressure-sensitive paint and temperature-sensitive paint (PSP/TSP) has been developed to obtain the pressure and temperature field inside the microturbine device. The PSP sensors used in the experiments are PtTFPP/PolyTMSP for time-averaged pressure measurement, and PtTFPP/TMSP for phase-averaged pressure measurement. The TSP sensor of Ru(phen)3+/Polyacrylic is used for the temperature measurement. The PSP/TSP sensor is coated on glass slides and the glass slide is used as cover glass for the microturbine device. Pressure and temperature distributions inside the microturbine device have been successfully obtained with PSP and TSP sensors. The rotation speed for the microturbine varies from 1300 to 4000 rpm for different flow rates from 5 to 15 L/min for the time-averaged experiments. Phase-averaged results have been obtained with a laser triggering system at a rotation speed of 1400 rpm and volume flow rate of 17 L/min. The temperature map inside the microturbine has been acquired with the TSP sensor with a rotation speed from 1300 to 4000 rpm and flow rates from 5 to 15 L/min. The PSP/TSP sensor has been demonstrated with the feasibility of measuring the pressure and temperature field inside the microturbine device with high spatial resolution, both in time-averaged and phase-averaged measurements.
Periodic Motions of a Semi-Active Suspension System With MR Damping.
Authors: Luo Albert C. J. , Rajendran Arun
Published: April 2008

Periodic motions in a hysteretically damped, semi-active suspension system are investigated. The Magneto-Rheological damping varying with relative velocity is modeled through a piecewise-linear model. The theory for discontinuous dynamical systems is employed to determine the grazing motions in such a system, and the mapping technique is used to develop the mapping structures of periodic motions. The periodic motions are predicted analytically and verified numerically. The stability and bifurcation analyses of such periodic motions are performed, and the parameters for all possible motions are developed. This model is applicable for the semi-active suspension system with the Magneto-Rheological damper in automobiles. The further investigation on the Magneto-Rheological damping with full nonlinearity should be completed.
Advanced Process Model for Polymer Derived Ceramic Processing
Authors: Wang Xiaolin , Zunjarrao Suraj C. , Zhang Hui , Singh Raman P.
Published: April 2008

Pyrolysis of preceramic polymers allows a new type of ceramic materials to be processed at a relatively low temperature. The ceramics via polymer pyrolysis display a number of exceptional mechanical, thermal and chemical properties, including high thermal stability, high oxidation/creep resistance, etc. Moreover, they offer better geometrical accuracy compared to conventional ceramics. In addition, thermal induced pyrolysis of organometallic polymer precursors offers the possibility of net shape manufacturing at a lower temperature compared to traditional powder sintering process. The pyrolysis of polymer precursors involves curing of polymer precursors in which the polymer undergoes cross-linking to form a green body, followed by a pyrolysis stage that involves the formation of amorphous SiC and crystallization of SiC at a higher temperature. The source material changes phase and composition continuously during polymer pyrolysis based ceramic process. Chemical reactions and transport phenomena vary accordingly. To obtain ceramics with high uniformity of microstructure and species without crack, transport phenomena in material processing needs to be better understood and a process model needs to be developed to optimize the fabrication process. In this paper, a numerical model is developed, including heat and mass transfer, polymer pyrolysis, species transport, chemical reactions and crystallization. The model is capable of accurately predicting the polymer pyrolysis and chemical reactions of the source material. Pyrolysis of a sample with certain geometry is simulated. The effects of heating rate, particle size and initial porosity on porosity evolution, mass loss and reaction rate are investigated. Optimal conditions for the manufacturing are also proposed.
Absolute Nodal Coordinate Formulation Coupled Deformation Modes
Authors: Hussein Bassam A. , Sugiyama Hiroyuki , Shabana Ahmed A.
Published: April 2008

The finite element absolute nodal coordinate formulation (ANCF) leads to beam and plate models that relax the assumption of the classical Euler-bernoulli and Timoshenko beam and Mindlin plate theories. In these more general models, the cross section is allowed to deform and it is no longer treated as a rigid surface. The coupling between the bending and cross section deformations leads to the new ANCF-coupled deformation modes that are examined in this study. While these coupled deformation can be source of numerical and convergence problems when thin and stiff beam models are considered, the inclusion of the effect of these modes in the dynamic model is necessary in the case of very flexible structures. In order to examine the effect of these coupled deformation modes in this investigation, three different large deformation dynamic beam models are discussed. Two of these models, which differ in the way the beam elastic forces are calculated in the absolute nodal coordinate formulation, allow for systematically eliminating the coupled deformation modes, while the third allows for including these modes. The first of these models is based on a general continuum mechanics approach that leads to a model that includes the ANCF-coupled deformation modes; while the second and third methods that can be used to eliminate the coupled deformation modes are based on the elastic line approach and the Hellinger-Reissner principle. It is shown in this study that the inclusion of the ANCF-coupled deformation modes introduces geometric stiffening effects that can not be captured using other finite element models.
Transport Phenomena in Growth and Annealing of Laser Crystals
Authors: Fang H. S. , Cai D. , Zhang H. , Zheng L. L.
Published: April 2008

Cloudiness, bubble core defects, anomalous absorption, low-angle grain boundaries, and cracking are the main problems in the growth of high quality and large diameter (>7cm) Yb:S-FAP crystals utilizing the Czochralski method. The generation mechanism of these defects is highly related to transport phenomena in the growth system. In this paper, firstly, inductive, conductive and radiative heat transport phenomena are examined in the entire growth system. Then, an integrated modeling and experimental study is presented to determine an efficient means to eliminate or reduce crystal cracking during cooling. A process model has been developed to simulate the crystal cooling process. The effect of temperature distribution on thermal stress in the crystal during cooling is predicted by a simple but effective computational algorithm. With the relationship between the power change and crystal surrounding temperature change, the process model is further used to optimize power ramp-down profile to avoid cracking of the crystal during cooling-down process.
Mixed Mode Fracture in Brittle Materials for MEMS
Authors: Jonnalagadda Krishna , Chasiotis Ioannis , Friedmann Thomas
Published: April 2008

Planar defects such as cracks are rarely normal to the loading direction. To investigate the case of arbitrarily oriented cracks mixed mode I/II fracture experiments were conducted on amorphous diamond-like carbon (ta-C) thin films. The mixed mode I/II loading at the crack tip was obtained using oblique edge pre-cracks in uniform gage finite width tensile specimens. The pre-cracks were generated using microindentation in 1μm thick micro-tensile specimens. Uniaxial tensile tests were performed to measure the applied far-field stress at failure and a numerical solution was used to extract the stress intensity factor values. The results were compared against the maximum tensile stress (MTS) and maximum energy release rate (MERR) criteria for mixed mode fracture and the data showed good agreement.
Object-Oriented Environment for Dynamic Finite Element Modeling of Tires and Suspension Systems
Authors: Wasfy Tamer M. , Wasfy Hatem
Published: April 2008

An object-oriented graphical modeling environment, which includes integrated pre-processor, post-processor, and explicit time-integration finite element solver, for predicting the dynamic response of tires mounted on suspension systems is described. The pre-processor allows creating a hierarchical preliminary model of the system including the tire, suspension system, and terrain. The pre-processor includes an automatic mesh generator for generating the finite element (FE) model from the preliminary model. A tire preliminary object allows defining the tire cross-section, specifying the number of elements along the tire circumference, and defining beam elements along the circumference and meridian direction to model the various tire structural components such as the bead, ply, and belt. Other preliminary model objects include rigid body, linear spring-damper, leaf-spring, spherical joint, revolute joint, prismatic joint, and polygonal terrain. The user can also include support objects such as physical materials, and scalar graphs (for time-histories of known quantities). The preprocessor includes a model tree-editor which allows adding objects and changing their properties. The FE model is submitted to the solver which generates the system's motion time-history. The FE model consists of solid elements (including brick, beam, and truss), rigid bodies, and joints. The post-processor is used to display the analysis results, which include an animation of the motion of the system, coloring/contouring the tire using various scalar response quantities, and various types of graphs of response quantities (such as time-history, frequency and time-averaged graphs). The graphical output of the pre-processor and the post-processor can be displayed either on the computer screen or in immersive stereoscopic virtual-reality facilities. Users can control the visualization using the tree-editor.
Research on the Farfield Tonal Fan Noise at Small Mach Number
Authors: Zhu Shi-Jian , Wu Xian-Jun
Published: April 2008

The calculation model of the farfield tonal noise of a subsonic fan was studied in this paper in order to find the main sources of tonal noise. A full model and a simplified model, which neglects the acceleration noise, were brought out. Experiment was done to verify the full model and good fitness were found between the calculated result and the measured result. Numerical experiments were then done to compare among those two models and the Gutin formula, which calculates the acceleration noise of steady force. Results reveal that at small Mach number the simplified model, which takes only the fluctuating force into account, approximates exactly with the full model. Because the noise calculated by Gutin formula is very small, it is concluded that the tonal noise of a subsonic fan with the Mach number less than 0.2 is caused mainly by the fluctuating force. It gives a guideline to cut fan noise down.
Dynamic Analysis of Multi-Span Laminated Composite Coated Beams Carrying Multiple Accelerating Oscillators
Authors: Eftekhari S. A. , Farid M.
Published: April 2008

In this paper, the dynamics of a multi-span laminated composite coated beam subjected to a set of accelerating oscillators, by using a coupled finite element-differential quadrature method (DQM), is analyzed. First, using the finite element method, the governing equation of motion of the beam is reduced into a set of ordinary differential equations in time domain. Then DQM is employed to convert these equations together with the governing equations of motion of all moving oscillators into a set of algebraic equations. The efficiency and accuracy of the proposed technique are demonstrated by numerical examples. Furthermore, influence of various parameters such as lamina thickness, orientation of the coats, the number of spans, arrival time intervals, velocities and accelerations of the oscillators on the dynamic behavior of the system are investigated. The technique presented in this investigation is general and can be easily applied to any time-dependent problem.
Creep Behavior Analysis for a Bilayer Functional Graded Electrolyte Supported High Temperature Ceramic Fuel Cells
Authors: Ju Gang , Reifsnider Kenneth
Published: April 2008

Ceramic fuel cell, such as solid oxide fuel cell (SOFC), usually has three functional layers with one dense electrolyte in the middle and two porous electrodes on each side of it, which operates around 1000°C. Recent research activities in SOFC tend to lower the operation temperature to the range of 700°C-800°C due to improvement in mechanical properties, and reduction in costs. However, the state-of-the-art electrolyte yttria-stabilized zirconia (YSZ) under this reduced temperature produces relatively poor ionic conductivity. Ceria-based electrolyte is an excellent candidate in electrical properties under intermediate temperature range, even though it shows a lattice expansion by cerium reduction at the very low oxygen partial pressure occurring at the anode side. Hence, a bilayer yttria doped ceria (YDC) with thin YSZ protection at anode side is designed to maximize the ionic conductivity. However, this lattice expansion of cerium results in an internal stress under this SOFC consideration. In this paper, oxygen partial pressure dependent creep behavior of an edge crack at the bi-material interface (YSZ:YDC) is studied numerically. The steady state C* path independent integral is obtained from ABAQUS code. Bi-material and homogeneous cases are discussed under extensive creep. Finally, fracture analysis of an edge crack at the bilayer electrolyte is also investigated for homogeneous bilayer materials.
Maximizing Buckling Strength of Perforated Composite Laminates by Optimizing Fiber Orientation Using Genetic Algorithm
Authors: Cho H. K. , Rowlands R. E.
Published: April 2008

This paper demonstrates ability to significantly increase buckling loads of perforated composite laminated plates by synergizing FEM and a genetic optimization algorithm (GA). Plate geometry is discretized into specially-developed 3D degenerated eight-node shell isoparametric layered composite elements. General shell theory, involving incremental nonlinear finite element equilibrium equation, is employed. Fiber orientation within individual plies of each element is controlled independently by the genetic algorithm. Eigen buckling analysis is performed using the subspace iteration method. Available results demonstrate the approach is superior to more conventional methodologies such as modifying ply thickness or the stacking sequence of individual rectilinear plies having common fiber orientation through the plate.
Experimental Investigation of Thermocapillary Convection Near an Evaporating Meniscus
Authors: Dhavaleswarapu H. K. , Chamarthy P. , Garimella S. V. , Murthy J. Y. , Wereley S. T.
Published: April 2008

Experimental visualizations of the 3D convection patterns generated near an evaporating meniscus in a capillary tube are presented. Epi-fluorescent micro-particle image velocimetry (μPIV) using a two-cavity frequency doubled ND-YAG laser as the illumination source is employed to map the small-scale spatial flow fields near the meniscus. Methanol seeded with 0.5 μm polystyrene fluorescent particles is used as the experimental fluid. These fluorescent particles absorb light from the laser beam (λabs~542 nm, green) and emit a longer wavelength light ((λem~612 nm, red). Images obtained at a specified time delay (~20 ms) were interrogated to obtain vector flow fields.
A New Approach to Analyzing Reactions and Deflections of Beams: Formulation and Examples
Authors: Jong I. C. , Rencis J. J. , Grandin H. T.
Published: April 2008

This paper is aimed at developing a new approach to analyzing statically indeterminate reactions at supports, as well as the slopes and deflections, of beams. The approach uses a set of four general formulas, derived using singularity functions. These formulas are expressed in terms of shear forces, bending moments, distributed loads, slopes, and deflections of a beam having a constant flexural rigidity and carrying typical loads. These loads include (a) a bending moment and a shear force at the left, as well as at the right, end of the beam; (b) a concentrated force, as well as a concentrated moment, somewhere on the beam; and (c) a uniformly, as well as a linearly varying, distributed force over a portion of the beam. The approach allows one to treat reactions at supports (even supports not at the ends of a beam) as concentrated forces or moments, where corresponding boundary conditions at the points of supports are to be imposed. This feature allows one to readily determine reactions at supports as well as slopes and deflections of beams. A beam needs to be divided into segments for study if it contains discontinuities in slope at hinge connections or different flexural rigidities in different segments. Several examples are included to illustrate the new approach.
Hg Emission Modeling for a Blended Coal Particle
Authors: Puchayakala Madhu B , Annamalai Kalyan
Published: April 2008

The largest source of human-caused mercury air emissions in the U.S principle is from combustion coal, a dominant fuel used for power generation. The coal chlorine content and ash composition, gas temperature, residence time and presence of different gases will decide the speciation of Hg into Hg° (elemental form) and HgCl2 (oxidized form). The extent of oxidation depends on the concentration of chlorine in flue gases. In order to predict the % of oxidized Hg, a transient model for combustion of a coal particle is formulated including Hg reactions. The model assumes that mercury and chlorine are released as a part of volatiles in the form of elemental mercury and HCl. A three step reaction is implemented for the oxidation of mercury. The model investigates the effect of coal blend with feedlot biomass (FB or Cattle manure), ambient temperature, and particle size on the extent of mercury oxidization. Mercury oxidation (HgCl2) increased with increase in diameter of particle and FB % in blended fuel.
Nonlinear Identification of a Turbocharged Diesel Engine Compression System Dynamics by an Uncertain Volterra Representation
Authors: Xiros Nikolaos I. , Theotokatos Gerassimos P.
Published: April 2008

In the present paper, the dynamics of the compression system of the turbocharged Diesel engine is identified using an uncertain Volterra representation. The required results depicting the dynamic response of the compression system under various compressor running conditions and sinusoidal compression system valve excitations are produced by simulation using detailed mathematical modeling of the physical processes involved in the compression system. The simulation results are appropriately processed and the Volterra representation of the system dynamics is formulated.
Cascaded Robust Nonlinear Position Tracking Control of an Electrohydraulic Actuator: Sliding Mode and Feed Forward
Authors: Ayalew Beshahwired , Jablokow Kathryn W.
Published: April 2008

An approach to position tracking control based on a cascade of a nonlinear force tracking controller derived from a near input-output linearization framework and a simple feedback plus feed forward position controller is presented. The method exploits the cascade structure to employ a sliding mode pressure force tracking controller as inner-loop and the position tracking controller as an outer-loop. Furthermore, it is highlighted that Lyapunov backstepping analysis can be used to drive performance bounds and reveal trade-offs between the size of uncertainty and measurement errors and the tracking accuracy. The performance of the proposed cascaded robust controller is demonstrated with experiments and simulations on a test system that doesn't necessarily satisfy all of the assumptions made for controller derivation. In particular, a typical comparison of the robust and nominal cascade controllers shows the robust version can recover the performance of the nominal near IO linearizing controller. In addition, model simulation results are included to show the performance of the controller in the presence of some combinations of perturbations or difficult to estimate parameters such as valve coefficient, supply pressure, piston friction, and inclusion of servovalve spool dynamics.
An Adaptive Algorithm for Hybrid Electric Vehicle Energy Management Based on Driving Pattern Recognition
Authors: Gu Bo , Rizzoni Giorgio
Published: April 2008

In this paper we present a novel adaptation method for the Adaptive Equivalent fuel Consumption Minimization Strategy (A-ECMS). The approach is based on Driving Pattern Recognition (DPR). The Equivalent (fuel) Consumption Minimization Strategy (ECMS) method provides real-time suboptimal energy management decisions by minimizing the "equivalent" fuel consumption of a hybrid-electric vehicle. The equivalent fuel consumption is a combination of the actual fuel consumption and electrical energy use, and an equivalence factor is used to convert electrical power used into an equivalent chemical fuel quantity. In this research, a driving pattern recognition method is used to obtain better estimation of the equivalence factor under different driving conditions. A time window of past driving conditions is analyzed periodically and recognized as one of the Representative Driving Patterns (RDPs). Periodically updating the control parameter according to the driving conditions yields more precise estimation of the equivalent fuel consumption cost, thus providing better fuel economy. Besides minimizing the instantaneous equivalent fuel consumption, the battery State of Charge (SOC) management is also maintained by using a PI controller to keep the SOC around a nominal value. The primary improvement of the proposed A-ECMS over other algorithms with similar objectives is that it does not require the knowledge of future driving cycles and has a low computational burden. Results obtained in this research show that the driving conditions can be successfully recognized and good performance can be achieved in various driving conditions while sustaining battery SOC within desired limits.
Research on the Deep-Sea Pressure Adaptive Hydraulic Manipulators and Its Flow Distribution Control Technique
Authors: Zhang Yan , Gu Linyi , Wang Feng , Qiu Huiqiang , Yang Xirong , Chen Ying
Published: April 2008

How to realize the pressure-resist and seal of the components is the key point for the development of the deepsea hydraulic manipulators. In this paper, a novel hydraulic system with the outer-inner pressure balanced technique is presented. Another key problem is that oil supply could not provide enough oil for the actuators when the joints are operated simultaneously. So, an electro-hydraulic digital flow distribution method based on meter-in flow feedback for multiple actuators load sensing system is put forward to distribute flows when two or more actuators are operated together. The corresponding theoretical principle is analyzed and the performances are evaluated through simulations.
Adaptive Control of Active Magnetic Bearings to Prevent Rotor-Bearing Contact
Authors: Abulrub Abdul-Hadi G. , Sahinkaya M. Necip , Burrows Clifford R. , Keogh Patrick S.
Published: April 2008

Active Magnetic Bearing (AMB) systems offer various advantages over conventional bearings but due to their limited force capacity, with high levels of vibrations the rotor may come into contact with retainer bearings. Under conventional PID control, when a rotor comes into contact with its retainer bearings it remains in contact, until the rotor is run down and the system shut down. This may not be acceptable in some applications, such as aerospace and automotive applications. In this paper, a recursive open-loop adaptive control (ROLAC) algorithm is presented, as an extension of the existing open loop adaptive controller (OLAC), that updates the control force amplitude and phase at each sampling period for rapid response to changes in external excitations. The effectiveness of the algorithm in counteracting a sudden change of rotor unbalance is demonstrated by simulation and experimental results. The experimental system consists of a flexible 2 m long rotor with a mass of 100 kg supported by two radial active magnetic bearings. A simulation model of the system, including the contact dynamics, was used to assess the feasibility of the suggested controller before applying it to the experimental system. Depending on excitation levels, it is shown that the proposed controller is fast enough to prevent contact in most cases. If contact does occur the impact is minimized, and the method is able to recover the rotor position quickly. The proposed controller is implemented in real time and applied to the experimental system. It is shown that the controller works efficiently as predicted by the simulation studies.
An Investigation Into the Control of the Combustion Instability Using Acoustic Resonator for a Jet Engine
Authors: Jiang Jian , Liu Ke , Gu Fengshou , Yin Yao , Ball A. D.
Published: April 2008

Combustion instability in jet engines impedes efficient burning of fuel and degrades engine performance. Moreover, it can cause damage to the combustion chamber and even lead to a destructive failure in the operation of the engine. Considerable work has been carried out both theoretically and experimentally to understand the characteristics of this instability and develop control methods. These instability studies have been found based upon different on-line tests. However, they have incurred high costs and have often achieved limited results. This paper presents an acoustic method that relies on the coupling relationship between combustion and acoustics to monitor the behaviour of the instabilities. The appropriateness of using this acoustic method is confirmed by off-line experimental results. In addition, it is possible to implement the test at very low cost. Based on this investigation, a scheme has been developed to control the instabilities. It consists of a bank of resonators designed to match the resonant frequencies at which instability occurs. Test results show that this scheme produces effective suppression of the instabilities.
Free Transverse Vibrations of Orthotropic Composite Mindlin Plates or Panels With a Non-Centrally Bonded Symmetric Lap Joint (or Symmetric Doubler Joint)
Authors: Yuceoglu U. , Gu¨vendik O. , O¨zerciyes V.
Published: April 2008

The problem of the "Free Transverse Vibrations of Orthotropic Composite Mindlin Plates or Panels with a Non-Centrally Bonded Symmetric Lap Joint (or Symmetric Doubler Joint)" is theoretically analyzed and solved with some numerical results. The "Bonded Joint" system is composed of two dissimilar, orthotropic plate "adherends" non-centrally bonded and connected by a dissimilar, orthotropic "doubler" plate through a very thin and elastic adhesive layer. The "adherends" and the single "doubler" are taken into account as the "Mindlin Plates" with the transverse shear deformations and the transverse and the rotary moments of inertia. The adhesive layer is considered as a linearly elastic continuum with the transverse normal and shear stresses. The damping effects are neglected. The dynamic equations of the plate "adherends", the "doubler" plate and the adhesive layer in combination with the stress resultant-displacement expressions, after some algebraic manipulations, are finally reduced to a set of the "Governing System of the First Order Ordinary Differential Equations" in matrix form in terms of the "state vectors" of the problem. The aforementioned set of the "Governing Equations" is integrated by means of the "Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials)". Several mode shapes with their corresponding natural frequencies are presented for the "hard" and the "soft" adhesive cases. It was found that there are significant differences in mode shapes and natural frequencies corresponding to the "hard" and the "soft" adhesive cases. Additionally, some parametric studies such as the effects of the "Bonded Joint Length Ratio" and the "Bonded Joint Position Ratio" on the natural frequencies are included in this first study.
An Experimental Study of Ammonia-Water Bubble Absorption in a Large Aspect Ratio Microchannel
Authors: Jenks Jeromy , Narayanan Vinod
Published: April 2008

An experimental study of absorption of ammonia into a constrained thin film of ammonia-water solution is presented. A large aspect ratio microchannel with one of its walls formed by a porous material is used to constrain the thickness of the liquid film. An exit visualization section was used to confirm absorption of ammonia gas within the microchannel. Experiments were performed at a pressure of 1 bar and a fixed inlet temperature of the weak solution, for weak solution flow rates from 10 to 30 g/min, inlet mass concentrations from 0 to 15 percent, and gas flow rates between 1 and 3 g/min. Results indicate that the overall heat transfer coefficient changes little for lower inlet weak solution concentrations and for lower gas flow rates, but increases noticeably for a higher solution and gas flow rate. The solution side log-mean temperature distribution increases with an increase in inlet solution concentration. Absorber exit visualization revealed the presence of periodic ammonia bubbles, occurring in varying sizes and periods, indicating that improvements to the current design are necessary to ensure complete absorption within the microchannel.