bluuebunny/crossref_metadata_2025 huggingface dataset:
Damage Progression Identification in Woven Composites With Fiber Bragg Grating Sensors
Authors: Pearson James , Prabhugoud Mohanraj , Zikry Mohammed , Peters Kara
Published: April 2008

In this study, measurements from low-impact velocity experiments including embedded and surface mounted optical fiber Bragg grating (FBG) sensors were used to obtain detailed information pertaining to damage progression in two-dimensional laminate woven composites. The woven composites were subjected to multiple strikes at 2m/s until perforation occurred, and the impactor position and acceleration were monitored throughout each event. From these measurements, we obtained dissipated energies and contact forces. The FBG sensors were embedded and surface mounted at different critical locations near penetration-induced damaged regions. These FBG sensors were used to obtain initial residual strains and axial and transverse strains that correspond to matrix cracking and delamination. The transmission and reflection spectra were continuously monitored throughout the loading cycles. They were used, in combination with the peak contact forces, to delineate repeatable sensor responses corresponding to material failure. From the FBG spectra, fiber and matrix damage were separated by an analysis based on signal intensity, the presence of cladding modes, and the behavior of individual Bragg peaks as a function of evolving and repeated impact loads. This provided an independent feedback on the integrity of the Bragg gratings. A comparison by number of impact strikes and dissipated energies corresponding to material perforation indicates that embedding these sensors did not affect the integrity of the woven systems and that these measurements can provide accurate failure strains.
Coupled Torsional Vibrations in Drilling Systems
Authors: Khulief Y. A. , Bashmal S. , Al-Sulaiman F. A.
Published: April 2008

The contact between the drilling bit and formation is known to excite severe torsional and axial vibrations in the drillstring. A dynamic model of the drillstring including both drillpipe and drillcollars is formulated. The equation of motion of the rotating drillstring is derived using Lagrangean approach together with the finite element method. The model accounts for the gyroscopic effect, the torsional/bending inertia coupling, the axial/bending geometric nonlinear coupling, and the stiffening effect due to the gravitational force field. Reduced order modal form of the dynamic equations is obtained using complex modal transformation. The developed model is integrated into a computational scheme to calculate time-response of the drillstring due to torsional excitations.
Nano-Scale Abrasion Studies of Materials Used in MEMS Devices and Packages
Authors: Park Jong M. , Mutlu Senol , Gianchandani Yogesh B.
Published: April 2008

Abrasion plays an important role in the manufacture and use of certain microstructures. In this paper, we explore the nano-scale abrasion characteristics of Al, Si, Pyrex™ glass, and glass-mica ceramic (Macor™), using a commercial scribing tool adapted to provide controlled velocity and force, and accurate positioning for abrasion utilizing two abrasion heads: a diamond facet edge and a custom alumina-grit head. While Al is easily abraded, it tends to create build-up of material along the edges. Silicon provides triangular clean groves with minimum widths ≈ 460 nm. Macor provides scalloped grooves that show some chipping and have minimum widths of ≈ 320 nm. Glass provides clean, rounded grooves, with minimum widths of ≈ 200 nm. This paper also describes how controlled abrasion can be exploited for the non-lithographic fabrication of nanochannels which are of interest in several fluidic devices.
A Selective Mixing in Microfluidic Systems Using Bacterial Chemotaxis
Authors: Kim Min Jun , Breuer Kenneth S.
Published: April 2008

We demonstrate the use of Escherichia coli and their chemotactic characteristics to enhance mixing in a microchannel in a controlled and bi-directional manner. The presence of a chemoattractant in one arm of a three-junction microchannel results in an asymmetric increase in the effective diffusion coefficient of Dextran, which rises linearly with the concentration of attractant from a baseline value of 8 μm2/s to 42 μm2/s at a concentration of 0.1 M. The response to repellent is similar, with the opposite bias.
Precision Tracking Controller Design for High Speed Feed Drives
Authors: Erkorkmaz Kaan , Altintas Yusuf
Published: April 2008

This paper investigates the effectiveness of adaptive sliding mode control (SMC) for precision tracking in high speed machine tool drives. Dynamics of the feed drive, comprising of rigid body motion, guideway friction and ball screw vibrations, are identified. Two strategies are developed. The first one considers rigid body dynamics in the plant and compensates for the resonance with a notch filter. The second controller considers the first torsional mode as part of the plant and actively suppresses its vibrations. The two controllers are evaluated in frequency domain analyses and simulations. The results indicate that the notch filter based design is easier to implement and possesses comparable tracking, disturbance rejection, and robustness to the mode-compensating SMC. The simulation results are verified in tracking tests where 1.5 [um] of accuracy is achieved at a feed speed of 250 [mm/sec].
A Comparative, Experimental Study of Model Suitability to Describe Vehicle Rollover Dynamics for Control Design
Authors: Cameron John T. , Brennan Sean
Published: April 2008

This work presents results of an initial investigation into models and control strategies suitable to prevent vehicle rollover due to untripped driving maneuvers. Outside of industry, the study of vehicle rollover inclusive of both experimental validation and practical controller design is limited. The researcher interested in initiating study on rollover dynamics and control is left with the challenging task of identifying suitable vehicle models from the literature, comparing these models with experimental results, and determining suitable parameters for the models. This work addresses these issues via experimental testing of published models. Parameter estimation data based on model fits is presented, with commentary given on the validity of different methods. Experimental results are then presented and compared to the output predicted by the various models in both the time and frequency domain in order to provide a foundation for future work.
New Approaches for Sample-Profile Estimation for Fast Atomic Force Microscopy
Authors: Salapaka Srinivasa M. , De Tathagata , Sebastian Abu
Published: April 2008

The Atomic Force Microscope (AFM) is a powerful tool for imaging and manipulating matter at the nanoscale. The sample-profile estimation problem in Atomic Force Microscopy is addressed using H∞ control. A new estimate signal for the sample profile is proposed and it is proved that this signal tracks perfectly the profile signal. i.e., the transfer function between the profile signal and the estimate signal is one. Experimental results are presented to corroborate these results.
Phase Transitions in the Multi-Vehicle Task Assignment Problem
Authors: Earl Matthew G. , D’Andrea Raffaello
Published: April 2008

We have developed real-time methods to synthesize cooperative strategies for the multi-vehicle task assignment problem in an adversarial environment. By introducing a set of tasks to be completed by the team of vehicles and a trajectory generation primitive for each vehicle, we formulate the multi-vehicle control problem as a task assignment problem. The continuous component of the problem is captured by the trajectory primitive, and the combinatorial component is captured by task assignment. We have developed an efficient branch and bound solver for the task assignment component of the problem. In this paper, we analyze the computational complexity of our solver with variations in parameters of the problem. We found a phase transition in the ratio of the maximum velocity of opposing vehicles, and we found a phase transition in the ratio of the number of vehicles per team. The results show that the task assignment problem is difficult to solve when the capabilities of the two teams are comparable and easy to solve when one team is more capable than the other.
Shock Wave of Gas-Solid Flow Considering the Two-Phase Sound Velocity
Authors: Zhao Liangju , Gao Lijuan , Chen Qinghua , Gao Hong , Zeng Danling
Published: April 2008

This paper constructs the model of shock wave of gas-solid flow considering the two-phase sound velocity. After the calculations, the results of shock wave are compared with the results by using gas sound velocity. When the gas fraction is high, the results by the two models agree well with each other. When the gas fraction is lower, the two-phase sound velocity model gives more accurate sound velocity. So the shock wave results by the two-phase sound velocity model are more reasonable than by the single-phase sound velocity. The model of this paper is more applicable for two-phase shock wave analysis.
Mathematical Solution for the Determination of Optimal Warehouse Location and Optimal Distribution Route
Authors: Naraparaju Jagannadha Rao , Karamcheti Raghunandan A. , Wang Z. Y.
Published: April 2008

In this paper, a procedure to determine the optimal location of a distribution warehouse, from which products are sent out to a group of companies has been studied. The goal was to minimize annual transportation distance between the warehouse and the customers. Fundamentals of mathematics have been used to formulate a virtual map showing the location of the present customers. Mathematical models and equations were developed making certain assumptions and an optimal location for the warehouse has been determined. Various factors that are involved in relocating the warehouse have been considered. Also a solution is given for the optimal location of a satellite or an auxiliary warehouse in addition to the existing one. A case study has been conducted on the model with the help of various numerical examples. Based on the optimal location of the relocated warehouse and the satellite warehouse obtained, the reductions in the transport costs were estimated. Once the optimal warehouse location has been found out, the next step was to find out an optimal route (least travel distance) for a practical case in which several companies have to be supplied with necessary products from one warehouse in a single trip. For this purpose, mathematical models were created and optimal routing algorithms were developed. Case studies have been conducted with the help of numerical examples. High amounts of savings in terms of travel distances, costs and time could be observed by the implementation of these algorithms.
An E-Operation Management System for Focused Manufacturing
Authors: Pounder P. , Williams G.
Published: April 2008

A fresh approach to endorsing electronic operations (e-ops) management processes in an act to focus manufacturers by leveraging information and disseminating it in an appropriate manner. This approach allows the manufacturer to develop its core competencies while creating a foundation to strengthen the competitiveness of the operation by enhancing the interactivity between the supply chain management (SCM), customer responsive management (CRM) and corporate management (CM). The research concentrates on the Small and Medium-sized Manufacturer (SMM), as part of a group known for its limitations in finances, personnel and equipment resources. Therefore the research involves the appropriate progression of processes and the assignment of appropriate resources to carry out the processes. To achieve the goals of a more competitive manufacturer/world class manufacturer (WCM), the research develops a model and a road map for execution that is easily adaptable by SMMs. Finally, this research proposes that its e-ops tool will connect the SCM, CRM, and CM in a manner that does not call for a total revamp of the operations but rather it just strengthens the existing processes given the manufacturer’s constraints.
Stress-Dependent Water Uptake Behavior of Clay Reinforced Nanocomposite Epoxy
Authors: Sancaktar E. , Kuznicki J.
Published: April 2008

Layered silicate nanolayers can be used as alternative inorganic components for the construction of nanostructured hybrid composites. The clay silicate nanolayers possess stable Si-O bonds and high particle aspect ratios comparable to conventional fibers. Their interlayer surface is easily modified by ion-exchange reaction, and the gallery can be intercalated by organic polymer precursors for the formation of organic-inorganic nanocomposites. Exfoliated clay composites contain single, 1 nm thick layers of clay dispersed in the polymer matrix. Owing to the platy morphology of the silicate layers, exfoliated clay nanocomposites can exhibit dramatically improved properties such as barrier and mechanical properties that are not available for conventional composite materials. Since the clay particles scavenge water, the nanocomposite samples initially absorb slightly higher amounts of water in comparison to the no-clay samples, with the water molecules congregating around the clay particles. On the other hand, the presence of these clay particles still hinders diffusion of water through the sample, thus protecting the structural interfaces. In this work, low viscosity liquid aromatic diglycidyl ether of bisphenol A (DGEBA) epoxy resin Epon 815C was mixed with nanoclay at 60°C for 6 hours. The epoxy-clay mixture was then mixed with curing agent DETA (Diethylenetriamine) at 80°C for 4 minutes and cured at 120°C for 3 hours to produce exfoliated clay — epoxy resin system. These samples were used to first optimize the percent clay level for lowest water uptake, and subsequently immersed in water in stressed condition (flexural stress) to assess the effect of stress on nanocomposite epoxy system for its water uptake behavior. The results revealed up to 33% reduction in water uptake for the stressed samples.
A Residual Based Variational Method for Reducing Dispersion Error in Finite Element Methods
Authors: Thompson Lonny L. , Kunthong Prapot
Published: April 2008

A difficulty of the standard Galerkin finite element method has been the ability to accurately resolve oscillating wave solutions at higher frequencies. Many alternative methods have been developed including high-order methods, stabilized Galerkin methods, multi-scale variational methods, and other wave-based discretization methods. In this work, consistent residuals, both in the form of least-squares and gradient least-squares are linearly combined and added to the Galerkin variational Helmholtz equation to form a new generalized Galerkin least-squares method (GGLS). By allowing the stabilization parameters to vary spatially within each element, we are able to select optimal parameters which reduce dispersion error for all wave directions from second-order to fourth-order in nondimensional wavenumber; a substantial improvement over standard Galerkin elements. Furthermore, the stabilization parameters are frequency independent, and thus can be used for both time-harmonic solutions to the Helmholtz equation as well as direct time-integration of the wave equation, and eigenfrequency/eigenmodes analysis. Since the variational framework preserves consistency, high-order accuracy is maintained in the presence of source terms. In the case of homogeneous source terms, we show that our consistent variational framework is equivalent to integrating the underlying stiffness and mass matrices with optimally selected numerical quadrature rules. Optimal GGLS stabilization parameters and equivalent quadrature rules are determined for several element types including: bilinear quadrilateral, linear triangle, and linear tetrahedral elements. Numerical examples on unstructured meshes validate the expected high-order accuracy.
Calculating Friction Force by the Variation of Potential on the Contact Surfaces During Sliding
Authors: Xu Zhongming , Huang Ping
Published: April 2008

In the present paper, a method based on energy dissipation mechanism of the Independent Oscillator Model is used to calculate friction force and friction coefficient of two flat surfaces with a relative motion. The method is simplified to calculate friction work by the potential change of contact surfaces during sliding, which can be gained by a universal adhesive energy function. The results reveal the relationships between friction force and parameters of a tribo-system such as surface energy and microstructure of interfacial material. The numerical solutions of the known experimental data agree with that of Bowden’s equation, and they agree with Lantz’s experimental results carried out with an ultra high vacuum atomic-force microscope as well. It shows the method is practical.
A Probabilistic Analysis for Vibration of Rotating Beams With Uncertain Parameters
Authors: Wang Z. Q. , An L. Q. , Peng Z. Z.
Published: April 2008

In this paper, the material properties, sectional properties, rotating speed and the boundary condition of beam are treated as random variable. A Ritz method is used to derive the eigenvalues equation of the rotating beam with uncertain parameters. A matrix perturbation technique is employed to obtain probabilistic characters of the natural frequencies and vibration modes for free vibration. The sensitivity analysis is performed to study the influence of parametric changes on the variation of nature frequencies. The effects of variation in material propertied, rotating speed and the joint stiffness on the deterministic part of natural frequencies and vibration modes, the covariance and the coefficient of variance (COV) for the nature frequencies are investigated. A numerical example is studied by the present method and the Monte Carlo simulation to establish the validity of the present method.
Annealing Effects on the Flexible OLED Substrates
Authors: Yu Hsin Her , Hwang Shug June
Published: April 2008

A novel flexible polymer for the new generation display panel was prepared with different annealing treatments; AFM and spectroscopy were employed to measure the surface roughness and the optical transparency of the substrates. Electroluminescence spectra of FOLED (flexible Organic light emitting diode) with different annealing times and temperatures were investigated.
Creep-Fatigue Strength of Sn-8Zn-3Bi Solder Under Multiaxial Loading
Authors: Yamamoto Takaei , Itoh Takamoto , Sakane Masao , Sasaki Hiroshi , Shuto Kazuhiko , Tsukada Yutaka
Published: April 2008

This paper describes the multiaxial creep-fatigue of Sn-8Zn-3Bi solder in proportional and non-proportional loadings. Push-pull and reversed torsion tests were carried in proportional test using fast-fast, slow-fast, fast-slow, slow-slow and strain-hold waves. Non-proportional tests were also carried out using box, step and circle strain waves. In proportional test, smallest creep-fatigue lives were observed in push-pull slow-fast test. Creep-fatigue lives in reversed torsion test were longer by a factor of 2 than those in push-pull test compared with the same strain wave. Non-proportional loading reduced the creep-fatigue life. Circle strain wave showed the smallest fatigue life in non-proportional loading. A non-proportional strain proposed by the authors correlated all the proportional and non-proportional fast-fast data within a factor of two scatter band.
Simulation of Turbulent Flows Over Moving Sinusoidal Waves
Authors: Roberts Richard A. , Cui Jie
Published: April 2008

In this study, turbulent flow over moving sinusoidal waves with different wave slope and wave speed is investigated by solving the Reynolds-averaged Navier-Stokes (RANS) equations using a commercial computational fluid dynamics (CFD) software package. The RANS models include the κ-ε, κ-ω, and Reynolds stress formulations. The results show that the imposed waves significantly influence the pressure and friction stress, and velocity distributions. The performance of the turbulence models was presented, and the effects of wave slope and wave speed were compared and discussed.
Design of a Model Based Controller for Regulation of Auto-Ignition
Authors: de Ojeda William
Published: April 2008

The present paper considers a model predictive controller to sustain a combustion system that relies in the auto-ignition of a fuel/air mixture. The auto-ignition process relies in elevating the fuel/air mixture to the ignition temperature to initiate the combustion process. The homogeneity or heterogeneous characteristics of the mixture have a strong influence on the process as well as the fuel composition, Diesel or gasoline, and charge mixture temperature. The auto-ignition process is examined in a compression ignition (CI) engine platform, with Diesel fuel premixed early in the compression cycle with the charge air. The variations in the temperature of the charge air in each cylinder encountered due to variations in cooling in the cylinder head or unsymmetrical flow characteristics are compensated using a model predictive controller to manipulate the intake valve closing timing (IVC). IVC regulates the effective compression ratio and the timing with respect to the cylinder’s top dead center position when the charge temperature reaches the auto-ignition temperature. Simultaneously, the controller manipulates the fuel mass delivered to the cylinder to adjust torque to the desired level. The paper shows empirical correlations between the intake valve closing and fueling to auto-ignition timing and torque that serve to solve the predictive model when subject to various noise factors.
Performance Conversion of Centrifugal Oil Pumps Used for Transporting Viscous Oil in China
Authors: Xue Dun-Song , Cao Guang-Jun
Published: April 2008

Researchers in University of Petroleum of China (UPC) have done extensive lab studies to understand how the centrifugal pumps used in China perform in various conditions when being used for transporting viscous oil. Measurement errors of fluid rate are corrected online, while oil viscosity is also accurately recorded. Using these lab data and based on the most updated hydraulic models for centrifugal pumps in China, a set of performance conversion charts for different pump head, rate, efficiency, and net positive suction head are generated. In addition, the authors converted these curves to mathematical functions using statistical regression. It is found that the results calculated from the regressed functions are as accurate as those looked-up from the performance conversion charts, with total error within 0.4%. This approach has an advantage over the traditional graphical lookup approach in that the functions can be easily be coded in software applications. The authors have also converted the performance curves used in U.S., Russia and German to mathematical functions and noted that similar accuracies are achieved.
Laminar Natural Convection Inside a Wavy Enclosure Heated From Top and Uniformly Cooled From the Bottom and Both Sides
Authors: Dalal Amaresh , Das Manab Kumar
Published: April 2008

In the present paper, natural convection inside a square cavity with one and three undulations on the top wall has been carried out. The top wall is heated by a spatially varying temperature and other three walls are kept constant lower temperature. The integral forms of the governing equations are solved numerically using finite-volume method in non-orthogonal body-fitted coordinate system. SIMPLE algorithm with higher-order up-winding scheme are used. The streamlines and isothermal lines are presented for different Rayleigh number (103-106) and a fluid having Prandtl number 0.71. Results are presented in the form of local and average Nusselt number distribution for two different undulations (1 and 3) with wave amplitude of 0.05.
Stability and Performance Analysis of a Metering Poppet Valve
Authors: Fales Roger
Published: April 2008

Poppet type metering vales have many benefits including low leakage and an economical design. These benefits make the poppet valve an appealing alternative to spool valves in a valve stack. The fact that the metering element is not hydrostatically balanced as in a spool valve leads to control design challenges. In this work, a model of an electro hydraulic metering poppet valve is considered. Due to design compromises, the response of production metering poppet valves tends to be too slow to maintain a desired flow rate when there are fast upstream pressure variations. Re-designing to speed up the response of the valve may lead to stability issues which can be traced to plant uncertainty. Frequency response analysis of the valve model shows that the model varies greatly depending on the operating point chosen for the linearization. The analysis presented will help define the problem of designing hardware and control systems for higher performance but still reliable metering poppet valves.
Measurement of the Velocity Profile Near the Wall in Bio-Fluid Flow Using Evanescent Light Source
Authors: Kanda Kensuke , Ogata Satoshi , Yang Ming
Published: April 2008

For the investigation of near surface phenomena, a novel method, which is to measure velocity profile in the direction of depth, are suggested. By changing the angle of induce light, illuminated penetration depth is changed. The velocities of fluorescent tracers are successfully measured using PTV technique. The fluid including bio-molecules is employed for velocity measurement. The velocity profile of bio-fluid is measured by eliminating the influence of the Brownian motion of tracers. The velocity profile of the flow agrees well with the plane Poiseruille flow equation except for the results at large distance from the wall. It is assumed that the difference in the velocity at the large distance results from the inhomogeneous concentration profile due to surface potential. In our knowledge, the method suggested in this study is the first one in terms of measuring flow velocity profile in direction of depth near wall surface.
Impact of Fuel Cell Degradation on the Efficiency of the Hybrid System High Temperature Fuel Cell/Turbine and Ways to Mitigate the Power Loss
Authors: Karvountzi Georgia C. , Duby Paul F.
Published: April 2008

The performance and life of a fuel cell is strongly affected by the voltage degradation that results from increase of overpotentials and loss of electrolyte conductivity overtime. The lack of valid field data makes degradation difficult to quantify. The few degradation rates reported in the literature so far vary from 0.3% to 0.6% per 1000 hours of operation for the MCFC, and 0.1% to 0.25% per 1000 hours of operation for the SOFC. We performed a parametric analysis to investigate the impact of fuel cell degradation on the overall hybrid system efficiency. We considered fuel cell power loss due to cumulative degradation varying from 1% up to 20% in two different degradation scenarios for each one of MCFC and SOFC. We considered several ways to recover part or all of the lost system efficiency. An optimization of the fuel cell subsystem design as well as the timing of replacement of stacks or cells that operate poorly, leads to complete efficiency recovery. The use of a stand-by gas turbine is an alternative way to produce the power lost by the fuel cell subsystem. However gas turbines are less efficient than the fuel cells and the recovery of the lost power carries a penalty in system efficiency. Cost considerations have also been taken into account. Stack replacement maintains the system high efficiency but leads to higher system capital cost, because the fuel cell stack is the most expensive component of the system. The use of stand-by gas turbines reduces initial costs but operating costs increase because of the lower system efficiency.
Pneumatic Brake Actuator Design and Modeling for the Precision Stopping Control of Automated Bus
Authors: Bu Fanping , Tan Han-Shue
Published: April 2008

Precision stopping is an important automated vehicle control function that is critical in applications such as precision bus docking, automated truck or bus fuelling, as well as automatic intersection or toll booth stopping. The initial applications of this technology are most likely to be applied to heavy-duty vehicles such as buses or trucks. Such applications require specific attention to brake control since the characteristics of a typical pneumatic brake system of a heavy vehicle is inherently nonlinear with large uncertainties. The feasibility of providing a smooth precision stopping brake control based on a conventional pneumatic brake system has not yet been demonstrated. As the first step toward the fine braking control of conventional pneumatic brake system, this paper describes the design of a pneumatic brake actuator based on the “off-the-shelf” components for the precision stopping control of an automated bus and details the modelling of each components. In order to facilitate controller design, the complex “component by component” model is reduced to a more tractable one which still preserves the basic nonlinear characteristics of the original system. Both physical explanation and experimental data are provided to justify the model reduction and validate the simplified model which is used for controller design in [1.]
FEM Stress Analysis and Sealing Performance in Pipe Flange Connections With Adhesive Subjected to Internal Pressure and External Bending Moments
Authors: Katsuo Masahide , Sawa Toshiyuki , Kikuchi Yuki
Published: April 2008

This study deals with the stress analysis and the estimation of sealing performance of the pipe flange connections with an adhesive under an internal pressure and an external bending moment are analyzed by using the 3-dimensional elastic finite element method (FEM). The experiment of the leakage test of the connections with an adhesive was carried out by applying the above loads to the connections. From the FEM analysis, the following results were obtained; (1) when an internal pressure is applied to the flange connections, the compressive stress at the interface between a flange and an adhesive increases proportionally from the inner side of the interface to outside, and (2) when an internal pressure and a bending moment apply to the flange connections, the stress distribution at the half part of the interface increases as the external bending moments increase and also Young’s modulus of the adhesive increases. From the experiments, the following results were obtained: (1) sealing performance of the pipe flange connections with an adhesive under an internal pressure and an external bending moment increases as the flange thickness and an initial clamping force of bolts increases and (2) the sealing performances were not found between the connections with an adhesive and that with a gasket combining an adhesive. Furthermore, the numerical results are in fairly good agreement with the experimental results.
A Finite Element Based Inverse Method for Two-Dimensional Heat Conduction Problems
Authors: Subramanian Kannan , Cherukuri Harish P.
Published: April 2008

An inverse method for predicting surface heat fluxes as functions of time and space was developed and applied to several one-dimensional problems by Ling et al. [1]. The method is based on the Galerkin finite element method and takes advantage of the linearity between the computed temperatures and the instantaneous surface heat fluxes. In the present work, the method is extended to two-dimensions and applications are made to a rectangular domain and an axisymmetric domain. Several possibilities are considered for solution stabilization and the effect of these approximations on the flux predictions is analysed. Results from a study of the sensitivity of the fluxes to the temperature sensor locations are also presented.
Droplet Breakup in Shear and Elongation Dominated Flows in Microfluidic Devices
Authors: Anna Shelley L. , Christopher Gordon F. , Noharuddin Nadia
Published: April 2008

Microfluidic devices have recently been demonstrated as an effective platform for generating monodisperse drops and bubbles, which is important for applications from emulsification to drug delivery and lab on a chip. Here we compare drop formation mechanisms in microfluidic devices in which flows can be either predominantly shear flows, or predominantly elongational flows. In either case, drops of an aqueous liquid form due to viscous stresses imposed by a second oil phase. We show that the two flow types lead to dramatically different ability to control droplet sizes. We characterize the drop size over a large number of experiments by varying capillary number, volume fraction, and viscosity ratio. We observe distinct breakup modes depending on these three dimensionless parameters, and the flow type.
Advancements in Fail Safe Response With Bistable Composite Structures
Authors: Whitman Zachary L. , La Saponara Valeria , Adams Daniel O. , Leelavanichkul Seubpong , Cherkaev Andrej , Cherkaev Elena , Vinogradov Vladimir
Published: April 2008

Cars have dent resistant side panels, crumple zones and composite bumpers to absorb and disperse impact energy protecting occupants. Each of these improvements share a common feature: once activated or deformed, their load carrying capacity is diminished. A bistable structure is such that, once activated, it has a second stronger phase which has the ability to sustain higher loads. This allows for a better distribution of damage, and in addition the structure keeps its integrity for a longer time. Initial tests have verified this concept proving that a bistable structure under tensile loading has the capacity of absorbing more energy than a similar monolithic structure under the same load conditions. Bistable structure behavior has also been shown for a system composed of advanced fiber reinforced composites, which has the potential of being a break-through for applications where energy absorption is sought.
Self and Directed Colloidal Assembly on Patterned Electrodes
Authors: Bahukudumbi P. , Bevan Michael A. , Beskok Ali
Published: April 2008

Clustering of colloidal particles near an electrode surface during and after electrophoretic deposition has been reported in the literature [1, 2, 3, 4]. The aggregation of colloidal particles has made the precise assembly of two and three dimensional colloidal crystals possible. In this paper, we demonstrate the use of external electric fields to sensitively tune the interactions between colloidal particles to form ordered structures. The directed assembly of colloidal particles on patterned electrode surfaces is also investigated as a means of building three-dimensional nanostructures. Finally, a new method to map potential energy landscapes of templated substrates using a diffusing colloidal particle as a sensitive local energy probe is described.
A Neuro-Fuzzy Model for Simulating Outer Hair Cell of Human Cochlea
Authors: Thumati Balaje T. , Naidu D. Subbaram , Stout Larry
Published: April 2008

Understanding the functioning of the human auditory system has been of interest for decades and many mathematical models have been developed based on experimental results. Many of these models address the key components of the human auditory system: outer ear, middle ear, and inner ear, which consists of cochlea and organ of corti. In this paper, a novel approach for human auditory model is developed that is based on the concepts of fuzzy logic for simulating basilar membrane and stereocilia, and a feed-forward neural network for simulating outer hair cell of the inner ear. Frequency, intensity and the direction of stereocilia movement are the three inputs to the fuzzy logic portion of the model. The output of this block is the net force, which becomes the input to the neural network. The implementation and simulated results using MATLAB® are presented.
A New Model for MacPherson Suspension System and Observation of Ride Characteristics and Its Optimal Control
Authors: Fallah M. S. , Fardisi S. , Eghtesad M.
Published: April 2008

In this paper a new model for the MacPherson suspension system and its optimal control are investigated. The focuses of the modeling were to add the rotational motion of the unsprung mass and considering physical characteristics of the spindle such as mass and inertia moment. The vertical acceleration of the sprung mass is measured, while the angular displacement of the control arm is estimated. According to this model the ride characteristics such as alterations of the camber angle, king-pin angle and track are displayed. This model is more general in the sense that it provides an extra degree of freedom in determining the plant model for control system design. Optimal control theory was employed to derive a control law for an active suspension system. The performance degradation with an active actuator is evaluated. Simulations are also provided.
Hybrid Control for UAV-Assisted Search and Rescue
Authors: Ryan Allison D. , Nguyen David L. , Hedrick J. Karl
Published: April 2008

We develop a decentralized hybrid controller for fixed-wing UAVs assisting a manned helicopter in a United States Coast Guard search and rescue mission. The UAVs assist the manned helicopter by providing an expanded sensor footprint using onboard cameras. We consider two UAVs, one flying on either side of the helicopter, with constant velocity and maximum turn rate constraints. Tracking the helicopter around sharp corners will be difficult due to these constraints and the difference in path lengths for the two UAVs. To solve this problem, we propose a hybrid controller that allows the UAVs to swap positions in an attempt to improve the tracking and ground coverage performance of the formation. We discuss tracking control, the position swapping algorithm and collision avoidance. Simulation results demonstrate improved search efficiency and aircraft safety.
Reliability Evaluation of BGA Solder Joints by Using Thermal Fatigue Models
Authors: Lee Ouk Sub , Myoung No Hoon , Kim Dong Hyeok
Published: April 2008

The use of Ball Grid Array (BGA) interconnects utilizing the BGA solder joint has grown rapidly because of its small volume and diversity of its application. Therefore, the continuous quantification and refinement of BGA solder joint in terms of its reliability are required. The creep and cyclically applied mechanical loads generally cause metal fatigue on the BGA solder joint which inevitably leads to an electrical discontinuity. In the field application, the BGA solder joints are known to experience mechanical loads during temperature changes caused by power up/down events as the result of the Coefficient of Thermal Expansion (CTE) mismatch between the substrate and the Si die. In this paper, extremely small resistance changes in the lead free joints corresponding to the through-cracks generated by the thermal fatigue were measured and the failure was defined in terms of anomalous changes in the joint resistance. Furthermore, the reliability of BGA solder joints under thermal cycling was evaluated by using a criterion that may define and distinguish a failure in the solder joint. Any changes in circuit resistance according to the accumulated damage induced by the thermal cycling in the joint were recorded and evaluated by the First Order Reliability Method (FORM) procedure in order to quantify the reliability of solder joint. The first order Taylor series expansion of the limit state function incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. Various thermal fatigue models are utilized in this study. Models based on various plastic-strain rates such as Coffin-Manson fatigue model, total strain fatigue model and Solomon fatigue model are utilized in this study. The effects of random variables such as the CTE, the pitch of solder joint, the diameter of solder joint, and the CTE difference solder joints on the failure probability of the solder joint are systematically investigated by using a failure probability model with the FORM.
Multilayer Insulation Venting During Payload Depressurization
Authors: Cotoros Ingrid , Hashemi Ab
Published: April 2008

Multilayer Insulation (MLI) blankets consist of closely spaced aluminum coated shields that are spaced apart to reduce heat transfer between the payload and the environment, particularly in vacuum. In space application, satellite systems and sub-systems are wrapped in MLI blankets to thermally isolate them from the environment and achieve thermal control requirements. During spacecraft launch, the payload undergoes a rapid depressurization before reaching steady state condition. The MLI blankets are usually perforated and/or connected at the boundaries with Velcro strips to allow out-gassing. The blankets can lose their integrity and functionality if the depressurization process is too rapid: the out-gassing flow can tear the perforations, and the pressure differential built-up across the blanket can pull the Velcro strips apart. This paper describes the design and modeling of depressurization through X-slits cut into the blanket and Velcro strips taped along the sides. A methodology is developed, and a model for quantifying the pressure differential build-up is described and applied to a payload enclosure aboard a Delta II rocket.
Finite Element Stress Analysis and Evaluation of the Sealing Performance in Pipe Fittings With Adhesive for Threaded Connections Under Internal Pressure and Bending Moment
Authors: Ishimura Mitsutoshi , Katsuo Masahide , Sawa Toshiyuki , Serizawa Masamichi
Published: April 2008

In practice, PTFE tape is being used for sealing of a pipe fitting. However, the efficiency, the decrease in work time, and the sealing performance can be improved by using adhesive instead of the tape. When such a pipe fitting is under an internal pressure and external bending moment by an internal fluid and others, however, an influence in the sealing performance is taken by how to use an adhesion. This study deals with the stress analysis and the evaluation of the sealing performance of the pipe fitting with an adhesive under an internal pressure and an external bending moment analyzed by using the 3-dimensional elastic finite element method. Furthermore, the experiment of the leakage test of the pipe fitting with an adhesive was carried out when the above loads were applied to the pipe fitting. From 3-D FEM analysis, the following results were obtained: (1) the stress distribution at the interface between thread and adhesive on the side of the internal pressure is tensile stress, and stress on the opposite side is compressive, (2) the stresses at the area of the clearance between the valley of the screw and the mountain increase as the numbers of turns of the thread in fittings increase, and (3) the compressive stress at the side of the tensile part in the fittings decrease as the external bending moments increase. However, the sealing performance will not change when the bending moment is not so great because the compressive stress at the side of the compressive part in the fitting increases. From the leakage tests, the following results of the sealing performance were obtained: (1) the sealing performance of a fittings with adhesive under an internal pressure and a bending moment didn’t decrease when bending moment was not so great, and (2) when it exceeds fixed pressure, rapid leakage from the fitting with adhesive occurred by the exfoliation of the adhesive. Furthermore, the numerical results are in fairly good agreement with the experimental results.
Study on Aerostatic Guidance: Discussion of Flux Coefficients of Orifice
Authors: Zhao Peng , Satomi Tadaatsu
Published: April 2008

In recent years the aerostatic guidance has been used as a precision positioning apparatus in the Integrated Circuit manufacturing or bioengineering field. The purpose of this study is to examine the relationship between the squeeze part of aerostatic guidance and the mass flux, and to make the theoretical calculation on the aerostatic guidance more accurate, when designing an aerostatic guidance. In this study we produced a measurement device to obtain the flux characteristics of the compressed air passing through an orifice with 0.4mm diameter. We used this measurement device to obtain the flux coefficient of the orifice where the air is blowing out in a direction vertical to the guidance surface. The pressure distribution of the guidance surface was measured and the static load characteristic experiment was carried out. Then the experiment values obtained thereby were compared with theoretical values. The results show that although the flux coefficient could be dealt with a fixed value in the region of orifice-squeeze1) when the flux coefficient was calculated from the flux characteristics, it was no longer a fixed value in the region of self-squeeze1). This is considered a cause of the remarkable error in the above-mentioned design calculation result. Thus, in this study the influence of the inner surface roughness (of the orifice) affecting the flux characteristics was clarified and a novel flux formula, where the flow in the boundary layer is taken into account, is devised and formed. As a result, we have established an improved design scheme and theory by which the theoretical computation on the aerostatic guidance can be performed with more sufficient accuracy.
Design and Testing of Passive Sensor Cooling Using Phase Change Material
Authors: Pecson Julie , Perkins Craig , Hashemi Ab
Published: April 2008

Passive heat rejection from a weapon system deployed in space is a challenging problem. This paper describes the development of a phase-change material mini heat sink to absorb the heat from a laser diode for the required operational scenario. Three mini heat sinks made of aluminum, copper, and copper tungsten were designed and manufactured. Phase change material (PCM) was selected to accommodate required heat dissipation from a laser diode. Metal fins, attached to the metal casing of the heat sink, were placed into the PCM to uniformly spread the heat and achieve effective heat transfer. Analytical models were developed to predict the performance of the heat sink. The heat sink was manufactured and initially tested in the laboratory with simulated heat load. Then, tests were carried out under prototypical conditions and the performance of the sink was demonstrated. A comparison of the analytical predictions with data also showed excellent agreement. This paper presents the design, modeling, manufacturing, testing, and comparison of the predictions with experimental results.
Thickness Control of Liquid Crystal Film in a Step Bearing by Electric Field Under Dynamic Loading Condition
Authors: Matsumura Yoshiki , Shiraishi Toshihiko , Morishita Shin
Published: April 2008

This paper describes the viscosity variation of a liquid crystal under electric field, and its application to a controllable step bearing. Liquid crystal is known as a homogeneous organic liquid characterized by the long-range order of its molecular orientation. When an electric field is applied to a liquid crystal film as lubricant, the orientational order of molecules becomes parallel to the applied field, which causes apparent viscosity variation. In this paper, a controllable step bearing system was constructed and its dynamic characteristics were studied. When a step load, sinusoidal or earthquake excitation was applied to the bearing pad, the film thickness was successfully controlled to the appointed value by a conventional PID controller. The response frequency was also studied in the experiment.