bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Process Parameters on Carbon Nanotube Synthesis by Plasma Enhanced Chemical Vapor Deposition (PECVD)
Authors: Kim Sungwon S. , Fisher Timothy S.
Published: April 2008

Plasma-enhanced chemical vapor deposition (PECVD) offers a variety of advantages in the synthesis of carbon nanotubes in that several critical synthesis parameters can be controlled independently. In the present study, the effects of reacting gas composition, catalyst film thickness and bias voltage are investigated. Carbon nanotube samples are grown in a microwave PECVD chamber on clean silicon substrates. Gas composition is varied from carbon-rich to carbon-lean by controlling the methane flow rate. The results indicate that gas-phase composition profoundly affects the synthesized material, which is shown to be randomly oriented nanotube mats for moderate-to-rich gas mixtures and non-tubular carbon for very lean mixtures. The non-tubular content is shown to contain disordered and graphitic bonding by Raman spectrometry. Vertically aligned nanostructures are obtained under the presence of bias voltage.
Dielectrostriction and Piezoresistance Response in Liquid Polymers
Authors: Peng Yiyan , Edmiston John , Shkel Yuri M.
Published: April 2008

Variations of dielectric and resistive responses of a material with deformation are called dielectrostriction and piezoresistance respectively. Both phenomena have the same microscopic foundation — they involve the change of relative positions of polarizable or conductive species, leading to change in the material’s electric properties. Since both dielectrostriction and piezoresistance are determined by the pair distribution function of inclusions, these two phenomena are sensitive to a material’s microstructure, which renders them effective for monitoring liquid polymer and polymer suspension processing and mixing. In this study, a planar sensor is implemented to detect the dielectrostriction effect in shear flow of pure silicone elastomer and piezoresistance effect in silicone/graphite suspensions. In both measurements, the electric responses are found to be scaled with the flow-induced stresses, which constitute new approaches to study the rheological properties of bulk materials and suspensions and compliment each other for revealing the microstructure in various systems.
Demonstration and Characterization of a Multi-Stage Silicon Microturbine
Authors: Lee Changgu , Fre´chette Luc G.
Published: April 2008

This paper presents the experimental testing and characterization of a microscale radial outflow turbine with four concentric stages. The device is a five layer structure composed of shallow and deep reactive ion etched silicon wafers and an ultrasonically drilled Pyrex glass wafer that are assembled using anodic and fusion bonding techniques. They enclose a 4mm diameter rotor that was spun up to 330,000 rpm and produced roughly 0.1W of mechanical power from each stage totaling 0.38W with 0.75 atm differential pressure across the microturbine. Modeling of the turbine based on a mean line analysis with loss correlations extracted from CFD suggests a turbine isentropic efficiency of 35% and Re=266 at the maximum speed. The pressure distribution across the blades rows was measured and showed close agreement with the calculation results. Using the model, the microturbine is predicted to produce 3.2 watts with an isentropic efficiency of 63% at a rotor speed of 1.1 million rpm.
Stereolithography of PEG Hydrogel Multi-Lumen Nerve Regeneration Conduits
Authors: Arcaute K. , Ochoa L. , Mann B. K. , Wicker R. B.
Published: April 2008

Peripheral nerve regeneration conduits available today are single lumen conduits. Multi-lumen conduits offer advantages over currently available conduits in that multiple lumen better mimic the natural structure of the nerve, provide a greater surface area for neurite extension, and allow for more precisely located growth factors or support cells within the scaffold. This work describes and demonstrates the use of the stereolithography (SL) rapid prototyping technique for fabricating multi-lumen nerve guidance conduits (NGCs) out of photopolymerizable poly(ethylene glycol) (PEG). NGCs were fabricated from PEG-dimethacrylate (PEG-dma) molecular weight 1000 with 30% (w/v) aqueous solution and 0.5% (w/v) of the photoinitiator Irgacure 2959. The selection of the PEG-dma and photoinitiator concentration was based on previous work [13]. A 3D Systems 250/50 SL machine with a 250 μm laser beam diameter was used for the experiments in a slightly modified process where the NGCs were fabricated on a glass slide within a small flat-bottom cylindrical container placed on top of the SL machine’s original build platform. SL successfully manufactured three-dimensional, multi-layered and multi-material NGCs with varying overall NGC lengths and lumen sizes. Minimum lumen size, spacing, and geometric accuracy were constrained by the laser beam diameter and path, curing characteristics of the polymer solution, and UV transmission properties of the polymer solution and cured PEG-dma. Overall lengths of the NGCs were constrained by the ability of the conduit to self-support its own construction. Multiple material conduits were demonstrated by varying the build solution during the layering process. In summary, SL shows promise for fabrication of bioactive NGCs using PEG hydrogels, and the use of SL in this application offers the additional advantage of easily scaling up for mass production.
Transparency Extension in Haptic Interfaces via Adaptive Dynamics Cancellation
Authors: McJunkin Samuel , Speich John E. , O’Malley Marcia K.
Published: April 2008

Haptic interfaces are a class of robotic manipulators that display force feedback to enhance the realism of virtual environment displays. However, these manipulators often fail to effectively replicate the real world environment due to dynamic limitations of the manipulator itself. The ratio of the simulated to transmitted environment impedance is defined as the transparency transfer function (TTF), and can be used to quantify the effectiveness of a haptic device in displaying the simulated environment. The TTF is ideally equal to one for the bandwidth of human proprioception. In this work, a method is presented that increases TTF bandwidth via cancellation of dynamics with an adaptive model. This adaptive model is based on the kinematics and dynamics of a PHANToM haptic interface with assumed joint stiffness and damping added. The Lagrangian of the PHANToM is reformulated into a regressor matrix containing the state variables multiplied by a parameter vector. A least-squares approach is used to estimate the parameter vector by assuming that errors in force output are due to the manipulator dynamics. The parameter estimate is then used in the original model to provide a feed-forward cancellation of the manipulator dynamics. Software simulation using data from passive user interactions shows that the model cancellation technique improves bandwidth up to 35 Hz versus 7 Hz without compensation. Finally, this method has a distinct advantage when compared with other compensation methods for haptic interactions because it does not rely on linear assumptions near a particular operating point and will adapt to capture unmodeled features.
Hydrogen Production From Ethanol: A Thermodynamic Analysis of a Novel Sorbent Enhanced Gasification Process
Authors: Mahishi Madhukar R. , Sadrameli Mojtaba S. , Vijayaraghavan Sanjay , Goswami Dharendra Y.
Published: April 2008

A novel biomass hydrogen production technique by integrating gasification and absorption reactions has been suggested. The method involves gasification of biomass in presence of a CO2 sorbent. Ethanol was used as the model biomass compound and CaO was the representative sorbent. Equilibrium modeling was used to determine the product gas composition and hydrogen yield. The analysis was done using ASPEN PLUS software (version 12.1) and Gibbs energy minimization approach was followed. The effects of temperature, pressure, steam/ethanol ratio and CaO/ethanol ratio on product yield were investigated. Three case studies were conducted to understand the effect of sorbent addition on hydrogen yield. Finally a simple energy analysis was carried out to determine the energy consumption and efficiency of sorbent enhanced ethanol gasification.
Towards an Effective Approach to Reduce Environmental Burdens via Process Planning
Authors: Roma´n Felipe , Bras Bert
Published: April 2008

In order for companies to attain greater reductions in environmental burdens during manufacturing operations, they need to consider environmental aspects during their initial product development stages. This places an additional burden on designers and process engineers who already need to meet multiple objectives within tight constraints. Consequently, environmental aspects are rarely considered in their decision making process. Thus, if environmentally conscious decisions are to be made, the utilization of existing information must be maximized. In response to this problem we propose an approach for storing and reusing environmentally-related process information of similar component process plans via environmental process model templates. These templates will contain standard environmental information and models associated with manufacturing operations and thus should effectively support environmentally conscious decisions in component process planning and eventually design. We illustrate how the templates can be developed for a gear process planning example.
Material Strengthening Mechanisms and Their Contribution to Size Effect in Micro-Cutting
Authors: Liu Kai , Subbiah Sathyan , Melkote Shreyes N.
Published: April 2008

The specific cutting energy in machining is known to increase nonlinearly with decrease in uncut chip thickness. It has been reported in the literature that this phenomenon is dependent on several factors such as material strengthening, ploughing due to finite edge radius, and material separation effects. This paper examines the material strengthening effect where the material strength increases as the uncut chip thickness decreases down to a few microns. This increase in strength has been attributed to various factors such as strain-rate, strain gradient and temperature effects. Given that the increase in material strength in the primary and secondary deformation zones can occur due to many factors, it is important to understand the contributions of each factor to the increase in specific cutting energy and the conditions under which they are dominant. This paper analyzes two material strengthening factors: (i) the contribution of the decrease in the secondary deformation zone cutting temperature, and (ii) strain gradient strengthening, and their relative contributions to the increase in specific cutting energy as the uncut chip thickness is reduced. Finite Element (FE) based orthogonal cutting simulations are performed using aluminum 5083-H116, a work material with a small strain-rate hardening exponent, thus minimizing strain-rate effect. Suitable cutting conditions are identified under which the temperature and strain gradient effects are dominant. Orthogonal cutting experiments are used to validate the model in terms of the cutting forces. The simulation results are then analyzed to identify the contributions of the material strengthening factors to the size effect in specific cutting energy.
Modeling, Parameter Identification, and Validation of Reactant and Water Dynamics for a Fuel Cell Stack
Authors: McKay D. A. , Ott W. T. , Stefanopoulou A. G.
Published: April 2008

This paper describes a simple two-phase flow dynamic model that predicts the experimentally observed temporal behavior of a proton exchange membrane fuel cell stack and a methodology to experimentally identify tunable physical parameters. The model equations allow temporal calculation of the species concentrations across the gas diffusion layers, the vapor transport across the membrane, the degree of flooding in the electrodes, and then predict the resulting decay in cell voltage over time. A nonlinear optimization technique is used for the identification of two critical model parameters, namely the membrane water vapor diffusion coefficient and the thickness of the liquid water film covering the fuel cell active area. The calibrated model is validated for a 24 cell, 300 cm2 stack with a supply of pressure regulated pure hydrogen.
QFD and CE as Methodologies for a Quality Assurance in Product Development
Authors: Alcantara Jose´ Ricardo , Hatakeyama Kazuo
Published: April 2008

Quality Function Deployment — QFD combined with Concurrent Engineering — CE as a support tool for the competitive strategy on product development is devised. In this study, beyond the proposed method, it is intended to develop relations with innovational models, arrangements of innovation and technology transfer, learning in organizations, and how the diffusion of knowledge occurs. QFD can also be one those main tools of CE as this identifies the customer’s main requirements translating into the features required for products. The field survey of exploratory and descriptive type, using the questionnaire as data collection technique, was carried out in the manufacturing companies in the fast growing sectors of automobile industries in the State of Parana located in the Southern of Brazil. The selection of sample companies was made intentionally to guarantee of return of answer through the accessibility criteria. The reasons for this fact that can be pointed out are: the use of “home made” methodology to fulfill customer’s requirements, unknowing of the methodology, and the lack of adequate training to use QFD. It is expected that the results of findings, if disseminated adequately among local companies, will help to enhance the competitiveness performance beyond the local market scenario.
Free Transverse Vibration of Thin Rotating Disks: Nonlinear Analysis
Authors: Hamidzadeh Hamid R.
Published: April 2008

An analytical method is adopted to determine natural frequencies for a nonlinear spinning disk. The disk is assumed to be isotropic and rotating under steady state conditions. The effects of amplitude and rotating speed on natural frequencies are determined. The developed procedure is also capable of analyzing natural frequencies of linear free vibration, which is independent of amplitude. Attention is confined to determine natural frequencies for different numbers of nodal diameters. The developed procedure does not consider modes of vibration corresponding to nodal circles. Validity of this procedure is verified by comparing some of the computed results with those established for certain cases.
Bounds on Two-Phase Flow: Part I — Frictional Pressure Gradient in Circular Pipes
Authors: Awad M. M. , Muzychka Y. S.
Published: April 2008

Simple rules are developed for obtaining rational bounds for two-phase frictional pressure gradient. Both the lower and upper bounds are based on the separate cylinders formulation. The lower bound is based on turbulent-turbulent flow that uses the Blasius equation to represent the Fanning friction factor. The upper bound is based on an equation that represents well the Lockhart-Martinelli correlation for turbulent-turbulent flow. The model is verified using published experimental data of two-phase frictional pressure gradient versus mass flux at constant mass quality. The published data include different working fluids such as R-12 and R-22 at different mass qualities, different pipe diameters, and different saturation temperatures. It is shown that the published data can be well bounded for a wide range of mass fluxes, mass qualities, pipe diameters and saturation temperatures. The bounds models are also presented in a dimensionless form as two-phase frictional multiplier (φl and φg) versus Lockhart-Martinelli parameter (X) for different working fluids such as R-12, R-22, air-oil and air-water mixtures.
Turbulent Heat Transfer in Channels With Solid and Porous Baffles
Authors: de Lemos Marcelo J. S. , Santos Nicolau B.
Published: April 2008

Simulations are presented for turbulent flow in a channel containing baffles made with solid and porous materials. The equations of mass continuity, momentum and energy are written for an elementary representative volume yielding a set of equations valid for the entire computational domain. These equations are discretized using the control volume method and the resulting system of algebraic equations is relaxed with the SIMPLE method. The presented numerical results for the friction factor f and for the Nusselt number Nu were compared with available data. Further simulations comparing the effectiveness of the porous material used showed that no advantages are obtained when using low porosity baffles in the turbulent flow regime.
Vibration of Soils and Foundations: Literature Review
Authors: Luo Albert C. J. , Dehghani Mohammad , Hamidzadeh Hamid R.
Published: April 2008

Research on vibration of soils and foundations has yielded several fundamental methods for formulation of interaction problems. This paper is intended to survey the development of the current state-of-practice for design and analysis of dynamically loaded foundations. Extensive studies in this field utilize various linear mathematical models for interaction between foundations and different soil media. The effective analytical, numerical and experimental techniques and their methodologies which are well established for treating problems in dynamic soil-foundation interaction are outlined. Described techniques are categorized based upon formulation procedures and their applications. Some areas are indicated where further research is needed.
Mechanical and Thermal Behavior for Machining Ti-6Al-4V With AlMgB14 and WC-Co Tools
Authors: Deshayes L. , Evans J. L. , Ivester R. , Bhat D. G. , Batzer S. A. , Whitenton E. P.
Published: April 2008

Many tool materials dissolve, diffuse, and/or react with titanium due to the high temperatures at the tool/workpiece interface. Potential next generation tool materials that would improve the machining of titanium and eliminate the contamination of the work piece are being developed. One material, Aluminum Boride (AlMgB14), is the basis of the research presented in this paper. Specimens of the newly developed tool material, AlMgB14 were fabricated into a standard tool geometry. This tool material was compared with a standard WC-Co tool material to machine a Ti-6Al-4V workpiece. During orthogonal cutting, thermal and force measurements were made using both types of tool material. The measurements are compared with finite element simulations. This paper shows higher chip temperatures are obtained with AlMgB14 and this material demonstrates benefits associated with tool thermal conductivity, including improved chip segmentation, smaller cutting and thrust forces. Nevertheless, a weakness of AlMgB14 is its fracture toughness, which needs to be improved for better performance in an industrial environment.
An Enhanced Model for Shape Memory Alloy Actuators With Complex Thermomechanical Loadings
Authors: Kolivand Mohsen , Elahinia Mohammad H.
Published: April 2008

This paper presents an enhanced phenomenological model for shape memory alloy wires. Shape Memory Alloys (SMAs) are a group of materials with unique phase transformation related characteristics. They have been applied in both active and passive ways for actuation, vibration suppression, and sensing. SMA phenomenological models are widely used for engineering applications due to their simplicity and ease of simulation. A phenomenological model normally has two parts: a constitutive model based on free energy analysis and a phase transformation kinetics model based on experimental results. The existing phenomenological models are formulated to qualitatively predict the behavior of SMA systems for simple loadings. In this study, we have shown that there are certain situations in which these models are either not correctly formulated, and therefore are not able, to predict the behavior of SMA wires or the formulation is not straightforward for engineering applications. Such cases mostly happen when the temperature and the stress of the SMA wires change simultaneously. The phenomenological models discrepancy is studied experimentally using a dead-weight that is actuated by a SMA wire. An enhanced formulation is presented along with a modeling methodology for SMA systems with complex thermomechanical loadings.
The Advisor, a Fuzzy Knowledge-Based System for Rapid Instrumentation and Control Using a Taguchi-Based Quality Function: Part II — Implementation
Authors: Tantra Riko , Masada Glenn Y.
Published: April 2008

Part II of this paper describes the implementation of The Advisor in selecting a load motor system for a motor failure design project. Specifically, the Motor Advisor is used to select a load motor, motor driver and motor controller for an accelerated brushless DC motor platform design. The optimal solution from the Motor Advisor is compared with and is shown to be better than equipment previously selected for that application. The ranked solutions show good tradeoffs between application requirements and user preferences as a result of using the new Quality Function described in Part I.
Low Velocity Impact of Spectra®/Carbon Fiber Laminates Under Varied Temperature
Authors: Evensen Todd , Mahinfalah Mohammad , Salehi-Khojin Amin , Nakhaie Jazar G.
Published: April 2008

Impact properties, at varied temperatures, of carbon fiber and Spectra® 1000 combination laminate composites were investigated in this study. The focus of this research was to determine if any improvement in impact properties existed as a result of replacing one and two impact-side layers of carbon fiber with Spectra. Tests were conducted on different samples and sample types to obtain information about absorbed energy and maximum impact force at impact energies between 10J and 25J. Temperature effects were studied by conducting impact tests on similar samples at temperatures varying from −50°C to 125°C. The data collected helps to determine the advantages and disadvantages of replacing carbon fiber with Spectra. Temperature testing results showed that impact properties are dependent on temperature and room temperature testing is not sufficient to fully understand laminate composite properties.
Stream of Variation Based Error Compensation Strategy in Multi-Stage Manufacturing Processes
Authors: Djurdjanovic Dragan , Zhu Jie
Published: April 2008

Linear state space Stream of Variation (SoV) models of error flow in multistation assembly and machining systems have been well studied in the past decade. SoV models were utilized for identification of process-level root causes of manufacturing errors, quantitative characterization of measurements in multistation manufacturing systems, systematic selection of measurement points and features, as well as tolerance allocation and process design. Nevertheless, natural connection of the linear state space form of SoV models with traditional control theory has not been utilized to automatically compensate observed manufacturing errors and thus close the quality control loop. Recent advances in measurement technology and flexible fixtures make such operations possible and in this paper, we propose a method for strategic elimination of root causes of quality problems based on the SoV models of the flow of manufacturing errors. Furthermore, the concept of compensability that quantitatively depicts the capacity of error compensation in a specific system is proposed. Based on this concept analogous to the controllability in the traditional control theory, compensable and non-compensable subspaces of dimensional errors are identified and quantitatively described. Theoretical results have been demonstrated using the SoV model of a real industrial process used for machining of automotive cylinder heads.
Design of a Cold Plate Tester for Accurate Measurement of Thermal Performance
Authors: Lakhkar Nikhil , Iyengar Madhusudan , Ellsworth Michael , Agonafer Dereje
Published: April 2008

With the continuing industry trends towards smaller, faster and higher power devices, thermal management has become an extremely important element in the development of computer products. The primary goal of a good thermal design is to ensure that the chip can function at its rated frequency, while maintaining its junction temperature below the specified limit, to ensure reliable operation. The use of a heat sink or cold plate to manage the external thermal resistance has been well documented in the literature. However, the measurement of thermal performance of today state-of-the-art cold plates is challenging because of the low value of thermal resistance that they offer to heat dissipation. In this paper, the design of a tester apparatus for such high performance cold plates is presented. The expected performance of the tester is modeled numerically for a heat flux of 250 W/cm2, and for a range of footprint areas of 100-400 mm2. The analysis study is supported by a detailed uncertainty analysis that utilizes a Monte Carlo simulation approach. It was observed that the sum of random and repeatable errors could be controlled to within ±7.5% even for a very high performance cold plate with an effective heat transfer coefficient of 200,000 W/m2-K dissipating 250 W/cm2, with assumed errors in other relevant parameters.
A Method for Simulating and Measuring the Concentration of Oxygen by Absorption Laser Spectroscopy
Authors: Mei Anhua , Aung Kendrick
Published: April 2008

It is important for dynamic combustion control to collect the information of gaseous species in combustion systems including their concentrations and distributions. Absorption laser spectroscopy has been an effective tool for detection and measurement of gaseous species found and produced in combustion process. This paper studies the computation model to inverse oxygen concentrations from measurement data based on Beer-Lambert law, Lorentz distribution and HITRAN2004 database. The paper presents a fixed wavelength laser absorption spectroscopy consisting of economical laser sensors. The scheme of experiment was presented for measuring the concentration of gaseous oxygen in a single species and a mixture of Oxygen and Helium separately using a 780 nm laser diode and a 633 nm Helium Neon laser. Experimental data were agreed well with the data in HITRAN2004.
Nonlinear Modeling and Theoretical Development of Tire Nonuniformity Induced Tangential Steering Wheel Vibrations
Authors: Cherian Vinod , Jalili Nader , Haque Imtiaz
Published: April 2008

This paper describes a nonlinear modeling approach for a double wishbone suspension developed to investigate the nonlinear kinematics and dynamics in the closed, spatial kinematic chain configuration of the suspension. This model is linked to a nonlinear rack and pinion steering subsystem model in order to study the steering nibble (steering wheel rotational vibrations). The suspension mechanism is idealized as a four degree-of-freedom model for a power assisted rack and pinion steering system, with suspension members considered as rigid links and the bushings idealized as linear spring-damper elements. A system of relative coordinates is used in the suspension subsystem model to minimize the number of equations that would be necessary due to the large number of geometrical and kinematic constraints. The equations of motion for the analytical subsystem models are derived symbolically using Maple and solved numerically using Matlab. The results of simulation of the model subjected to a virtual Kinematics and Compliance (K&C) test are compared with the results generated by the developed ADAMS model based on the parameters obtained from a vehicle manufacturer subjected to the same virtual test. Based on the results of the virtual K&C tests and quasi static simulation of the ADAMS model and the analytical models of the vehicle suspension subsystem, the kinematics results match ADAMS model very closely.
Experimental Testing and Validation of Tangential Steering Wheel Vibrations Due to Tire Nonuniformity
Authors: Ayglon Virgile , Cherian Vinod , Jalili Nader
Published: April 2008

This paper describes the experimental testing and validation of the analytical models developed in our companion paper (IMECE2005-81581) for the nonlinear kinematics and dynamics of the suspension linked to a nonlinear rack and pinion steering system model. More specifically, the experimental results are used to cross verify the numerical simulations of the nibble using custom built analytical and ADAMS models, described in the companion paper. For this, shop floor based quasi-static Kinematic and Compliance (K&C) and dynamic testing results along with track testing on special purpose track at Michelin are presented. Other results include impulse testing of the steering system, as mounted on the vehicle, as well as shaker testing to verify the results. Road testing is also carried out at speeds close to the vehicle critical speed in order to compare and validate the suspension models using the quasi-static K&C testing. The road testing results demonstrate the variation of forces in the steering system due to tire imbalances, emphasizing the nonlinear effects in the vehicle system modeling as well as the variation of the shimmy phenomenon with vehicle speed and tire imbalance.
A New Hysteresis Model for Piezoelectric Actuators With Application to Precision Trajectory Control
Authors: Bashash Saeid , Jalili Nader
Published: April 2008

Piezoelectric actuators with their sub-nanometer resolution and fast frequency response are becoming increasingly important in today’s micro-and nano-positioning technology. Along this line, this paper undertakes the development of a nonlinear modeling, system identification and control framework for piezoelectric actuators used in such positioning systems. More specifically, a general nonlinear modeling framework for a single piezoelectric actuator combined with a novel method for describing its hysteretic nonlinearity is proposed. For the actuator generated force, a polynomial form of the nonlinearity is assumed, and the time-varying history-dependent parameters of this polynomial are identified through the observed hysteretic characteristics of the actuator. Experimental results demonstrates the validity of the proposed the modeling and identification framework for an in-house high resolution piezoelectric-based stager with capacitive position sensor. Utilizing Lyapunov method and the sliding mode control strategy, the control force acting on the actuator is then designed such that the high frequency tracking control and the asymptotic stability of the system are attained. Simulation results indicate that controller suppresses the high frequency tracking error significantly, noticeably improving the tracking performance.
Passive Nonlinear Vibrations of a Directly Excited Nanotube-Reinforced Composite Cantilevered Beam
Authors: Mahmoodi S. N. , Jalili Nader , Khadem S. E.
Published: April 2008

This paper undertakes the passive nonlinear vibration analysis of a directly excited composite cantilever beam modeled as an inextensible Euler-Bernoulli beam. The composite beam consists of two elastic layers of high-carbon steel sandwiched together through a viscoelastic layer of carbon nanotube (CNT)-epoxy mixture. The resulting viscoelastic damping is modeled as Kelvin-Voigt damping model, with the nonlinearities present due to inextensibility assumption. In order to study the system response characteristics, the method of multiple scales is employed to arrive at the modulation equations and the closed-loop frequency response function. Such analytically-derived frequency response is experimentally verified through harmonic force excitation of samples of CNT-reinforced composite beams. The results demonstrate that increasing the excitation amplitude or decreasing damping ratio can cause a minor decrease in the nonlinear resonance frequency despite the significant increase in the amplitude of vibration due to reduced damping.
A Freshman Design-Build-Launch Experience
Authors: Fisher Cary A.
Published: April 2008

This paper will describe an “Introduction to Engineering Systems” course taught to ALL freshmen students at the Air Force Academy. Not your normal freshman mechanical engineering course, Engineering 100 (ENGR100) is a web-based, hands-on systems design course where student teams design, analyze, build and fly a rocket-powered, controllable boost-glide “concept demonstrator.” Along the way they learn (in just-in-time fashion) the fundamentals of mechanical, electrical, aeronautical, astronautical, civil and environmental engineering. The course begins with a one-lesson design exercise, followed by a discussion of the “Engineering Method” and how it compares to (and differs from) the scientific method. Next, each team is given a Statement of Work (SOW), requiring them “to design, build, and test a concept demonstrator system...to represent the configuration, launch facilities, and mission profile of a Hypersonic Orbital Global Strike System (HOGSS).” The Statement of Work is somewhat daunting to most students, so we help them proceed as engineers do: break the big problem into smaller, more manageable projects. Students learn a bit about ballistics, drag, and the power of an interactive spreadsheet, before building and launching their model rockets on our parade field to verify their predictions. On-line tutorials help them understand the importance of paying attention to balsa wood grain alignment prior to glider launch day from the field house balcony. They see the importance of servo arm and control rod placement for best mechanical advantage using in-class models and videos. They verify the stability and control of their boost glider design, both on the spreadsheet and in our “homemade” wind tunnel. On launch day they experience the thrill of victory as well as the opportunity for redesign! Each lesson is peppered with both instructional and motivational videos keyed to the daily reading assignment. Class time is used for additional demonstrations, team meetings, reinforcement of the more challenging concepts, and plenty of lab design-build-test-redesign opportunities. Student teams document their progress in a structured “Team Binder,” and present their results in several formal briefings. This course has been taught to over 3000 students the past six semesters with impressive results, validated by various imbedded assessment methods.
Development of a Unique, Passive, Microgravity Vortex Separator
Authors: Ellis M. , Kurwitz C. , Best F.
Published: April 2008

In the microgravity environment experienced by space vehicles, liquid and gas do not naturally separate as on Earth. This behavior presents a problem for two-phase space systems, such as environment conditioning, waste water processing, and power systems. Furthermore, with recent renewed interest in space nuclear power systems, a microgravity Rankine cycle is attractive for thermal to electric energy conversion and would require a phase separation device. Responding to this need, researchers have conceived various methods of producing phase separation in low gravity environments. These separator types have included wicking, elbow, hydrophobic/hydrophilic, vortex, rotary fan separators, and combinations thereof. Each class of separator achieved acceptable performance for particular applications and most performed in some capacity for the space program. However, increased integration of multiphase systems requires a separator design adaptable to a variety of system operating conditions. To this end, researchers at Texas A&M University (TAMU) have developed a Microgravity Vortex Separator (MVS) capable of handling both a wide range of inlet conditions as well as changes in these conditions with a single, passive design. Currently, rotary separators are recognized as the most versatile microgravity separation technology. However, compared with passive designs, rotary separators suffer from higher power consumption, more complicated mechanical design, and higher maintenance requirements than passive separators. Furthermore, research completed over the past decade has shown the MVS more resistant to inlet flow variations and versatile in application. Most investigations were conducted as part of system integration experiments including, among others, propellant transfer, waste water processing, and fuel cell systems. Testing involved determination of hydrodynamic conditions relating to vortex stability, inlet quality effects, accumulation volume potential, and dynamic volume monitoring. In most cases, a 1.2 liter separator was found to accommodate system flow conditions. This size produced reliable phase separation for liquid flow rates from 1.8 to 9.8 liters per minute, for gas flow rates of 0.5 to 180 standard liters per minute, over the full range of quality, and with fluid inventory changes up to 0.35 liters. Moreover, an acoustic sensor, integrated into the wall of the separation chamber, allows liquid film thickness monitoring with an accuracy of 0.1 inches. Currently, application of the MVS is being extended to cabin air dehumidification and a Rankine power cycle system. Both of these projects will allow further development of the TAMU separator.
Machine Learning and Model Based Reasoning for Prognostics of Complex Systems
Authors: Marko Kenneth
Published: April 2008

Model based reasoning (MBR) has been shown to be an effective means of providing condition based maintenance for many high-value assets for which accurate first principle models have been developed. Yet, many low-cost complex computer controlled systems are mass-produced without the concurrent provision of precise physics based models. We wish to utilize new developments in machine learning coupled with model based reasoning methods to address this deficiency. In particular, we shall demonstrate that for an important class of these systems, the extremely large number of mass produced, complex engine systems which power vehicles and small power generation plants, effective means of providing MBR for condition based maintenance exists. It will be recognized that the methodology also has much broader applicability. We will show that a class of dynamic neural networks can be used to provide high-fidelity models of these complex systems that permit an analysis of differences between predicted normal behavior and actual plant behavior to be analyzed to detect deviations from nominal behavior which will be shown to be valuable in estimating time-to-failure for such systems. The realization of this capability is dependent upon the development of extremely efficient and powerful training algorithms for these dynamics neural networks. While many simple training schemes have been in use for many years, they generally fail to provide the needed model accuracy when they are applied to training the relatively “large” multi-layered dynamic networks that are needed to precisely mimic plant behavior over all operating conditions. Our approach has several advantages over these simpler, but less effective methods. Three major improvements are the rate at which learning proceeds, the provision of a means to optimize the learning rate through-out the process, and the dramatic improvements observed in learning in the final stages of training when the error feedback from training examples are extremely small and the associated error covariance matrices almost vanish. We shall demonstrate with data drawn from production vehicles, that for several important problems in analyzing system performance in these vehicles, sufficient model fidelity can be attained to meet the requirements on detection efficiency, false alarm immunity and alarm response time which are required for effective diagnostics and prognostics. Finally we shall discuss the manner in which the deviations are analyzed to not only identify that a failure has been detected but also the means by which the probable root cause may be isolated.
Theoretical and Experimental Performance of a High Frequency Micropump
Authors: Astle Aaron , Bernal Luis P. , Kim Hanseup , Najafi Khalil , Washabaugh Peter D.
Published: April 2008

This paper details theoretical analyses and experimental characterization of high-frequency multi-stage micro pumps. The MEMS-fabricated micro pumps have been developed for use in a highly-integrated chemical monitoring system under development at the University of Michigan’s Wireless Integrated Micro-Systems center. Tests are reported on a 20x meso-scale 2-stage pump developed to validate the theoretical analyses. Detailed comparisons of the pump performance and unsteady pressure traces show that the theoretical analyses capture the main features of the flow in the pump. A MEMS-fabricated device has been developed and tested. The use of theoretical analyses for the design of the pump is described. This device produces A maximum flow of 1.1 ccm and a maximum pressure of 879 Pa.
Parametric Sensitivity Analysis and Model Tuning Applied to Vapor Compression Systems
Authors: Keir Michael C. , Rasmussen Bryan P. , Alleyne Andrew G.
Published: April 2008

This paper presents a parameter sensitivity analysis for a low-order control-oriented dynamic model of a subcritical vapor compression system. The results are used to tune immeasurable model parameters, account for the unmodeled system dynamics, and are applied to fault detection residual design. The models are validated against data taken from an experimental test stand, and the sensitivity based model tuning is shown to improve the model accuracy while providing enhanced physical insight into system dynamics.
Numerical Analysis of Convective Boiling Heat Transfer of a Horizontal Tube Immersed in a Saturated Liquid With an Upward Velocity
Authors: Yan Xiaojun T. , Deng Haibo , Rabiei Khalil
Published: April 2008

Numerical simulation of boiling heat transfer of a horizontal tube is important. It can provide insight into the modeling of boiling phenomena and help select the right models to predict heat transfer for industrial applications such as in kettle reboilers. In this study, heat transfer characteristics of convective boiling on the outside of a horizontal tube immersed in a large saturated liquid with upward velocity is studied numerically by using finite volume method with the mixture model in multiphase flow. Turbulence is modeled by the standard κ – ε model in mixture of multiphase. For different heat fluxes with different upward flow velocities, the local angular distribution of heat transfer coefficient and void fraction around the tube are presented. The results are compared with relevant experimental data.
Geometrical Effects of Cabinet Size and Aspect Ratio on Heat and Mass Transfer During Open Door Conditions
Authors: Terrell W.
Published: April 2008

The goal of this paper is to examine the effects of size and aspect ratio (H/L) of open cavities on heat and mass transfer during open door conditions of refrigerator cabinets. An experimental investigation was conducted using test cavities constructed from foam board insulation and interior covered with aluminum plates acting as calorimeters. Various size cavities with heights of 15.24 cm, 30.48 cm, and 45.72 cm along with aspect ratios of 0.5, 1.0, and 2.0 were tested. Cavities were heated to an initial temperature of 50°C, 60°C, 70°C, and 80°C before being exposed to the ambient air. In addition, tests were conducted in which the cavities were cooled before being exposed to the ambient. The relative humidity was varied from 60% to 75% and initial temperatures varied from 5°C, 1°C, and −5°C. The cavity mass fluxes were measured to validate the heat/mass transfer analogy for the tests. Experimental results were also presented for Rayleigh numbers from 5.88 × 106 to 2.21 × 108 with Nusselt numbers ranging from 15.48 to 53.51. The Nusselt numbers for cavities with an aspect ratio of one and two were in good agreement with each other. The Nusselt numbers for the cavity with an aspect ratio of 0.5 were slightly lower than the other cavities at given Rayleigh values.
Design of a Piezoresistive Surface Micromachined Three-Axis Force Transducer for Microassembly
Authors: Roman Gustavo A. , Bronson Jessica R. , Wiens Gloria J. , Jones James F. , Allen James J.
Published: April 2008

One of the challenges facing microrobotic manufacturing is the ability to sense interactions for force-guided assembly of small devices. There is a need for a force transducer with the ability to sense forces in multiple degrees-of-freedom in the mN range with resolution on the order of 10 μN for microassembly applications. This paper presents theoretical studies for developing a surface micromachined piezoresistive force transducer that can measure normal force in the z-direction and moments about the x and y-axes. The devices proposed here are based on a compliant platform design with integrated piezoresistive sensing elements fabricated in a modified SUMMiT process. Various configurations and sensor element layouts are explored to determine the relationship of the applied forces and moments experienced during assembly and the corresponding strain. Structural and finite element analysis is used to determine the elastic response of the device and establish the best locations and orientations of the sensing elements to effectively utilize the piezoresistive effect of the polysilicon sensors. Initial experiments show the polysilicon piezoresistors to have a gauge factor of approximately 25. The expected sensitivities for these devices are presented.
Selection of Operating Modes of a Multi-Functional Hydraulic Device
Authors: Shenouda Amir , Book Wayne J.
Published: April 2008

The field of earth moving equipment is experiencing a transformation due to the introduction of more electronic control capability and advanced control concepts. Conventional hydraulic control systems are controlled by proportional directional spool valve. The construction of the spool valve is such that a given position of the spool determines the flow in and the flow out restriction sizes. Thus, metering in and metering out are dependent or coupled. A certain restriction size on the inlet corresponds to a certain restriction size on the outlet. Therefore, we have one degree of freedom. It can provide for good motion control but it cannot achieve energy saving potential at the same time. In this paper, the concept of ‘independent meter in / meter out’ will be emphasized. Decoupling of meter in from meter out provides for more controllability and potential for energy saving in overrunning load cases when compared with a conventional spool valve controlled hydraulic system. A four-valve configuration controlling a hydraulic cylinder will be stressed. The four-valve configuration can operate in several modes because each of the four valves is controlled separately from the others. Five of these metering modes will be pointed out; two conventional modes and three regenerative modes. An industry system supplier has introduced a novel distributed independent metering in/meter out hydraulic system with actuator force feedback. This control system is going to presented in brief. The distributed, actuator mounted implementation of this system maximizes the efficiency of the regeneration flow by minimizing the line losses associated with the recirculating fluid This control system can be used to control a multi-functional hydraulic device, e.g. excavators, tractor loader backhoes, etc... An experiment was done where a typical dig cycle was performed by a tractor loader backhoe equipped with this new technology. The data recorded from this experiment is used to perform an off-line optimization of metering modes selection for each function during the cycle. this off-line optimization can be used to maximize machine productivity or machine efficiency or a weighted combination of both. A general objective function will be presented and results will be given for maximizing machine productivity. Finally conclusions and future work suggestions are presented.