bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Analysis of O2 Separating Membrane for a CO2-Emission-Free Power Process
Authors: Selimovic Faruk , Sunde´n Bengt , Assadi Mohsen , Selimovic Azra
Published: April 2008

The increased demand for clean power in recent years has led to the development of various processes that include different types of CO2 capture. Several options are possible: pre-combustion concepts (fuel de-carbonization and subsequent combustion of H2), post-combustion concepts (tail-end CO2 capture solutions, such as amine scrubbing), and integrated concepts in which combustion is carried out in pure a O2 or oxygen-enriched environment instead of air. The integrated concepts involve the use of oxygen-, hydrogen-, or CO2-separating membranes resulting in exhaust gas containing CO2 and water, from which CO2 can easily be separated. In contrast to traditional oxygen pumps, where a solid oxide electrolyte is sandwiched between two gas-permeable electrodes, a dense, mixed ionic-electronic conducting membrane (MIECM) shows high potential for oxygen separation without external electrodes attached to the oxide surface. Models for oxygen transport through dense membranes have been reported in numerous recent studies. In this study, an equation for oxygen separation has been integrated into a steady-state heat and mass transfer membrane model. Oxygen transfer through a porous supporting layer of membrane is also taken into account. The developed FORTRAN code has been used for numerical investigation and performance analysis of the MIECM and the oxygen transport potential over a range of operating conditions. Preliminary results indicate that a non-uniform temperature distribution, for a given set of oxygen inlet boundary conditions has considerable impact on the oxygen flux and membrane efficiency. Since the implementation of detailed membrane models in heat and mass balance calculations for system studies would result in excessive calculation time, results from this study will be utilized for the generation of correlations describing the oxygen transfer as a function of operating parameters such as temperature and partial pressure. This modeling approach is expected to improve the accuracy of system studies.
Thermionic Emission Energy Distributions From Nanocrystalline Diamond
Authors: Robinson Vance S. , Fisher T. S. , Show Yoshiyuki , Swain Greg , Pfeferkon Frank
Published: April 2008

Thermionic electron emission provides a means of direct energy conversion. Some of the benefits of thermionic power generation include: compactness, scalability, stability, lack of moving parts, and applicability to microscale devices. Taking advantage of these benefits requires the analysis and subsequent manufacturing of materials that emit electrons efficiently and at reasonable temperatures (<1000 °C). We report here on a study being performed to characterize the emission properties of such materials, namely, nanocrystalline diamond with hydrogen and oxygen termination. A hemispherical energy analyzer is used to measure the electron energy distribution from this nanostructured material at elevated temperatures. The effective work function and the presence of regions of differing work functions are determined. Measurements of thermionic emission energy distributions (TEEDs) at temperatures ranging from 573 to 778 °C are presented. The TEEDs show an intriguing development of multiple peaks at higher temperatures, possibly indicating instability in the emitter’s surface chemistry.
A Numerical Study of the Influence of Hydrogen Addition on Soot Formation in a Laminar Counterflow Ethylene/Oxygen/Nitrogen Diffusion Flame
Authors: Guo Hongsheng , Liu Fengshan , Smallwood Gregory J.
Published: April 2008

The influence of hydrogen addition to the fuel on soot formation in an ethylene/oxygen/nitrogen diffusion flame was numerically studied by simulation of three counterflow laminar diffusion flames at atmosphere pressure. The fuel mixtures for the three flames are pure ethylene, ethylene/hydrogen and ethylene/helium, respectively, while the oxidant is a mixture of oxygen and nitrogen. A detailed gas phase reaction mechanism including species up to benzene and complex thermal and transport properties were used. The soot inception and surface growth rates were, respectively, calculated based on benzene and HACA (H-abstraction and C2H2-addition) mechanisms. The predicted results for the three flames were compared and analyzed. It is indicated that although the addition of either hydrogen or helium to the fuel can reduce the soot volume fraction, the addition of hydrogen is more efficient. While the addition of helium reduces soot formation only through dilution, the addition of hydrogen suppresses soot formation through both dilution and chemical reaction effects. This conclusion is qualitatively consistent with available experiments. The simulations revel that the chemically inhibiting effect is caused by the decrease of hydrogen atom concentration in soot formation region, due to the displacement of the primary reaction zone, when hydrogen is added to the fuel.
Prediction of Endplate Bulging With and Without Inclusion of Physiological Swelling Pressure and Strain Dependent Permeability and Porosity
Authors: Williams J. R. , Natarajan R. N. , Andersson G. B. J.
Published: April 2008

Finite element models were used to understand how changes in physiological factors such as swelling pressure and strain dependent permeability alters the biomechanical characteristics of lumbar discs under compressive loads. Exclusion of these physiological factors increased endplate stresses, reduced endplate bulge and reduced nucleus and annulus stresses.
Control of Powder Flow Rate in Laser Metal Deposition Process
Authors: Thayalan Vishnu , Landers Robert G.
Published: April 2008

Precise regulation of powder flow in laser based manufacturing processes is critical to achieving excellent part quality. Control of powder flow in laser based manufacturing processes is challenging since low flow rates, where nonlinear effects are significant, are typically required. Also, gravity fed powder feeder systems have significant transport delays, making the control of powder flow even more challenging. This paper presents a control strategy for regulating the powder flow rate in a gravity fed powder feeder system. A dynamic model of the powder feeder system, including transport delay, is constructed and a digital proportional plus integral controller is designed. An observer is used to estimate powder flow rate using the powder feeder motor encoder signal. The control strategy is implemented in a Smith Predictor Corrector Structure to account for the material transport delay. Simulation and experimental results validate the controller.
Vibration Analysis and Control of the Quartz Rate Sensor
Authors: Wang Frank , Smith Marc
Published: April 2008

BEI Systron Donner’s family of quartz inertial sensors uses a one piece, micromachined inertial sensing element to measure angular velocity. These sensors produce an output signal proportional to the rate of rotation sensed. In this paper, the operation of the quartz rate sensor (QRS) is presented. A mathematical model of the quartz fork is extracted, and the vibration characteristics of the quartz fork are presented. In order to control the magnitude of the drive tines, an AGC/Oscillator (AGC: automatic gain control) loop is employed. The system response is analyzed using Matlab and Pspice. A switched capacitor (SC) circuit is used to realize the functions of full wave rectification (FWR), integration, and summation. The AGC level is controlled to within 0.3%/V dependency on the power supply. This fixes the scale factor of the QRS to the same level of power supply rejection.
Single Cell Opto-Electro-Mechanical Probing: A Feasibility Study
Authors: Desai A. V. , Haque M. A. , Scheuchenzuber W. J.
Published: April 2008

Mechanical, electrical and chemical signals from the environment direct influence the physiological activities and health of a cell. While the existing trend is to study these signals separately in their respective domains, they are actually inherently coupled. Here we explore the feasibility and merits of a new instrument that can measure, for the first time, externally applied (or internally generated) forces and electrical impedance of a single cell in real time. The pico-Newton resolution micro-instrument (1 mm × 1 mm in size) will be readily compatible with conventional optical/fluorescence techniques for opto-electro-mechanical probing. Force sensing operation is unaffected by the electrical and chemical nature of cell environment and the bio-impedance measurement scheme can automatically compensate for any non-cell specific sources of error. Studies on the effects of mechanical, electrical and chemical signals with real-time opto-electro-mechanical cell characterization will impact diagnosis and cure for various diseases of the heart, skin, intestines, nerves, oncology, bones, lung — to name a few. Long-term contributions would be novel lab-on-a-chip type diagnostic/therapeutic/drug discovery tools to monitor the bio-impedance of a single cell with respect to external stimuli (toxin, drug).
Force and Position Control of a Solenoid Injected Monopropellant Powered Actuator
Authors: Shields Bobby L. , Goldfarb Michael , Fite Kevin
Published: April 2008

This paper describes the control of a direct-injection, liquid monoproplellant powered actuation system, which was developed for the purpose of providing mechanical power to autonomous human-scale robots. The actuation system utilizes the catalytic decomposition of a monopropllant as a hot gas generator for powering a pneumatic actuator. Pressurization of the respective sides of a pneumatic actuator. is provided via solenoid injection valves, which control the flow of the monopropellant through a catalyst pack into the respective sides of the cylinder. Depressurization is provided by a three-way proportional spool valve, which proportionally exhausts one of the two cylinder chambers. This paper describes a controller that coordinates the control of the two discrete injection valves, together with the control of the proportional exhaust valve, in order to provide actuator force tracking. The controller is implemented on a prototype system with a closed-loop servo controller. Experimental results indicate effective position and force tracking.
Experimental Evaluation of a Track Tension Controller in Tracked Vehicles
Authors: Huh Kunsoo , Chung Chung Choo , Suh Mun-Suk
Published: April 2008

Track tension is closely related to the maneuverability of tracked vehicles and the durability of their tracks and suspension systems. The tension needs to be maintained at an optimum level throughout the maneuver in order to minimize the excessive load on the tracks and to prevent track peel-off from the sprocket. In this paper, a track tension control system is developed for tracked vehicles which are subject to various maneuvering tasks. It consists of track tension estimator, track tension controller and hydraulic unit. The tension around the idler and sprocket is estimated in real-time, respectively. Using the estimated track tension and considering the highly nonlinear vehicle characteristics, a fuzzy logic controller is designed in order to control the track tension in the vehicles. The performance of the proposed tension control system is verified through experimental field tests.
The Changing Role of FEA in the Product Development Process
Authors: Jain Suchit
Published: April 2008

In recent years, the benefits of using FEA or design analysis as part of conceptual design have become apparent. The direct involvement of design engineers in analyzing their own designs allows for quick turnaround times and ensures that design modifications indicated by analysis results are promptly implemented in the design progress. Used properly, it yields trustworthy results that are already driving efficiencies and cost savings in industries ranging from consumer goods to automotive. This paper will outline the advances in technology which have made this change possible.
A Bimodular Second-Order Orthotropic Stress Constitutive Equation for Cartilage
Authors: Klisch Stephen M. , Holtrichter Suzanne E. , Sah Robert L. , Davol Andrew
Published: April 2008

The design of tissue-engineered constructs grown in vitro is a promising treatment strategy for degenerated cartilaginous tissues. Cartilaginous tissues such as articular cartilage and the annulus fibrosus are collagen fiber-reinforced composites that exhibit orthotropic behavior and highly asymmetric tensile-compressive responses. They also experience finite deformations in vivo. Successful integration with surrounding tissue upon implantation likely will require cartilage constructs to have similar structural and functional properties as native tissue. Reliable stress constitutive equations that accurately characterize the tissue’s mechanical properties must be developed to achieve this aim. Recent studies have successfully implemented bimodular theories for infinitesimal strains (Soltz et al., 2000; Wang et al., 2003); those models were based on the theory of Curnier et al. (1995).
Effect of Welding Sequence on Welding-Induced-Alignment-Distortion in Fiber-Optic Device Packaging: Packaging of Butterfly Laser Diode Module
Authors: Lin Yaomin , Eichele Chad , Shi Frank G.
Published: April 2008

The welding-induced-alignment-distortion (WIAD) is a serious issue in fiber-optic packaging using laser welding, which may significantly affect the packaging yield. An elimination or minimization of WIAD is expected to be possible if the welding process and other packaging parameters can be optimized. This work attempts to evaluate the contribution of laser welding sequence to the WIAD for butterfly laser diode packages. A realistic physics based laser welding model incorporating the spatial and temporal characteristic of laser beam and thermophysical material properties and absorptivity was developed and incorporated in the 3-D finite element model for the thermal induced stresses/strains and the resulting fiber alignment distortion as a function of welding sequence. An experiment study was conducted and the results agreed well with the finite element model in the way welding sequence affects WIAD. Both numerical simulation and experimental investigation suggest that WIAD reduction can be significant if an appropriate welding sequence is employed in the packaging of butterfly laser diode packages.
Thermal Behavior of Silicon Heat Spreader Coated With Diamond Film
Authors: Lin T. W. , Wu M. C. , Peng C. H. , Chen P. L. , Hung Y. H.
Published: April 2008

In the present study, an experimental setup with stringent measurement methods for performing the natural convection from a horizontal heated chip mounted with a silicon heat spreader coated with diamond film has been successfully established. The parametric studies on the local and average effective heat transfer characteristics for natural convection from a horizontal smooth silicon wafer, rough silicon wafer or silicon wafer coated with diamond film spreader have been explored. The influencing parameters and conditions include Grashof number and spreader material with different surface treatment conditions. From the results, an axisymmetric bowl-shaped Nu profile is achieved, and the highest heat transfer performance occurs at the location near the rim of the heated surfaces for various heat spreaders. The local Nusselt number for a specified convective heat flux decreases along the distance from the disk rim toward the center. The local or average Nusselt number increases with increasing Grashof number for various heat spreaders. As compared with the average Nusselt number for smooth water surface (Ra=5.69nm), the heat transfer enhancements for rough silicon surface (Ra=516.61nm) and rough diamond surface (Ra=319.51nm) are 10.42% and 7.69%, respectively. Furthermore, new correlations for local and average Nusselt numbers for various heat spreaders are presented, respectively. As compared with the smooth silicon surface, the external thermal resistance for rough silicon surface and rough diamond surface are reduced to 91.18% and 90.73%, respectively; and the maximum thermal resistances for rough silicon wafer and silicon wafer coated with diamond film are reduced to 90.43% and 92.61%, respectively.
Micromechanical Evolutionary Elastoplastic Damage Model for Fiber-Reinforced Metal Matrix Composites With Fiber Debonding
Authors: Ju J. W. , Ruan H. N. , Ko Y. F.
Published: April 2008

A micromechanical evolutionary damage model is proposed to predict the overall elastoplastic behavior and interfacial damage evolution of fiber-reinforced metal matrix composites. Progressive debonded fibers are replaced by equivalent voids. The effective elastic moduli of three-phase composites, composed of a ductile matrix, randomly located yet unidirectionally aligned circular fibers, and voids, are derived by using a rigorous micromechanical formulation. In order to characterize the overall elastoplastic behavior, an effective yield criterion is derived based on the ensemble-area averaging process and the first-order effects of eigenstrains.
Instability of an Axial Leakage Flow-Induced Vibration of Thin Cylindrical Shells Having Freely Supported End
Authors: Fujita Katsuhisa , Kato Makoto
Published: April 2008

When thin cylindrical shells having freely supported end at the downstream side such as heat-shielding shells of afterburners, labyrinth air seals, annular structures in large diameter pipings and valves are subjected to axial leakage flows, an unstable vibration and a fatigue failure are apt to be occurred. In this paper, the unstable vibration of thin cylindrical shells is analytically investigated considering the fluid structure interaction between shells and fluids flowing through a narrow passage. The coupled equation of motion between shells and fluids is derived using the Flu¨gge’s shell theory and the Navier-Stokes equation. Especially, focusing on the higher circumferential vibrations, the unstable phenomenon of thin cylindrical shells is clarified by using root locus based on the complex eigenvalue analysis by using the mode functions obtained by the exact solution based on the Flu¨gge’s shell theory. The influence of shell-dimensions and so forth on the threshold of the instability of the coupled vibration of shells and flowing fluids are investigated and discussed.
Stiffness Evaluation and Vibration in a Tractor Gear
Authors: Bonori G. , Andrisano A. O. , Pellicano F.
Published: April 2008

The problem of gear noise in vehicles has been intensively studied in the past; however, recently the interest about this problem grew because of great restrictions in the laws regarding noise level and the increase of international competition. One of the most important vibration and noise sources is transmission error that excites the gearbox as a dynamic system, the gearbox surfaces, and connected components; the external box radiates noise. However, the current understanding of gear vibration remains incomplete, even though there is general agreement about the nature of the phenomenon. Vibrations are due to several sources: torsion resonance, impulsive or cyclic fluctuations in drive torque, gear mesh transmission error, local component vibration responses and fluctuations in the output torque demand. The concept of a vibrating system made of two gears is generally modeled through two wheels linked by the teeth mesh stiffness. In its simplest form, this model can simulate the classical linear resonance, i.e. the resonant frequency of the system. However, more complex phenomena such as parametric instabilities can be an important source of noise. In the present paper vibration problems in the gears of an industrial vehicle are investigated through the use of perturbation technique. A suitable software has been developed to generate the gear profiles in order to evaluate global mesh stiffness using finite element analysis.
Real-Time Species Distribution Profiling in PEFCs
Authors: Dong Q. , Kull J. , Mench M. M.
Published: April 2008

Knowledge of the species, current, and high frequency resistance distributions within a polymer electrolyte fuel cell (PEFC) is critical to enable prediction of the local performance and accurately quantify various species transport parameters. In micro and portable fuel cell systems, precise knowledge of steady state and dynamic water transport is especially important. This paper examines the distributed prifile of water vapor and other gas phase species in a PEFC, using a novel real-time technique for in situ species distribution measurement within the reactant flow channels of an operating PEFC. This is accomplished with an Agilent Real-Time Gas Analyzer (RTGA) that enables continuous profiling of changing species mole fractions at many locations along the anode and cathode flow paths, and enables detailed understanding of the time scales of the various multi-phase dynamic transport phenomena. Additionally, the periodic presence of liquid water droplets in the cathode can be observed at high current density with this technique.
Air Cooling Study of Transient Natural Convection Heat Transfer From Simulated Electronic Chips
Authors: Bhowmik H. , Tou K. W.
Published: April 2008

Experiments are performed to study the heat transfer characteristics during the power-on transient period from an array of 4 × 1 discrete heat sources in a vertical rectangular channel using air as the working fluid. The heat flux ranges from 1000 W/m2 to 5000 W/m2. For 2 mm protrusion of the heater, the effect of heat fluxes and chip numbers are investigated and observed that the transient Nul strongly depends on the number of chips. Correlations are presented for individual chips as well as for overall data in the transient regime.
A Virtual Lab for Composite Materials
Authors: Koenders E. A. B. , Dado E.
Published: April 2008

The development of a Virtual Lab for model composite materials in general and concrete in particular, is the main issue that is discussed in this paper. The contribution to the stimulation interactive research and development for technological innovations paves the way for exploitation of a Virtual Lab that facillitates the interactive development and integration of so-called multi-aspect models. The reason why concrete is considered as a multi-aspect material will be discussed with emphasis on the various levels of detail at which this material can be modelled. The complexity of the processes that are active at each of the particular levels originates the need for un-structuring commonly applied simulation models into Detailed Models controlled by a central Core Model. It establishes a sound basis for the development of a Virtual Modelling Laboratory (VML) In this paper, the focus will successfully be on concrete as a multi-aspect material, followed by the approach towards model integration. For this, the enabling ICT technologies will be discussed in detail. The paper ends with an overview on how innovations will benefit from the development of the VML as proposed abstract text here.
Experimental Studies on Hydrodynamic Resistance and Flow Pattern of a Narrow Flow Channel With Dimples on the Wall
Authors: Zhao J. B. , Chew Y. T. , Khoo B. C.
Published: April 2008

A systematic flow visualization study on flow structures inside dimples with different relative depths (h/d) and with round or sharp edges is carried out in the first part of this investigation; three flat test plates are made and each one has two dimples with the same print diameter (d) at 40 mm and the same h/d, which is set at 4%, 20% and 50% respectively. Then friction factor is measured on a test channel with two types of test plates. One has dimples array with h/d at 4% and round edge and the second is a flat plate used as reference; surface roughness can be changed for both test plates by painting and covering with water-proof paper. Flow visualization is also done on a dimple located at the center of the plate in the channel. Results show that shallow dimple (h/d=4%) produces non-separated flows at Reynolds number Reδ<1000 and there exists a rather small separation cavity flow at Reynolds number Reδ>1500. Dimple with h/d at 20% produces two symmetric vortices at Reδ<850, single vortex at Reδ ≈ 1000–1600 and symmetric horseshoe-liked vortex at Reδ>1700. Round edged dimple changes its fl pattern at different Reynolds number comparing to its sharp edged counterpart. For the dimple with h/d at 50%, at Reδ <1200 there is only one stable vortex; at Reδ>1800, it is unstable with its rotating direction changing frequently. In this part of preliminary work, dimpled plate with roughness reduces the friction factor by at least 2% in the flow channel comparing to the reference plate at Reynolds number ReDh ≈ 8,500~24,000. The friction factor curve of the channel with roughened dimpled plate approaches a hydraulically smooth channel with the increase of Reynolds number. No increase in friction factor is observed on the channel with dimpled plate having smooth surface in the comparison to the reference channel without dimples.
Multiobjective Genetic Algorithm Approach to the Optimization of a Rotating Flexible Arm With ACLD Patch
Authors: Fung Eric H. K. , Hau L. C. , Yau David T. W.
Published: April 2008

This paper describes the use of multi-objective genetic algorithm (MOGA) to solve an integrated optimization problem of a rotating flexible arm with Active Constrained Layer Damping (ACLD) treatment. The arm is rotating in a horizontal plane with triangular velocity profiles. The ACLD patch is placed at the clamped end of the arm. The design objectives are to minimize the total treatment weight, the control voltage and the tip displacement of the arm, as well as to maximize the passive damping characteristic of the arm. Design variables include the control gains, the maximum angular velocity, the shear modulus of the viscoelastic layer, the thickness of the piezoelectric constraining and viscoelastic layers, and the length of the ACLD patch. The finite element method, in conjunction with the Golla-Hughes-McTavish (GHM) method, is employed to model the ACLD flexible arm to predict its dynamic behavior, in which the effects of centrifugal stiffening due to the rotation are taken into account. Reasonable Pareto solutions are successfully obtained. It is shown that MOGA is applicable to the present integrated optimization problem.
Spreadsheets Solutions of the Boundary Layer Equations
Authors: Fakheri Ahmad
Published: April 2008

A classical problem in fluid mechanics and heat transfer is boundary layer flow over a flat plate. This problem is used to demonstrate a number of important concepts in fluid mechanics and heat transfer. Typically, in a basic course, the equations are derived and the solutions are presented in tabular or chart from. Obtaining the actual solutions is mathematically and numerically too involved to be covered in basic courses. In this paper, it is shown that the similarity solution and the solution to boundary layer equations in the primitive variables can easily be obtained using spreadsheets. Without needing much programming skills, or needing to learn specialized software, undergraduate students can use this approach and obtain the solution and study the impact of different parameters.
The Estimated Anisotropic Poroelastic Constants of an Osteon
Authors: Yoon Young June
Published: April 2008

Anisotropic poroelastic constants of an osteon are estimated by using the micromechanics. The drained elastic constants at the lacunar-canalicular porosity level are estimated by the effective moduli of the bone matrix containing the ellipsoidal cavities, the shape of lacunae. The undrained elastic constants are also calculated by the relation developed by Cowin (2003). These estimated anisotropic poroelastic constants will provide the database to develop an anisotropic poroelastic model of an osteon.
Active Control Algorithms for a Modified Hard-Mounted Isolation System
Authors: Wang Yung-Peng , Wu Yung-Chi
Published: April 2008

It is well known that the trend of current high-tech equipment and processes development is ultra-precision and high-speed. Thus, vibration becomes a significant issue for those high-tech equipment and processes. When the environmental vibration exceeds the requirements of the precision equipment, vibration control techniques should be employed to improve the accuracy and resolution of that equipment. There are two types of vibration control techniques. One is passive isolation system; the other is active isolation system. Passive isolation system can provide better performance for higher frequencies. Active isolation system is used to improve the isolation performance for lower frequencies. However, passive isolation system has bad performance around the natural frequency. In addition, it cannot eliminate the effects of onboard disturbances on the equipment. Therefore, active isolation system becomes the major technology in the applications of vibration control for precision equipment. In this paper, a modified hard-mounted isolation system is proposed to improve the performance of hard-mounted systems. In this system, a voice coil motor is placed in parallel with the passive element and used to eliminate the effects of onboard disturbances on the equipment. A piezoactuator is still utilized to isolate the environmental vibration from the equipment. Furthermore, an active control algorithm is developed to achieve the optimal performance of low vibration transmissibility and high stiffness. The results are verified by the numerical simulations.
Environmental Control of an Electronic System Integrated Into a Fighter Aircraft Pod
Authors: Engelhardt Michel
Published: April 2008

An Environmental Control System (ECS) concept is developed to control the temperature of an Electronic System (ES) and to cool the airborne system Electronic Units (EUs). These units are integrated into a Pod that is attached to the centerline station of a fighter aircraft. The objective of this paper is to describe the thermal control system concept used to control the ES bay air temperature, humidity, and pressure; and the cooling system used to cool the EUs. Another objective of this paper is to provide a summary of the thermal-fluid analytical models and the ECS performance predictions. The main components of the ECS are based on vapor cycle cooling. The EUs that support system management and recording are air-cooled. Ground operations are accomplished through the autonomous ECS thermal control of the ES and fan cooling of the EUs. Thermal analyses at aircraft operational altitudes and speeds predict that the ES temperature is controlled within ±5°C of its temperature at take-off by the ECS. ES bay temperatures are held between preset lower and upper bound ES temperatures during the required MIL-STD-210A tropical day without condensation of moisture in the ES bay. In addition, thermal analyses indicate that the EUs are cooled throughout ground and airborne operation to ensure that electronic components are below their manufacturers’ rated temperature requirements.
Variability of Nanoindentation Responses of Bone and Artificial Bone-Like Composites
Authors: Oyen Michelle L. , Ko Ching-Chang
Published: April 2008

Nanoindentation is a popular technique for measuring the intrinsic mechanical response of bone and has been used to measure a single-valued elastic modulus. However, bone is a composite material with 20–80 nm hydroxyapatite plates embedded in a collagen matrix, and modern instrumentation allows for measurements at these small length scales. The present study examines the indentation response of bone and artificial gelatin-apatite nanocomposite materials across three orders of magnitude of lengthscale, from nanometers to micrometers, to isolate the composite phase contributions to the overall response. The load-displacement responses were variable and deviated from the quadratic response of homogeneous materials at small depths. The distribution of apparent elastic modulus values narrowed substantially with increasing indentation load. Indentation of particulate nanocomposites was simulated using finite element analysis. Modeling results replicated the convergence in effective modulus seen in the experiments. It appears that the apatite particles are acting as the continuous (“matrix”) phase in bone and nanocomposites.
Correlation of 3-D Precision Machined Surface Topography With Frictional Response
Authors: Singh Ramesh , Kalil Rick , Melkote Shreyes N. , Hashimoto Fukuo
Published: April 2008

Precision surface finishes are used in a wide variety of applications. From bearing races and rolling elements to parallel slide ways, the functional characteristics of these surfaces are critical to their performance. Experimental trial and error has shown that certain surfaces outperform others in certain applications, but the specific surface characteristics that make this true are yet to be fully understood. The present paper addresses this issue through a detailed three-dimensional topographic analysis of different precision finished surfaces and correlation with their frictional response. Experiments are conducted to investigate the effect of surface type (Isotropic Finished, Ground, Hard Turned and Honed) and relative surface speed on the coefficient of friction in rolling/sliding contact. Utilizing white light interferometry measurement of the surfaces, different 3-D topographic parameters such as RMS deviation, density of summits and texture direction are obtained and their correlation with the experimentally obtained coefficients of friction is examined. Results show that the 3-D amplitude parameter Sq (RMS deviation of surface) and spatial parameter Sds (density of summits) play an important role in determining the frictional behavior of the surfaces studied.
Application of Advanced Signal Processing Methods to Automotive Systems Testing
Authors: Rohde Steve M. , Williams William J. , Rohde Mitchell M.
Published: April 2008

During the past twenty years there have been rapid developments in the creation and application of mathematical computer-based capabilities and tools (e.g., FEA) to simulate and synthesize vehicle systems. This has led to the concept of virtual product development. In parallel with the development of these tools, an equally sophisticated set of tools have been developed in the area of advanced signal processing. These tools, based upon mathematical and statistical modeling techniques, enable the extraction of useful information from data and have application throughout the entire vehicle creation process. Moreover, signal processing bridges the gap between the “virtual” and the “real” worlds — an extremely important concept that is changing the entire nature of what is thought of as “testing.” This paper discusses the use of advanced signal processing methods in vehicle creation with particular emphasis on its use in vehicle systems testing. Modern Time Frequency Analysis (TFA), a technique that was specifically designed to study transient signals and was in part pioneered by one of the authors (WJW), is highlighted. TFA expresses a signal jointly in time and frequency at very high resolution and as such can often provide profound insights. Applications of TFA to vehicle systems testing are presented related to Noise, Vibration, and Harshness (NVH) that enable sound quality analyses. For example, using TFA predictive models of consumer preferences for transient sounds that are useful to the automotive engineer in testing and modifying new vehicle subsystem designs are discussed. Other applications that are discussed deal with brake pedal feel, and characterizing vehicle crash signals. In the latter case TFA has resulted in some unique insights that were not provided by conventional statistical and mathematical analyses.
Numerical and Experimental Investigations on a Centrifugal Pump With and Without a Vaned Diffuser
Authors: Pavesi G. , Ardizzon G. , Cavazzini G.
Published: April 2008

Extensive research on centrifugal pumps was designed to investigate the impact of a diffuser on flow field instabilities and the noise generated by these instabilities. Activity was based upon a coupled use of measurements and 3D fully-viscous, unsteady computations. The test model was a seven-blade pump-turbine, used as a pump. Fitted with a vaneless diffuser, and two vaned diffusers with twenty-two adjustable, guide-diffuser vanes, and a return channel with eleven continuous vanes. Diffusers were equipped with eight pressure sensors in the adjustable guide-diffuser vanes, and nineteen pressure taps in the continuous vanes. To establish a link between the flow field structure and acoustic radiation, flow velocity was measured in the vaneless part of the diffuser. Piezoelectric transducers, placed flush with the wall, were used to measure pressure fluctuation inside the blade channels. Signal analysis was carried out in the frequency domain. Results showed the jet-wake flow pattern induced an unstable vortex, which influenced flow discharging from the adjacent passage, and destabilized jet-wake flow in the passage. This instability caused a periodic fluctuation at the discharge of the impeller. Fluctuations were found to be coherent from blade to blade, and to possess a rich harmonic content. Numerical analyses did not fully confirm these results.
Effect of Vortex Flow on Heat Transfer to Combustion Chamber Wall
Authors: Jahangirian S. , Abarham M. , Ghafourian A. , Saidi M. H.
Published: April 2008

A new experimental facility was designed, fabricated and tested to model and study the effect of bidirectional swirl flow on the rate of heat transfer to combustion chamber walls in many applications. Heat transfer to combustion chamber walls is an unwanted phenomenon. Reduction of this heat transfer can result in time and cost saving methods in design and fabrication of combustion chambers. The experimental study was performed by using propane and air with oxygen as fuel and oxidizer respectively. The location of injection ports and geometry of combustion chamber are flexible and could be varied. Tests were performed with different mass flow rates of fuel and oxidizer. For the same flow rates and with the presence of bidirectional flow, a wall temperature reduction of up to 50% was observed. In cases where only some of the oxidizer was injected from the chamber end to generate the bidirectional swirl flow, highest efficiency and lowest wall temperature existed. This can be due to better mixing of fuel and oxidizer and absence of hot spots in the combusting core. Further development of this technique enables combustion chamber manufacturers in a wide spectrum of industries such as gas turbine manufacturers to use less expensive and more available material in their production of combustors.
An Electronic Model for Transport in Fuel Cell Systems
Authors: Shewchun John , Lai Ming-Chia , Bhaskarachari Santosh A.
Published: April 2008

Existing descriptions for the current-voltage characteristics of a fuel cell are based on classical thermodynamics, which treat the cell as a simple reversible chemical reaction ( A + B ↔ C + D). The cell voltage is given through the Nernst equation in terms of the concentrations of the reacting species. However, cell current can only be expressed phenomenologically through voltage losses due to charge and mass transport, which are termed “polarizations.” The main component of the cell current (the operating region) is controlled by the diffusion gradients at the two porous electrodes (anode and cathode) and is expressed through Fick’s law.
Solvent Free Fabrication of Biodegradable Porous Polymers
Authors: Wang Xiaoxi , Li Wei , Kumar Vipin
Published: April 2008

Biodegradable porous polymers with interconnected pores of sub-micrometers to a few hundred micrometers find many applications in emerging technology areas such as tissue engineering, controlled drug delivery, and biochemical sensors. However, most of the current fabrication processes involve organic solvents and chemical blowing agents that may cause environmental concerns and leave residues harmful to biological cells. This paper presents a solvent free fabrication approach for biodegradable porous polymers. Ultrasound cavitation is introduced after the solid state foaming process to produce open cell structures. The material used in this study is polylactic acid (PLA). It belongs to a family of biodegradable polymers that can be used for tissue engineering scaffolds. In order to identify suitable conditions to apply ultrasound, a saturation and foaming study is conducted for the PLA-CO2 gas polymer system. The effects of various process variables are discussed.
Material Removal and Dimensional Integrity of Green Machined W-Ni-Fe
Authors: Sunanta Owat , Cohen Paul H. , Atre Sundar
Published: April 2008

In this research, the mechanism of material removal in green machining of unsintered tungsten alloy (W-Ni-Fe) was explored via orthogonal cutting. Parameters related to tool design (e.g. forces, stresses, and energy required during material removal processes at different settings) were calculated and compared. Dimensional integrity of production machining in pre-sintered tungsten alloy was also investigated via drilling and end-milling. The results, then, were compared with the conditions after sintering. Statistical analyses were used to quantify and explain the relationships among potential parameters. This research utilizes designed experiments and data analyses to investigate the material removal mechanism in green machining and the dimensional integrity of production machining pre-sintered tungsten alloy versus its status after sintering.
Analysis of a Common Cause Hypothesis in a Forensic Product Defect Analysis
Authors: Carnahan James V. , Ruhl Roland L. , Strauss Mark G. , Genson Laura R.
Published: April 2008

Forensic analysis of an accident involving machinery or equipment requires the engineering investigator to determine what role the equipment played in the accident. That analysis involves consideration of “defect” and “proximate cause,” items that have very specific legal meaning. The authors will discuss legal requirements relating to the investigator’s role in product defect analysis and will provide examples of scientific methodology deemed admissible in Federal Court. Two case examples are given where a reliability analysis based on the Weibull failure distribution was used to support, in part, the expert’s conclusions.
Multisensor Fusion Using Fuzzy Logic for an Integrated Smart Health Monitoring System
Authors: Mohanty Amit , Leach Chris , Mahajan Ajay
Published: April 2008

This paper presents a generic model for an integrated smart health monitoring system for infrastructures using multisensor fusion and condition assessment sheets. Though various techniques for health monitoring have been discussed extensively in the literature, little attention has been given to obtain high quality data from the measurement and sensing system by using an intrinsic knowledge base. The method proposed in this paper uses measurement data from different types of sensors with different resolutions and fuses it together based on the confidence in them derived from information not typically used in traditional data fusion methods. Examples of such information are operating temperature, frequency range, fatigue cycles, etc. These are fed as additional inputs to a fuzzy inference system (FIS) that has predefined membership functions for each of these variables. The outputs of the FIS are weights that are assigned to the different sensor measurement data that reflect the confidence in the sensor’s behavior and performance. A modular approach is adopted for the data fusion system. It allows adding or deleting a sensor, along with its fuzzy logic controller (FLC), anytime without affecting the entire data fusion system. The time history of problems and solutions taken to correct them are stored as a condition assessment sheet (CAS) that shows the health of each sensor and the entire measurement system at a glance. This work finds applications in the health management of civil infrastructures, power plants, airplanes and rocket/shuttle test facilities.
Determination of Machine Tool Frequency Response Function During Cutting
Authors: Kushnir Emmanuil
Published: April 2008

The dynamic compliance (frequency response function - FRF) of a machine tool structure in the cutting zone under a cutting load is one of the major dynamic characteristics that define a machine’s cutting performance. The roundness and surface finish define the quality of the manufactured parts. These characteristics are developed during finishing and semi-finishing cuts. The kinowledge of machine tool dynamic compliance, defined in these steady-state cutting conditions, ensures parts quality and increase in machine tool productivity. The dynamic compliance is usually evaluated in tests, which are performed by means of hammers or vibrators (exciters). During these tests the machine does not cut and the machine components do not move relative to each other. The loads in the machine during cutting are defined by different internal and external sources that are acting in different points of the machine and in different directions. The real spectrum and frequency range of these forces is unknown. Experimental data acquired by different types of tests clearly show the difference in dynamic compliance for the same machine tool during cutting and idling. The machine tool dynamic tests performed by different types of external exciting devices do not take in consideration the real load conditions and interactions of moving components, including the cutting process itself and external sources of vibration. The existing methods of experimental evaluation of machine tool dynamic compliance during steady-state cutting condition require dynamometers to measure the cutting force and a special sensor to measure relative displacement between the cutting tool and workpiece. The FRF that is computed from these measurements represents a dynamic characteristic of the close loop system (machine structure and cutting process) and only under certain conditions may be considered as FRF of machine tool structure itself. The theory of stationary random processes allows defining the cutting conditions, under which the obtained data represent the FRF of machine tool structure, and provide estimations of random and bias errors of this evaluation. The simplified methodology of FRF estimation, based only on measurement of the spindle and tool vibration, is also presented in this paper. This methodology is used on an assembly line to obtain FRF for machine tools performance comparison and quality assurance.