bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing the Effect of 319 Aluminum Microstructure on Machinability: Part 2 — Model Validation
Authors: Hu Xuefei , Sutherland John W. , Boileau James M.
Published: April 2008

In Part 1 of this paper, a machining force model was developed based on an enhanced version of Zheng’s Continuum Mechanics model that incorporates microstructural effects. Machining experiments identified Secondary Dendrite Arm Spacing (SDAS) as a significant microstructure feature of 319 aluminum in terms of machinability. A new material constitutive relationship that incorporates SDAS microstructure effects on the flow stress was proposed. In this part of the paper, disk turning tests are performed to simulate the orthogonal cutting process. The cutting forces obtained from some of these tests are used in concert with an inverse form of the continuum mechanics machining model to estimate the parameters in the material constitutive equation. The enhanced continuum mechanics orthogonal cutting model is then applied to predict cutting forces when machining Al319. Comparison of the model predicted and experimentally acquired cutting forces is demonstrated to show good agreement.
Study on Correlation of Key Points Temperature of Membrane Water Wall
Authors: Zhang Zhi-Zheng , Sun Bao-Min , Xu Hong , Guo Yong-Hong
Published: April 2008

To monitor the severe points of boiler water wall on-line, a method that is suitable for membrane water wall tube is presented in this paper based on the results from numerical simulation to the temperature fields of the membrane water wall tube. The section temperature fields of the membrane water wall tube can be obtained through numerical simulation under various work conditions in advance. On basis of the temperature fields, the formulations of temperature difference of the three key points on back side and convection coefficient inside and heat flux outside can be set up. The same work can be done to the two severe points on fire side. After then the correlation formulations about the three key points and the two severe points can be obtained. Using these formulations, the temperature of two severe points can be calculated promptly by monitoring the three key points’ temperature.
An Approach to Multidimensional Equivalent Fatigue Loadings
Authors: Genet Gwenae¨lle , Johannesson Pa¨r , Gualandris David , de Mare´ Jacques , Nguyen-Tajan T. Mac-Lan
Published: April 2008

In the automotive industry, temporal, financial and human constraints require continuous improvements in the design process of new vehicles, by delivering relevant specifications and providing reliability and robustness in design. In order to analyze factors like behaviors of drivers and types of roads and guarantee the reliability of car components, measurements of forces from wheels are stored when the vehicle is tested on tracks and used by customers. The measurements represent the time history of multi-dimensional forces on the four wheels in the longitudinal, vertical and transversal directions. They are applied on structures (suspensions or motoring for instance) during the design life of the vehicles. The context of this paper is the fatigue analysis of multi-input loadings. The study will be focused on random and possibly correlated multi-input processes, representing multidimensional forces. The goal of this paper is to present an approach to generate simple multi-input loadings equivalent to measurements in terms of damage. The simple loadings have to be equivalent for any arbitrary structure, satisfying the reliability requirements imposed by the car manufacturer.
Uncertainty Considerations for Ballistic Limit Equations for Aerospace Structural Systems
Authors: Schonberg William P. , Evans Hilary J. , Williamsen Joel E. , Boyer Roger L. , Nakayama Glen S.
Published: April 2008

The overall risk for any spacecraft system is typically determined using a Probabilistic Risk Assessment (PRA). A PRA determines the overall risk associated with a particular mission by factoring in all known risks to the spacecraft during its mission. The threat to mission and human life posed by the mircro-meteoroid and orbital debris (MMOD) environment is one of the risks. NASA uses the BUMPER II program to provide point estimate predictions of MMOD risk for the Space Shuttle and the ISS. However, BUMPER II does not provide uncertainty bounds or confidence intervals for its predictions. In this paper, we present possible approaches through which uncertainty bounds can be developed for the various damage prediction and ballistic limit equations encoded within the Shuttle and Station versions of BUMPER II.
A Stochastic Constitutive Model and Multi-Field Approach for Modeling the Dynamic Response of Cellular Materials
Authors: Schraad Mark W.
Published: April 2008

A multi-field approach is developed for simulating the dynamic response of cellular materials. A stochastic constitutive model is incorporated for representing the stress-strain behavior of cellular solids, however, a description of the coupled response of the permeating fluids also is included. This new approach is used to study the influence of various permeating fluids and the effects of aperture size and loading rate on the continuum-scale response of such systems. Results demonstrate that the permeating fluid can play a significant role in the response of cellular materials, contributing to the load-carrying capacity and affecting rate dependence and signal propagation speeds. Furthermore, the results point to the usefulness of the multi-field formulation and provide evidence to suggest that any modeling approach developed for cellular materials provide a proper accounting of the pressure evolution and flow behavior of the fluids present in these material systems.
Experimental Investigation of the Structural Scattering Due to Impedance Discontinuities on a Cylindrical Shell
Authors: Glotzbecker Ryan J. , Hambric Stephen A. , Pollack Martin L.
Published: April 2008

Experimental, numerical, and analytical work has shown that the response of a shell to a distributed force wave possesses unique characteristics which are dependent on the nature of structure attached to the shell. Specific characteristics which influence the response are the distribution of the discontinuities around the circumference (periodic/a-periodic), the impedance of the discontinuities relative to that of the shell, and the type of impedance (mass or stiffness). An experimental investigation into the harmonic scattering behavior of a shell due to mass discontinuities is presented in this paper. Knowledge of the key structural characteristics which influence scattering and their behavior will allow for a diagnostic tool when assessing the structural response of more complex cylindrical structures. Changes in structural response on a mode number basis as a result of the change in mass discontinuities are explored. Spatial Fourier analysis of both the input force and output response is used to provide a measure of the structural response matrix on a mode-by-mode basis. A distributed input force is simulated by applying forces around the circumference of the shell, then subsequently weighting the phase and amplitude of the measured transfer function according to the input force wave desired. This technique was applied to a shell in its unmodified condition, with periodic masses attached, and with aperiodic masses attached. Test results indicate that some harmonic scattering is present in the clean structure (no attached mass), likely due to non-ideal boundary conditions and the weld seam of the pipe used. Test results for the structure with periodically distributed masses indicate that response harmonics equal to the sum of input the harmonic number and an integer multiple of the number of discontinuities were excited. The structure with a-periodically distributed masses appears to scatter energy from the force harmonic into all response harmonics.
Pressure Measurement and Pattern Recognition by Using Neural Networks
Authors: Piroozan Parham
Published: April 2008

This paper describes an intelligent control system that uses electro-optics and neural networks to control the flow of air over a flexible wall. In this investigation a pressure sensor which was part of the wall of the wind tunnel and an optical apparatus were used to produce moire´ fringes. A back propagation neural network was used to analyze the fringe patterns and to classify the pressures into four levels. A second neural network was used to recognize the pressure patterns and to provide the input to a control system that was capable of modifying the shape of the flexible wall in order to preserve the stability of the flow. The flexible wall was part of the wall of the wind tunnel and was installed in the upstream of the flow. It was made of silicone rubber and had an area of 76 mm by 76 mm. There were 15 rows of actuators installed under the flexible wall which were used to change the shape of the wall. In the downstream of the flow was an optical pressure sensor which had the same dimensions as the flexible wall and consisted of a 15 × 15 array of small diaphragms. These diaphragms responded to the pressure fluctuations in the boundary layer flow and were the source of the signals for the optical system. A CCD camera viewed the pressure sensor through an optical apparatus which produced moire´ fringes. A back propagation neural network analyzed the fringe patterns and classified the pressures into four levels. The classified pressures which was a 15 × 15 array of numbers ranging from 1 to 4 was the input to a second back propagation neural network which was used to recognize the pressure patterns. The output from the back propagation neural network used for pattern recognition provided the input to a control system that changed the shape of the flexible wall. This paper presents the experimental results as well as the computer simulations which were created for this project. This includes the complete process of creating the slope fringes, classifying the pressures into four levels, recognizing the wall pressure patterns and generating the output signals to the actuator for changing the shape of the flexible wall.
Effects of Electrical Resistance of the Gas Diffusion Layer of a PEM Fuel Cell
Authors: Zhou Tianhong , Liu Hongtan
Published: April 2008

A three-dimensional computational model of polymer electrolyte fuel cell (PEMFC) was employed to investigate the effects of electron transport through the gas diffusion layer (GDL) and catalyst layer. The electron transport equation was added to our previously established 3D model. Using reasonable electrical conductivities for the GDL and catalyst layer, especially the different values for the in-plane and through-plane conductivities for the GDL, it was found that the effect of the electronic resistance of GDL is not as significant as previous researches suggested. The previously overestimated effect was mainly caused by assuming the GDL’s in-plane conductivity to be the same as through-plane conductivity, which can have an order of magnitude difference. Comparing the magnitude of ohmic loss from the electron current to that of the proton current, it can also be concluded that the ohmic heating from the electron current is negligible.
New Approach for Engineering Design of Bolted Joints Using Over-Elastic Behaviour
Authors: Friedrich C. , Panthel J. , Bohlender T.
Published: April 2008

The behavior of bolted joints in component systems with relatively small fastening systems, critical materials or with high loading level often shows significant yielding effects with reduction of preload. Thus, poor reliability or even failures are possible. This problem requires an adaptation of the established analytical engineering design methods. A new approach with consideration of over-elastic behavior and preload history is proposed. Examples refer to magnesium components, contact pressure and tightening with angular control.
Suppression of Base Vibrations and Tracking of the Tip of an Inverted Pendulum Using Sliding Mode Control and Quantitative Feedback Theory
Authors: Rajapakse Nuraj I. , Happawana Gemunu S. , Hurmuzlu Yildrim
Published: April 2008

This paper presents a robust control method, combining Sliding Mode Control (SMC) and Quantitative Feedback Theory (QFT) to track the tip of an inverted pendulum, subject to base excitation. A Nonlinear inverted pendulum (IP) model is considered to analyze tracking control characteristics through computer simulation in order to demonstrate the effectiveness of the proposed control methodology. The sliding mode control is used to track the trajectory of the tip of the inverted pendulum. However, when the system enters into sliding regime, chattering occurs due to switching delays as well as base vibrations. The chattering is eliminated with the introduction of quantitative feedback theory inside the boundary layer to ensure smooth tracking. Problems with noise amplification, resonances, presence of uncertainties and unmodeled high frequency dynamics can largely be avoided with the use of QFT over other optimization methods. In addition, the QFT design methodology guides design evolution rather than replacing human intervention as would appear to be the case in some control synthesis methodologies.
Chraracterization of a Pulsed Catalytic Micro-Combustor
Authors: Green Darren V. , Scovill David M. , Santavicca Domenic A. , Sharp Kendra V.
Published: April 2008

Experiments have been conducted to determine the effect of operating conditions and design parameters on the performance of a pulsed catalytic micro-combustor. The micro-combustor test rig was designed to simulate the combustor in a prototype version of a solid-piston micro-engine. The performance parameters of interest were the difference between the minimum and maximum catalyst tube temperature and the efficiency with which the chemical energy of the fuel is converted to mechanical work, as defined by the overall system efficiency. The change in the catalyst tube temperature, which is a measure of the mechanical work produced by the expansion of the catalyst tube, was found to decrease with increasing frequency and to increase with increasing duty cycle, velocity, equivalence ratio and combustor diameter. While the overall system efficiency was found to decrease with increasing frequency, duty cycle, velocity, equivalence ratio and combustor diameter. Therefore there is a trade-off between increasing the power output and the efficiency with which that power is produced. The main factor limiting the overall system efficiency was found to be the thermal-to-mechanical efficiency. It was shown that the overall system efficiency can be increased by optimizing the catalyst tube dimensions and by using a material with a larger coefficient of thermal expansion and/or modulus of elasticity. The information obtained from this study will be used to design a new version of the pulsed catalytic micro-combustor with improved power output and overall system efficiency.
Frequency Based Optimal Input Signal Determination for ARX Parameter Estimation of Constraint Systems
Authors: Thumati Balaje T. , Schoen Marco P.
Published: April 2008

Modern parametric based eigensystem realization algorithms (ERA) used in system identification algorithms depend heavily on the quality of the estimated parameters. Generally, parameters are estimated experimentally by exciting all the modes of the system. The generated input/output data is processed using least-squares or maximum likelihood algorithms to fit the parameters of the assumed model to the gathered data. Since the locations of the system modes are not known at the beginning of the system identification experiment, band-limited white noise signals are used as the input. Input design or experimental design for system identification addresses the input signal computation for optimum parameter estimation. Constraint systems, such as commonly found in biomedical engineering applications, represent a particular challenge to the input design algorithm. This paper presents a novel approach that induces learning into the input design computation and allows for considerations of the given constraints of the system. In particular, the proposed algorithm adapts to the information gathered during the first step of the identification experiment and uses this gained information to form a new input that targets the system modes. The input signal starts with a band-limited white noise and based on the response uses the frequency information contained in the preliminary estimated ARX model to shape the new input signal. This new input is computed such that more energy is directed towards the system modes. Since the objective is to accurately estimate the ARX model parameters and therefore the system model, the preliminary estimated ARX parameters posses some uncertainty. The optimization of the new input signal is accomplished using a simple Genetic Algorithm. Simulation results indicate the proposed piecewise adaptive input design algorithm performs well compared to the general white noise based estimation results
Thermodynamic Analysis of a Novel Process With Integrated CO2 Capture for the Production of Electric Power and Hydrogen
Authors: Tsatsaronis George , Kapanke Kerstin
Published: April 2008

This paper presents a detailed description and thermodynamic analysis of a novel process generating electric energy and hydrogen, i. e. two important energy products for the future. Coal and high-temperature heat are used as input energy to the process. The process is a true “zero emission process” because (a) no NOX is formed during coal combustion with sulfuric acid, and (b) the combustion products SO2 and CO2 are removed as compressed liquids from the overall process. The commercial process simulator Aspen Plus was used for the thermodynamic modeling of this process. Detailed results of the simulation are presented. The overall process is characterized by very high energetic and exergetic efficiencies in comparison with other energy conversion systems in which electric power or hydrogen are generated using the same energy inputs. The influence of important process parameters, e.g. the concentration of the sulfuric acid solution on the overall efficiency is discussed. The evaluation of the thermodynamic performance of the process, which is based on a detailed exergetic analysis, represents the first step in a comprehensive evaluation of this concept to be conducted in the future.
Droplet Heating in a Direct-Contact Heat Exchanger: Effect of Electric Field
Authors: Subramanian Rajkumar , Jog Milind A.
Published: April 2008

Heat transfer between two immiscible fluids in a direct contact heat exchanger can be enhanced by the application of an electric field. In this paper, we have numerically modeled heat transfer to a spherical droplet translating in an immiscible medium with an applied electric field. The electric field induces circulatory motion inside and outside the droplet that results in increase in the rate of heat transport. The governing equations for both phases are solved simultaneously by a finite volume method. The external heat transfer problem is considered where the bulk of the resistance is assumed to be in the continuous phase. Effects of electric field strength and translational Reynolds number are investigated.
Design and Evaluation of a Robust Compliant Grasper Using Shape Deposition Manufacturing
Authors: Dollar Aaron M. , Howe Robert D.
Published: April 2008

Robustness is a limiting factor in experimental development of multifingered robot hands: the expense and fragility of these hands precludes casual experimentation, restricting the type of experimental tasks that can be reasonably attempted and slowing implementation due to the need for careful validation of programs. In this paper, we describe the design, fabrication, and evaluation of a novel compliant robotic grasper and demonstrate that polymer-based Shape Deposition Manufacturing allows for the construction of fingers with the functionality of conventional metal prototypes but with robustness properties that allow for uncertainty in object location and large impact forces.
Analysis of Flow Fields in Foaming Die Using Finite Element Method
Authors: Wang Jian-Kang , Huang Han-Xiong
Published: April 2008

The morphology and properties of the extruded polymeric foams are affected by the geometry of extrusion die. In this paper, the flow in the slit die was simulated using POLYFLOW software package to predict the pressure distribution and residence time. Then the pressure drop rate in the die was calculated. The results for seven dies with different length (L) and gap (H) of the straight section were compared. The effects of the L and H on the nucleation position were analyzed. Based on the critical foaming pressure (Pf), the minimum length and maximum gap providing required pressure drop were determined under a constant gap and a constant length, respectively.
Nonlinear Dynamics of Electrokinetic Instabilities
Authors: Posner Jonathan D. , Santiago Juan G.
Published: April 2008

Electrokinetic instabilities are generated by a coupling of electric fields and ionic conductivity gradients. This coupling results in an electric body force in the bulk liquid that can generate temporal, convective, and absolute flow instabilities. In this work, we perform a parametric experimental study of convective instabilities in cross-shaped microchannels using epifluorescence microscopy and high speed digital imaging. We report temporal power spectra and spatiotemporal maps as a function of the applied field. The spectral analyses reveal that disturbances induced by electrokinetic instability are purely sinuous at the onset of instability and exhibit higher-order harmonics, frequency bifurcations, and continuous power spectra with increasing electric Rayleigh number. Electrokinetic instabilities (EKI) in cross-shaped channels are relevant to injections for field amplified sample stacking, electrokinetic flows at the intersections in multi-dimensional assay devices, and systems with indeterminate sample chemistry.
Development of Crack Depth Indicator for Deep Surface Crack
Authors: Hayakawa Manabu , Hamada Seiichi , Takeo Fumio , Saka Masumi
Published: April 2008

Crack depth indicator using a direct current potential drop technique has been generally applied to the nondestructive inspection in the thermal power plants such as steam pipe and turbine casing. In this paper, the authors presented practical studies concerning the development of the advanced crack depth indicator for the deep surface crack. The authors have conducted experimental measurements using the customary crack depth indicator inspecting the fatigue pre-cracked plate specimens of some materials. The results showed that the crack depth indicator was effective to inspect the surface shallow crack, however, it was hardly applied to the deep crack. And the sensor of this equipment was found to be difficult to apply some practical conditions such as contact surfaces and mechanical designs of inspected structures. To get over the restrictions, the authors have developed a new type of crack depth indicator and sensor. The authors have conducted additional experimental measurements applying this equipment using some pre-cracked specimens such as plates and structural components of some materials.
Triply Coupled Vibration Band Gaps in Periodic Thin-Walled Open Cross Section Beams
Authors: Yu Dianlong , Liu Yaozong , Qiu Jing , Wang Gang , Wen Jihong
Published: April 2008

Triply coupled vibration through periodic thin-walled open cross section nonsymmetrical beams composed of two kinds of material is studied in this paper. Based on the triply coupled vibration equation, plane wave expansion method for the thin-walled beams is provided. If the filling fraction keeps constant, the lattice is one of the factors that affect the normalized gap width. If the lattice and filling fraction keep constant, the Young’s modulus contrast plays a fundamental role for the band gap width, but not density contrast. Finally, the frequency response of a finite periodic binary beam is simulated with finite element method, which provides an attenuation of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.
Repowering of Fossil Fuel Power Plants and Reversible Carbonation/Calcination Cycle for CO2 Abatement
Authors: Escosa Jesu´s M. , Cortes Cristo´bal , Romeo Luis M.
Published: April 2008

Fossil fuel power plants account for about a third of global carbon dioxide emissions. Coal is the major power-generation fuel, being used twice as extensively as natural gas (IEA, 2003). Moreover, on a global scale, coal demand is expected to double over the period to 2030; IEA estimates that 4500 GWe of new installed power will be required. Coal is expected to provide 40% of this figure. It is thus obvious that coal power plants must be operative to provide such amount of energy in the short term, at the same time reducing their CO2 emissions in a feasible manner and increasing their efficiency and capacity. However, the main technologies currently considered to effect CO2 capture, both post-and pre-combustion, introduce a great economic penalty and largely reduce the capacity and efficiency. One of these technologies involves the separation of CO2 from high temperature flue gases using the reversible carbonation reaction of CaO and the calcination of CaCO3. The process is able to simultaneously capture sulfur dioxide. The major disadvantage of this well-known concept is the great amount of energy consumption in the calcinator and auxiliary equipment. This paper proposes a new, feasible approach to supply this energy which leads to an optimal integration of the process within a conventional coal power plant. Calcination is accomplished in a kiln fired by natural gas, whereas a gas turbine is used to supply all the auxiliary power. Flue gases from the kiln and the gas turbine can substitute a significant part of the heat duty of the steam cycle heaters, thus accomplishing feed water repowering of the steam turbine. This novel CO2-capture cycle is proposed to be integrated with aging coal-fired power plants. The paper shows that an optimal integration of both elements represents one of the best methods to simultaneously achieve: a) an increase of specific generating capacity in a very short period of time, b) a significant abatement of CO2 emissions, and c) an increase of plant efficiency in a cost-effective way.
Nonlinear Open Loop Optimal Tracking Using Magnetostrictive Transducers
Authors: Oates William S. , Smith Ralph C.
Published: April 2008

The design of high performance smart material devices requires control laws that can achieve stringent performance criteria required in many industrial, automotive, aerospace and biomedical applications. Moderate to high field inputs are often required which introduces nonlinear, hysteretic constitutive behavior. This often cannot be effectively compensated using linear control theory. In the present work, a nonlinear optimal control methodology is developed for tracking a reference trajectory when nonlinear, hysteretic constitutive behavior is significant. For brevity, we focus on open loop control for regimes when disturbances are minimal. The nonlinear control design is investigated on magnetostrictive rod-type actuators by implementing a homogenized energy model. Significant emphasis is place on material behavior at multiple length scales to produce an accurate and efficient model to compensate for nonlinear, hysteretic magnetostrictive constitutive behavior.
Investigation of Stability of a Suspension of Motile Microorganisms Subjected to a High-Frequency Vibration
Authors: Kuznetsov A. V.
Published: April 2008

This paper investigates the effect of vertical vibration on the stability of a dilute suspension of negatively geotactic microorganisms in a fluid layer of finite depth. The case of high-frequency vibration is considered. Solutions of governing equations are decomposed into two components: one which varies slowly with time and a second which varies rapidly with time. An averaging method is utilized to derive the equations describing the mean flow. Linear stability analysis is used to investigate stability of the obtained averaged equations.
Heat Transfer in Laser Sintering of Thick-Film Microelectronics
Authors: Kinzel Edward C. , Xu Xianfan , Sigmarsson Hjalti H. , Chappell William J.
Published: April 2008

This paper investigates fabrication of functional thick-film components using Selective Laser Sintering (SLS). We demonstrated that SLS has exciting potentials for thick-film metallization of low-temperature substrates. The DC conductivity of laser sintered components is measured for a range of laser scan speeds and powers. The quality of metallization at microwave frequencies is evaluated by comparing the measured Q to simulations. The effects of processing parameters on the quality of components are investigated through a heat transfer analysis of the laser sintering process. Optimum properties of the fabricated components are obtained when proper thermal conditions are achieved during laser heating.
Reliability Objects Model: A Knowledge Model of System Design for Reliability
Authors: Kim Injoong , Sitaraman Suresh K. , Peak Russell S.
Published: April 2008

Designing complex systems that satisfy a target reliability is difficult because of complex assembly structures and logical connections, numerous components and associated failure modes, limited reliability data or prediction models, and multi-disciplinary nature. To overcome these difficulties and to design complex systems in a systematic way, this research aims to develop a knowledge model of system design for reliability, called Reliability Object Model. This knowledge model contains a) a new failure analysis structure, b) reliability metrics that represent random failures and wearout failures, c) algorithms that allocate, predict, and assess reliability using the failure analysis structure, d) rules for design changes. The use of Reliability Object Model is demonstrated by prototype reliability tools and simplified electronic systems.
Functional Interface-Based Assembly Modeling
Authors: Stoddard James R. , Law Marvin
Published: April 2008

Current CAD system approaches to assembly representation do not support the full range of needs for an assembly model. They cannot account for the natural manufacturing and assembly variability that occurs in the assembled interfaces. The current solvers work well for idealized assembly design behaviors at nominal conditions, but in order to make accurate predictions about assembly performance and product quality the variability of the assembled interfaces must be comprehended in the assembly model. This paper will outline two key issues to support a robust approach to assembly modeling based on characterizing the true mating surface contact between parts in the assembly. These assembly interface definitions are adaptable enough to achieve an exact constraint design to ensure a stable analysis. These approaches are based in kinematic theory and support the efficient solution of the assembly constraints in the presence of geometric variation. An example of this approach within the context of a tolerance analysis application will be presented.
Biocompatible Fluids for Use in Micro Total Analysis Systems
Authors: King Colin , Walsh Edmond , Grimes Ronan , Gonzalez Asensio
Published: April 2008

The trend in micro total analysis systems is favouring the segmented flow approach as it has the potential to reduce contamination issues and allow for a greater quantity of samples to be processed in any given time frame. With this trend comes the need for biocompatible fluids to separate the bio-samples. To date a number of authors have cited different fluids for this purpose, some noting good results and some noting total inhibition due to the segmenting fluid. This paper aims to demonstrate the extent of reduced efficiency for a number of potential segmenting fluids. A number of PCR samples are thermally cycled in a commercial PCR machine after having been in contact with a variety of potential segmenting fluids. The resulting efficiencies and crossing thresholds are then compared to determine the effects on the bio-samples. This paper details the first quantitative test of PCR compatibility with segmenting fluids. Such work is critical to the development of this technology in an efficient manner. The experimental results of this work are promising for the future of the segmented flow approach to micro-Total Analysis Systems.
Mitigation of Bending Stress and Failure Due to Temperature Differentials in Piping Systems Carrying Multiphase Fluids: Using CFD and FEA
Authors: Diwakar Philip , Mehrotra Vibhor , Richardson Franklin
Published: April 2008

The bending of large pipes due to temperature differentials between the bottom and top of the pipe is a very serious problem. The temperature differentials can either be caused by extremely cold liquids (such as methane or ethylene flowing from a lateral into a flare header) or hot liquids flowing at the bottom of a piping system (such as in a Vacuum transfer line) while the top is exposed to atmospheric conditions. In some cases liquids may be produced by Joule-Thompson cooling of high pressure cold gas as it expands through a safety-relief or emergency depressurization valve. The liquid so formed can accumulate, for example, on the dead leg side of a flare header. The differential expansion can deform the pipe so that it lifts off its supports. It takes a finite amount of time for the heat transfer by conduction to equilibrate the temperature to a more benign level. The initial stresses induced due to large thermal differential may even cause the pipe to crack in the region of the supports and T-joints to the laterals. This phenomenon has been observed in several industries, most predominantly in the petrochemical industry. This paper recounts the use of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) to study this important phenomenon. The liquid flowing from the lateral into the main header pipe is multiphase in the dispersed, stratified, slug or annular flow re´gime. Multiphase flows with heat transfer are analyzed using CFD. The temperatures on the walls of the pipe system are then transferred to the FEA and analyzed for heat transfer and thermal stresses. These stresses are compared to ASME standards to see if they are within allowable limits. This paper also recounts efforts to reduce the bending effect by preventing liquid accumulation on the dead leg side. Other methods that provide better supports for bent piping are studied. Further, methods of equilibrating the temperature faster to prevent the bowing of the pipe are also studied. It is hoped that this presentation will benefit people designing piping networks with varying liquid and vapor traffic by providing a safe environment free of cracks and spills.
Evaluation of a Constitutive Equation for Magnetorheological Fluids in Shear and Elongational Flows
Authors: Ciocanel Constantin , Lipscomb Glenn , Naganathan Nagi G.
Published: April 2008

A microstructural model of the motion of particle pairs in MR fluids is proposed that accounts for both hydrodynamic and magnetic field forces. A fluid constitutive equation is derived from the model that allows prediction of velocity and particle structure fields. Results for simple shear and elongational flows are presented for cases where particle pairs remain in close contact so they are hydrodynamically equivalent to an ellipsoid of aspect ratio two. Additionally, only the magnetic force component normal to the vector connecting the centers of a particle pair affects motion. Shear flow results indicate particle pairs rotate continuously with the flow at low magnetic fields while a steady state is reached at high fields. For elongational flows, when the applied magnetic field is parallel to the elongation direction, particle pairs orient in the field/flow direction. Either orientation is possible when the field is perpendicular to the flow.
Multistage Isoelectric Focusing: A Novel On-Chip Bio-Separation Technique
Authors: Dutta Prashanta , Horiuchi Keisuke , Cui Huanchun , Ivory Cornelius F.
Published: April 2008

This experimental study reports a method to increase the resolving power of isoelectric focusing (IEF) on a polymeric microfluidic chip. Microfluidic chip is formed on poly-di-methyl siloxane (PDMS) using soft lithography and multilayer bonding technique. In this novel bioseparation technique, IEF is staged by first focusing protein species in a straight channel using broad-range ampholytes and then refocusing segments of that first channel into secondary channels that branch out from the first one. Experiments demonstrated that three fluorescent protein species within a segment of pH gradient in the first stage were refocused in the second stage with much higher resolution in a shallower pH gradient. A serially performed two-stage IEF was completed in less than 25 minutes under particularly small electric field strength up to 100 V/cm.
Design and Characterization of a BioMEMS Device for In-Vitro Mechanical Stimulation of Single Adherent Cells
Authors: Panchawagh Hrishikesh V. , Serrell David , Finch Dudley S. , Oreskovic Tammy , Mahajan Roop L.
Published: April 2008

This paper presents development of a BioMEMS device to mechanically stimulate single adherent cells by means of electrostatic actuation. The main components of the proposed device include a platform for cell placement and an electrostatic comb drive actuator to provide in-plane motion. A high frequency actuation method was used to enable actuation in aqueous solutions. Displacements greater than 5μm were measured when the device was actuated with a 1 MHz square wave signal with 10V peak amplitude in DI water. Additionally, this device was successfully actuated in ionic solutions up to 50mM NaCl aqueous solution using frequencies greater than 30 MHz. Significant electrolysis and corrosion of the polysilicon and metal layers was observed when the devices were actuated in saline solutions with peak voltages greater than 15V, thus indicating that there is a limit on the maximum actuation voltage that can be used. No noticeable actuation was observed in phosphate buffer solution (PBS) or cell culture medium even when frequencies as high as 50 MHz were used due to ion migration. Theoretical calculations suggest that frequencies of the order of 100-500 MHz will be required for actuation in cell culture media. Currently we are in the process of building an experimental set-up to allow use of such high frequencies. Initial results for cell plating experiments on the cell stretcher platform and other considerations for device implementation are discussed in the end.
A Methodology to Estimate Degradation and Reliability Based on Artificial Neural Networks
Authors: Susemihl Enrique A. , Xu Shuzhen
Published: April 2008

Failure modes associated with degradation or ageing affect most equipment, and the estimates of failure due to them are particularly important in deciding repair or replacement. A methodology is presented here to relate physical variables with a degradation measure by using artificial neural networks to capture data and experience, and to use this degradation measure to estimate probabilities of failure. This methodology has been applied to transformers to estimate probabilities of failure due to the degradation of paper insulation, and some preliminary results are presented. These results show that the method can provide reasonable estimates.
Solid Modeling: The Cornerstone of Design
Authors: Myszka David
Published: April 2008

For any mechanical design project in an industrial setting, computer-aided design (CAD) functions as the cornerstone. Mechanical CAD systems serves as the focal point during conceptualization, design iterations, finalizing design details drawing creation and manufacturing. In most engineering technology programs, CAD, and solid modeling are offered as required courses. However, those courses often stand as “islands” of information. In the university setting, CAD is poorly integrated into the many design problems presented in courses throughout the curriculum. Frequently, students do not gain the experience of using solid models to drive their designs. Too often, their first experience of this real-world design process is “on the job”. Thus, our students are not fully prepared for industrial practice, which is contrary to the mission of engineering technology programs. This paper will present the results of a study that reviewed utilization of solid modeling throughout many baccalaureate mechanical engineering technology (MET) programs. Further, it will present some of the implementation strategies of solid modeling in upper-level, MET courses at the University of Dayton.
Refinement of a Hypervelocity Gouging Model for the Rocket Sled Test
Authors: Cinnamon John D. , Palazotto Anthony N.
Published: April 2008

In an effort to improve the accuracy of current numerical models of the hypervelocity gouging impact phenomenon at the Holloman Air Force Base High Speed Test Track (HHSTT), several investigations were conducted. First, a metallurgical study of a gouged rail section is summarized that quantifies the nature of the non-equilibrium thermodynamic event. Second, the current CTH model of the sled/rail interaction is scaled mathematically to determine the feasibility of a laboratory experiment to generate gouging. Additionally, the various material contact schemes in CTH are evaluated to determine the most accurate approach in the gouging impact problem. Next, the absence of specific constitutive models for 1080 steel and VascoMax 300 (which are the materials of interest in the HHSTT gouging problem) is addressed with Split Hopkinson Bar characterization. These models are validated by comparison to Taylor Impact Tests conducted on the same materials. Finally, the two coatings used at the HHSTT to mitigate gouging are experimentally compared using the Taylor test. Conclusions are drawn from the experimentation and numerical modeling efforts with regard to the gouging phenomenon.
On the Repetitive Impact Dynamics of One and Two Degree of Freedom Systems
Authors: Yagci Baris , Iannacci Matt , Ozdoganlar Burak , Wickert Jonathan
Published: April 2008

Repetitive collision occurring between structural and machine components is a topic of practical and scientific importance. Some types of machinery are inherently susceptible to impacts because of the small clearances present between adjacent components, thermal expansion, and relative motion as in gear trains. One can observe repetitive impacts in milling machines, shakers and off-shore structures. Energy transfer between components that are subjected to repetitive impacts is a complex phenomenon that often exhibits deceptive and non-intuitive behavior. Even in seemingly simple structures, period-doubling bifurcations, sub-harmonic resonances, and chaotic responses occur. This paper presents detailed experimental data obtained from an impact vibration test stand that was instrumented for displacement, velocity, and impact force measurements. In addition, the apparatus was fabricated in such a way to allow for precise positioning of the impact point, and varying of the gap distance between impacting components. The paper includes companion simulation results obtained from a model for the repetitive impact dynamics of otherwise linear single or multiple degree of freedom discrete structures. Simulation results are presented for the effect of natural frequency placement, model dimension, and gap clearance on the qualitative and quantitative character of the response. Of particular interest is the transition of behavior as the system’s model is augmented from having one to several degrees of freedom.
Design and Validation of a Reduced Test Matrix for the Autoignition of Gas Turbine Fuel Blends
Authors: de Vries Jaap , Petersen Eric L.
Published: April 2008

Changes in fuel composition for both aero-engine as well as power generation applications is a topic of concern since fuel variability can have a great impact on the reliability and performance of the burner design. Autoignition experiments for a wide range of likely fuel blends containing CH4 mixed with combinations of C2H6, C3H8, C4H10, C5H12, and H2 are planned in the authors’ shock-tube laboratory. However, testing every possible fuel blend and interaction is not feasible within a reasonable time and cost. To predict the surface response over the complete mixture domain, a special experimental design has been developed reducing the amount of ‘trials’ needed significantly from 243 to only 41 using the Box-Behnkin factorial design methodology. Kinetics modeling was used to obtain numerical results for this matrix of fuel blends when applied to autoignition at a temperature of 800 K and pressure of 17 atm. A further attempt was made to reduce the 41-test matrix to a 21-test matrix. This was done using special mixture experimental techniques, and the kinetics model was used to compare the smaller matrix to the expected results of the larger one. The new 21-Test matrix produced a numerical correlation that agreed well with the results from the 41-test matrix, indicating that the smaller matrix will provide the same autoignition information as the larger one with acceptable precision.
Microstructure-Property Relation in a Liquid Crystalline Polymer-Carbon Nanofiber Composite
Authors: Rohatgi A. , Baucom J. N. , Pogue W. R. , Thomas J. P.
Published: April 2008

Microstructure-property relationship is being examined in a polymer matrix composite system consisting of vapor grown carbon nanofibers (VGCF) mixed in a thermotropic liquid crystalline polymer (LCP) matrix. These nanocomposites show an inherent hierarchical structuring, which we hope to utilize in the development of multifunctional structure-conduction composites with improved performance. Among unfilled polymers, extruded LCPs show relatively high strength and high stiffness that have been attributed in the literature to the preferential molecular alignment along the extrusion direction and the hierarchical nature of LCPs. Further, as is typical for polymers, LCPs have poor thermal and electrical conductivity relative to metals. By contrast, carbon nanofibers are known to possess high strength, high stiffness and high conductivity in the axial direction. It is expected that the combination of the extrusion process and the similarity of the length-scales of LCP fibrils and carbon nanofibers will lead to improved axial alignment of both phases within the nanocomposite filaments. This simultaneous alignment of the LCP matrix and that of the carbon nanofibers is expected to lead to interesting mechanical and conductive behavior in the nanocomposite filaments through hierarchical interactions at the nanometer to micrometer scale levels. Carbon nanofibers, 60-150 nm in diameter, were mixed with Vectra A950 LCP and the mixture was extruded as 0.5–2 mm diameter filaments. Nanocomposite filaments with 1%, 2%, 5% and 10 wt.% VGCF were characterized via tensile testing and fractography. The tensile modulus, failure strength and strain-to-failure were found to be sensitive to filament diameter, carbon nanofiber content and extrusion process. There was a noticeable increase in mechanical performance with decreasing filament diameter irrespective of carbon nanofiber content. Fracture surfaces showed hierarchical features from nanometer to micrometer scale and processing defects in the form of voids. The results of this research will be used to fabricate composite components that exploit structural hierarchy from nano-to macro-scale.