bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Thermal Transport in Open-Cell Metal Foams: Effect of Periodic Unit Cell Structure
Authors: Krishnan Shankar , Garimella Suresh V. , Murthy Jayathi Y.
Published: April 2008

Direct simulation of thermal transport in open-cell metal foams is conducted using different periodic unit cell geometries. The periodic unit cell structures are constructed by assuming the pore space to be spherical and subtracting the pore space from a unit cube of the metal. Different types of packing arrangement for spheres are considered - Body Centered Cubic, Face Centered Cubic, and the A15 lattice (similar to a Weaire-Phelan unit cell) - which give rise to different foam structures. Effective thermal conductivity, pressure drop and Nusselt number are computed by imposing periodic boundary conditions for aluminum foams saturated with air or water. The computed values compare well with existing experimental measurements and semi-empirical models for porosities greater than 80%. The effect of different foam packing arrangements on the computed thermal and fluid flow characteristics is discussed. The capabilities and limitations of the present approach are identified.
Static and Dynamic Techniques for Residual Stress Measurements in Microelectromechanical Systems
Authors: Vechery Mary , Dick Andrew , Currano Luke , Dubey Madan , Balachandran B.
Published: April 2008

A major concern in the development of microelectromechanical systems (MEMS) is the presence of residual stress. Residual stress, which is produced during the fabrication of multi-layer thin-film structures, can significantly affect the performance of microscale devices. Though experimental measurement techniques are accurate, actual stress measurements can vary dramatically from run to run and wafer to wafer. For this reason, modeling of this stress is a challenging task. Past work has focused on experimental, static techniques for determining residual stress levels in single-layer and bi-layer structures. In this effort, two different experimental techniques are used for determining residual stress levels in four-layer piezoelectrically driven cantilever and clamped-clamped structures. One of the techniques is based on wafer bow measurements, and the other technique is a dynamic technique that is based on parameter identification from nonlinear frequency-response data. The devices studied, which consist of a piezoelectric layer or lead zirconate titanate (PZT) layer, are fabricated with varying lengths, widths, and material layer thickness. The results obtained from the static and dynamic techniques are compared and discussed.
Piezoelectric Microvalve for Flow Control in Polymer Electrolyte Fuel Cells
Authors: Bucci Brian A. , Vipperman Jeffrey S. , Clark William , Hensel J. Peter , Thornton Jimmy , Kim Sungwhan
Published: April 2008

Maldistribution of fuel across the cells of a fuel cell stack is an issue that can contribute to poor cell performance and possible cell failure. It has been proposed that an array of microvalves could promote even distribution of fuel across a fuel cell stack. A piezoelectric microvalve has been developed for this purpose. This valve can be tuned to a nominal flow rate (and failure position) from which the actuator would either increase or decrease the flow rate and fuel. The valve can successfully regulate the flow of fuel from 0.7 to 1.1 slpm of hydrogen in the range of temperatures from 80° to 100°C and has been tested over pressure drops from 0.5 to 1 psi. A bank of these valves is currently being tested in a four-cell stack at the U.S. Department of Energy National Energy Technology Laboratory.
Energy Efficient Mobile Wireless Sensor Networks
Authors: Priya Shashank , Popa Dan , Lewis Frank
Published: April 2008

Wireless sensor networks (WSN) have tremendous potential in many environmental and structural health monitoring applications including, gas, temperature, pressure and humidity monitoring, motion detection, and hazardous materials detection. Recent advances in CMOS-technology, IC manufacturing, and networking utilizing Bluetooth communications have brought down the total power requirements of wireless sensor nodes to as low as a few hundred microwatts. Such nodes can be used in future dense ad-hoc networks by transmitting data 1 to 10 meters away. For communication outside 10 meter ranges, data must be transmitted in a multi-hop fashion. There are significant implications to replacing large transmission distance WSN with multiple low-power, low-cost WSN. In addition, some of the relay nodes could be mounted on mobile robotic vehicles instead of being stationary, thus increasing the fault tolerance, coverage and bandwidth capacity of the network. The foremost challenge in the implementation of a dense sensor network is managing power consumption for a large number of nodes. The traditional use of batteries to power sensor nodes is simply not scalable to dense networks, and is currently the most significant barrier for many applications. Self-powering of sensor nodes can be achieved by developing a smart architecture which utilizes all the environmental resources available for generating electrical power. These resources can be structural vibrations, wind, magnetic fields, light, sound, temperature gradients and water currents. The generated electric energy is stored in the matching media selected by the microprocessor depending upon the power magnitude and output impedance. The stored electrical energy is supplied on demand to the sensors and communications devices. This paper shows the progress in our laboratory on powering stationary and mobile untethered sensors using a fusion of energy harvesting approaches. It illustrates the prototype hardware and software required for their implementation including MEMS pressure and strain sensors mounted on mobile robots or stationary, power harvesting modules, interface circuits, algorithms for interrogating the sensor, wireless data transfer and recording.
Simultaneous Measurement of Temperature and Velocity Using µPIV
Authors: Chamarthy Pramod , Wereley Steven T. , Garimella Suresh V.
Published: April 2008

In μPIV, for a uniform velocity field the displacement of the cross-correlation function gives the velocity of the fluid and the broadening of the peak-width represents the amount of Brownian motion present. In the presence of a linear or a parabolic shear, the shape of the cross-correlation function would have both the Brownian motion information as well as the velocity distribution information. In the present work, the broadening of the cross-correlation function caused by the velocity gradient was subtracted from the total peak broadening in order to isolate the Brownian motion information and thus infer temperature. To the authors' knowledge, this technique has not been applied to measure the temperature of a moving fluid. The experiments were conducted in a gravity driven flow through a tube surrounded by a constant temperature water bath.
Dynamic Geometrical Modeling of Deposited Material in Multilayer Laser Solid Freeform Fabrication Process
Authors: Alimardani Masoud , Toyserkani Ehsan , Huissoon Jan Paul
Published: April 2008

In this paper, a novel algorithm is proposed to develop a 3D transient finite element model of multilayer laser solid freeform fabrication (LSFF) process. The proposed model predicts the clad geometry as a function of time and process parameters including laser power, traverse speed, powder jet geometry, and material properties. In the modeling strategy, the interaction between the laser beam and powder stream is assumed to be decoupled, therefore, the melt pool boundary on the moving substrate is obtained in the absence of the powder stream. Once the melt pool boundary is calculated, a deposited layer is formed based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream. After the deposition of each layer, the effect of this geometrical change into the thermal distribution within the model is considered for thermal analysis of the next layer deposition. In the numerical simulation, the effects of a non-planar surface on the process parameters such as powder efficiency and absorption factor are taken into account. Geometrical aspects of a thin wall of steel AISI 4340 with four layers are numerically simulated by the developed modeling strategy. Numerical results show that with the growth of the number of layers in the wall, the powder efficiency increases while the absorption factor decreases. Experimental and numerical results are compared to verify the accuracy and reliability of the proposed model.
Fracture Behavior of Hydroxyapatite-Filled Polycaprolactone
Authors: Wong Shing-Chung , Baji Avinash
Published: April 2008

This paper reports some fracture characterization results of hydroxyapatite (HAP)-filled poly(ε-caprolactone) (PCL). For the fracture toughness tests, the HAP concentration was steadily increased. The effect of HAP phase in PCL on the fracture and tearing toughnesses was investigated. The techniques of essential work of fracture (EWF) and tear strength were attempted. T-peel test was also used to evaluate the adhesive bond strength between HAP and PCL components using compression molded PCL-HAP-PCL laminates. Little is reported on the interfacial adhesion properties between bioactive components in scaffold development. The influence of PCL layer thickness (1.25, 2.5 and 3.5 mm) on adhesive strength between HAP and PCL was investigated. The adhesion between HAP and PCL components was found to be relatively strong; however, the thickness of PCL layers did not significantly influence the adhesive strength.
Flow Regimes of Newtonian Fluids in Vertical Co-Axial Flows
Authors: Vempati Bhadraiah , Panchagnula Mahesh V. , O¨ztekin Alparslan , Neti Sudhakar
Published: April 2008

This paper presents experimental and numerical results of the interfacial dynamics of liquid-liquid flows when a dispersed phase liquid introduced in a continuous phase liquid flow with an arbitrary inlet velocity profile. The flow dynamics are studied as a function of the individual phase Reynolds and Capillary numbers, viscosity ratio, flow rate ratio, and Bond number. Fully-developed (or self-similar solution) model predicted multiple (one to three) solutions of jet diameter for a range of dimensionless numbers. The critical bifurcation parameters are identified in order to study the jet instability. The fully developed jet diameter solutions are plotted in terms of flow ratio of liquid phases and indicate three solution branches. Experiments have been carried out using Poly Ethylene Glycol (PEG)-Canola oil to investigate the three possible solutions predicted by fully developed theory. The measured values of inner fluid radius agree very well with the lower branch of the three branched solution and the deviation of the experimental results for the rest of the branches is observed to be more than 50 percent. Numerical simulations also have been performed to compare the self-similar solution results of liquid jet radius using FLUENT® software. The results predicted by numerical simulations agree very well with both the lower and upper branches of solution predicted by fully developed theory.
Combining Energy Boundary Element and Energy Finite Element Simulations for Airborne Noise Analysis
Authors: Vlahopoulos Nickolas , Li Sheng , Sun Jiulong
Published: April 2008

The Energy Boundary Element Analysis (EBEA) has been utilized in the past for computing the exterior acoustic field at high frequencies (above ~400Hz) around vehicle structures and numerical results have been compared successfully to test data. The Energy Finite Element Analysis (EFEA) has been developed for computing the structural vibration of complex structures at high frequencies and validations have been presented in previous publications. The frequency range of applicability of the EFEA depends on the dynamic characteristics of the structure. In this paper the EBEA is utilized for computing the acoustic field around a vehicle structure due to external acoustic noise sources. The computed exterior acoustic field comprises the excitation for the EFEA analysis. Appropriate loading functions have been developed for representing the exterior acoustic loading in the EFEA simulations, and a formulation has been developed for considering the acoustic treatment applied on the interior side of structural panels. In order to demonstrate how the new developments can be combined in airborne noise applications, a case study is presented.
The Effect of Honeycomb Relative Density on Its Effective Elastic Properties: A Theoretical and Experimental Study
Authors: Balawi S. , Abot J. L.
Published: April 2008

Honeycombs are discrete materials at the macro scale level but their mechanical properties need to be calculated as a continuum material in order to simplify their design in engineering applications. The effective mechanical properties of honeycombs subjected to quasi-static loading were studied by analytical and numerical means and correlated with experimental results for aluminum honeycombs. In particular, the effective in-plane elastic moduli of honeycombs were studied as a function of their relative density and the full range for the relative density was divided into three regions. Beam models that account for bending, shear and axial deformations and finite element analyses (FEA) of the discrete structure composed of beam and two-dimensional solid elements were correlated with experiments of honeycombs with various relative densities for all regions. It was shown experimentally that the beam models describe well the material response in the direction of the double wall. However, it concludes that the behavior of honeycombs with high relative density can not be described by wall stretching as anticipated in previous reported studies.
Dynamic Analysis for Structure With Composite Substructures and With Compatible and Incompatible Connections
Authors: Butler Shaoluo L. , Dhingra Anoop K.
Published: April 2008

A complex structural assembly often includes components made of isotropic and anisotropic materials and includes components with complex connections such as bolted, riveted, welded, and sliding joints. This paper categorizes the connections into two types, compatible and incompatible interfaces, and their mathematical descriptions are presented. A substructure with composite plate/shell element is provided. An approach, incorporating substructure-component mode synthesis, considering compatible and incompatible interfaces and being capable of handling laminated composite plate/shell (SCMSCIC) is proposed. Coupling equations including laminated composite substructure and including different types of connections between substructures are developed. Examples have shown good agreement from SCMSCIC and entire structure analysis.
Integrated Direct/Indirect Adaptive Robust Control (DIARC) of Hydraulic Robotics Arm With Accurate Parameter Estimates
Authors: Mohanty Amit , Yao Bin
Published: April 2008

In a general Adaptive Robust Control (ARC) framework, the emphasis is always on the guaranteed transient performance and accurate trajectory tracking in the presence of uncertain nonlinearity and parametric uncertainties. However, when secondary purposes such as system health monitoring and prognosis are of equal importance, intelligent integration of output tracking performance oriented direct adaptive robust control (DARC) and the recently proposed accurate parameter estimation-based indirect adaptive robust control (IARC) is required. In this paper, we will consider such a seamless integration for a hydraulic robotic arm. The newly developed IARC design is first applied to the trajectory tracking for the robotic arm but with an improved estimation model, in which accurate parameter estimates are obtained through a parameter estimation algorithm that is based on physical dynamics rather than the tracking error dynamics. An integrated direct/indirect adaptive robust controller (DIARC) is then presented that preserves the excellent transient tracking performance of the direct ARC designs as well as the better parameter estimation process of the IARC design. The proposed Integrated Direct/Indirect Adaptive Robust Controller (DIARC) achieves the controller-identifier separation, thus enabling certain modularity in the controller design.
Numerical Calculation of the Formation and Persistence, or Collapse, of Vortex Pairs in Counter-Current Parallel Channel Flows
Authors: Pillapakkam Shriram , Humphrey Joseph A. C. , Rosales J. L.
Published: April 2008

A numerical investigation has been performed for the time-dependent motion of a constant property, Newtonian fluid in a counter-current shearing flows configuration. In the geometry of interest, two initially separated streams are made to flow counter to each other through a pair of stacked parallel channels of approximately square cross-section. The streams are then made to shear at a common free interface between the two channels. This problem consists of a very simple Cartesian geometry with well posed initial and boundary conditions. However, for the conditions explored the resulting physics are highly non-linear and complex. Starting from rest, the opposing streams in the free interface region initially display the characteristics of a two-dimensional saddle point flow when observed along the spanwise z-direction. Soon thereafter, depending on the shapes of the velocity profiles imposed at the channel inlet planes, two pairs of transversely aligned vortices appear that can be stable or unstable. If the inlet plane velocity profiles are symmetric each of the two channel vortex pairs counter-rotates and they are stable over long periods of time. If, however, the inlet velocity profiles are asymmetric, two opposed antisymmetric co-rotating vortices dominate the flow. The pair of vortices orbit around each other while being stretched by the background saddle-like flow. They ultimately merge and collapse in a burst of chaotic three-dimensional unsteady motion. In this case, the cycle repeats with an average frequency which appears to depend on the Reynolds number. Aside from their fundamental nature, the phenomena observed have potential applications for the controlled mixing of fluid streams at relatively low Reynolds number.
Control of a PEM Fuel Cell Cooling System
Authors: Meyer Richard T. , Yao Bin
Published: April 2008

Previous research has assumed that a perfect Proton Exchange Membrane Fuel Cell (PEMFC) body temperature manager is available. Maintaining this temperature at a desired value can ensure a high reaction efficiency over all operation. However, fuel cell internal body temperature control has not been specifically presented so far. This work presents such control, using a Multiple Input Single Output (MISO) fuel cell cooling system to regulate the internal body temperature of a PEMFC intended for transportation. The cooling system plant is taken from a recently developed hydrogen/air PEMFC total system model. It is linearized and used to design a series of controllers via μ-synthesis. μ-synthesis is chosen since system nonlinearities can be handled as parameter uncertainties. A controller must coordinate the desired fuel cell internal temperature and commanded mass flow rates of the coolant and cooling air. Each linear controller is created for a segment of the expected current density range. Plant parameters are expected to vary over their linearized values in each segment. Also, a common set of μ-synthesis weighting functions has been developed to ease controller design at different operating points. Thus, the nonlinear cooling subsystem can be controlled with a series of current density scheduled linear controllers. Current density step change simulations are presented to compare the controller closed loop performance and open loop response which uses cooling system flow rates taken from an optimal steady state solution of the whole fuel cell system. Furthermore, a closed loop sinusoid response is also given. These show that the closed loop driven internal fuel cell temperature will vary little during operation. However, this will only be true over the range that the cooling system is required to be active.
Extraction Method for Design Principle of Static Behavior of Vehicle Suspension System
Authors: Yu Qiang , Matsui Hideaki , Miyajima Kenzo
Published: April 2008

In recent years, the demand for making a car comfortable is increasing and as a factor which governs the comfort of a car, improvement in the driving-stability is attempted. Although body rigidity, tire characteristic, aerodynamics, etc. are raised as factors affecting the design results, it is known experientially that the influence of a suspension is especially great. Therefore, the design of a suspension system becomes important for making a comfortable car. Generally, the design processes of a complicated system can be finished through three major stages, the concept design, the basic design, and the detailed design. For example, at the stage of detailed design, the design engineers have the CAD data for the manufacture, and at the same time they can develop very accurate computer simulation model from the CAD data to help them to make decision for special design factors. The basic concept of every CAE tool is to generate the analytical model by a series of discrete elements set instead of the physical parts. As a result, it becomes very difficult for the engineers to find the physical mechanism of the complicated behavior of their design from the results of numerical analysis. For the concept design processes, it is very important for the design engineers to understand the basic principle of their basic design plans and to compare with the different concepts to know which one has the highest potential to achieve the design aims. However the engineers have to accomplish these processes by only their experience. In this study, the authors proposed a new method to identify the important information which links to the basic principle of the physical behavior by using CAE technology. This method can help the engineers to grasp the basic physical characteristic that governs the first-order behavior.
Numerical Calculation of the Flow in the Fish Lateral Line Canal: Applications to Predators Tracking Prey
Authors: Barbier Charlotte , Humphrey Joseph A. C.
Published: April 2008

Fish use sensors inside the lateral line trunk canal (LLTC) to detect the motion of water in their surroundings. The LLTC is a complex sensory organ consisting of a long tube no more than a few millimeters in diameter embedded immediately under the skin of the fish on each side of its body. In most fish, pore-like openings are regularly distributed along the LLTC, and a minute sensor enveloped in a gelatinous cupula, referred to as a neuromast, is located between each pair of pores. Drag forces resulting from fluid motions induced inside the LLTC by pressure fluctuations in the external flow stimulate the neuromasts. The present study investigates the motion-sensing characteristics of the LLTC and how it may be used by fish to track prey. A two-level numerical model is presented that couples the surrounding flow outside the LLTC to that stimulating the neuromasts within it. First the unsteady flow past a pair of simulated prey/predator fish in coasting motion is calculated using a Navier-Stokes solver. Then the pressure field associated with this external flow is used to drive the flow inside the LLTC of the predator, which creates the drag forces acting on the neuromast. The model is used to investigate the filtering properties and performance characteristics of the LLTC for a range of unsteady flows of biological interest. The results obtained suggest that the LLTC preferentially filters high frequency pressure gradient oscillations, and hence high frequency accelerations, associated with the external flow.
Promotion of Technology Commercialization and Local Economy Development by Non-Research-Intensive Universities
Authors: Fakheri Ahmad , Fazel Farzaneh
Published: April 2008

In the last 25 years, the research conducted in universities, hospitals, and research institutions has resulted in the creation of over 4500 new companies based on the licenses obtained from these institutions. In the same period, there has been a 1500 percent increase in the number of patents granted to universities. These achievements have been primarily at research universities and research institutions, and have not been enjoyed by the overwhelming majority of educational institutions that are not research-intensive. This paper examines technology commercialization activities at non-research-intensive universities and recommends means by which they can generate more intellectual property in a cost-effective manner. These universities can increase financial opportunities for themselves and their communities and can be more effective in job creation and local economic development by adopting policies that are different from those of their research-intensive counterparts. They can use their resources more creatively to promote creation of intellectual property, faculty entrepreneurship, and interdisciplinary cooperation among faculty
Longitudinal Microdynamics of Piezo-Driven Pipettes in Intracytoplasmic Sperm Injection
Authors: Fan Mingxuan , Agca Yuksel , Critser John , Feng Z. C.
Published: April 2008

The Piezo-driven actuator is widely used as one critical part in the micromanipulation system for routine reproductive experiments such as Intracytoplasmic Sperm Injection (ICSI). The actuator can induce the fast mechanical motion on the pipette tip, which greatly facilitates the microinjection processes. It is of rather importance to choose the appropriate system parameters applied to the actuator. In our paper, we propose a mechanical model of the Piezo-driven actuator. We analyze the longitudinal micro-dynamic characteristics of Piezo-driven pipettes. The transient response of the pipette tip is obtained by numerical methods. We also study the effects of the excitation signals on the dynamics of the tip. The related experimental validation is conducted for our simulation results.
Steady State Response of a Piezoelectric Power Harvesting System
Authors: Shu Y. C. , Lien I. C.
Published: April 2008

We study the steady state response of a piezoelectric generator connected to an AC-DC bridge rectifying circuit plus a resistor as the basis for design analysis. In contrast with estimates obtained by various degrees of approximations in recent literature, a closed form solution is derived under the steady-state operation. We show that the average harvested power density depends on the input vibration characteristics (frequency and acceleration), the electric load, the natural frequency, the density, the mechanical damping ratio, and the overall electromechanical coupling coefficient of the system. With it an effective power normalization scheme is provided in order to compare power harvesting devices of different sizes and with different vibration inputs to estimate efficiencies. The theoretical predictions are validated and found in good agreement with our recent experiment.
Investigation of the Effects of Various Energy and Exergy-Based Figures of Merit on the Optimal Design of a High Performance Aircraft System
Authors: Periannan Vijayamand , von Spakovsky Michael R. , Moorhouse David
Published: April 2008

This paper shows the advantages of applying exergy-based analysis and optimization methods to the synthesis/design and operation of aircraft systems. In particular, an Advanced Aircraft Fighter (AAF) with three subsystems: a Propulsion Subsystem (PS), an Environmental Control Subsystem (ECS), and an Airframe Subsystem - Aerodynamics (AFS-A) is used to illustrate these advantages. Thermodynamic (both energy and exergy based), aerodynamic, geometric, and physical models of the components comprising the subsystems are developed and their interactions defined. Off-design performance is considered as well and is used in the analysis and optimization of system synthesis/design and operation as the aircraft is flown over an entire mission. An exergy-based parametric study of the PS and its components is first presented in order to show the type of detailed information on internal system losses which an exergy analysis can provide and an energy analysis by its very nature is unable to provide. This is followed by a series of constrained, system synthesis/design optimizations based on five different objective functions, which define energy-based and exergy-based measures of performance. The former involve minimizing the gross takeoff weight or maximizing the thrust efficiency while the latter involve minimizing the rates of exergy destruction plus the rate of exergy fuel loss (with and without AFS-A losses) or maximizing the thermodynamic effectiveness. A first set of optimizations involving four of the objecttives (two energy-based and two exergy-based) are performed with only PS and ECS degrees of freedom. Losses for the AFS-A are not incorporated into the two exergy-based objectives. The results show that as expected all four objectives globally produce the same optimum vehicle. A second set of optimizations is then performed with AFS-A degrees of freedom and again with two energy- and exergy-based objectives. However, this time one of the exergy-based objectives incorporates AFS-A losses directly into the objective. The results are that with this latter objective, a significantly better optimum vehicle is produced. Thus, an exergy-based approach is not only able to pinpoint where the greatest inefficiencies in the system occur but appears at least in this case to produce a superior optimum vehicle as well by accounting for irreversibility losses in subsystems (e.g., the AFS-A) only indirectly tied to fuel usage.
A Microscopic Continuum Model of a Proton Exchange Membrane Fuel Cell Electrode Catalyst Layer
Authors: Armstrong K. W. , von Spakovsky M. R.
Published: April 2008

A series of steady-state microscopic continuum models of the cathode catalyst layer (active layer) of a proton exchange membrane fuel cell are developed and presented. These models incorporate O2 species and ion transport while taking a discrete look at the platinum particles within the active layer. The 2-D axisymmetric nonporous Agglomerate Model of Bultel, Ozil, and Durand (2000) implemented, validated, and used in Armstrong (2004) to generate various results related to the performance of the active layer with changes in thermodynamic conditions and geometry is presented first. The nonporous Agglomerate Model, which is further developed, implemented, and validated in Armstrong (2004) to include, among other factors, pores, flooding, and both humidified air and humidified O2, is presented next. All models are implemented and solved using FEMAP® (2002) and a computational fluid dynamics (CFD) solver developed by Blue Ridge Numerics, Inc. (BRNI) called CFDesign® (2003). The use of these models for the discrete modeling of platinum particles is shown to be beneficial for understanding the behavior of a fuel cell. The addition of gas pores is shown to promote high current densities due to increased species transport throughout the agglomerate. Flooding is considered, and its effect on the cathode active layer is evaluated. The model takes various transport and electrochemical kinetic parameter values from the literature in order to do a parametric study showing the degree to which temperature, pressure, and geometry are crucial to overall performance. This parametric study quantifies, among a number of other things, the degree to which lower porosities for thick active layers and higher porosities for thin active layers are advantageous to fuel cell performance. Cathode active layer performance is shown not to be solely a function of catalyst surface area, but discrete catalyst placement within the agglomerate.
Cascaded Control for Regulating Soot Geometry in Vapor-Phase Axial Deposition
Authors: Jenkins Hodge E. , Nagurka Mark L.
Published: April 2008

The development of a cascaded feedback control strategy for a vapor-phase axial deposition (VAD) process is investigated in this paper. VAD is a widely used process in the creation of high purity glass for optical fiber. In previous work a soot tip surface temperature controller was developed for the VAD process to reduce the effects of core soot temperature variation on deposition, leading to a more stable process. However, this approach did not address the need to regulate and link the deposition rates of the core and clad torches. To maintain a constant distance between the core and clad deposition surfaces, it is desired to have the core soot and clad soot depositing at the same linear speed to provide a more uniform product. This paper presents the design and development of a cascaded controller strategy and process model to couple and regulate the surface temperature and deposition rates of core and clad soot. Simulations for the process and control scheme demonstrate a potential improvement in the uniformity of the core and clad soot geometry over the soot product length.
Computerized Design of Worm Gear Drives With Improved Conditions of Meshing and Bearing Contact
Authors: Gonzalez-Perez Ignacio , Fuentes Alfonso , Litvin Faydor L. , Hayasaka Kenichi , Yukishima Kenji
Published: April 2008

A new geometry of a cylindrical worm gear drive is proposed for: (i) reduction of sensitivity of the drive to errors of alignment, and (ii) observation of a favorable bearing contact. The basic ideas of new geometry are as follows: (i) the worm-gear is generated by a hob that is oversized in comparison with the worm of the drive and has a parabolic profile in normal section; (ii) the tooth surface of the worm of the drive is a conventional one. Due to deviation of the hob thread surface, the bearing contact of the worm and the worm-gear is localized. Reduction of sensitivity to misalignment and improved conditions of meshing are confirmed by application of TCA (Tooth Contact Analysis). Formation of bearing contact has been investigated by finite element method applied in 3D for more than one pair of contacting teeth. Developed ideas may be applied for various types of cylindrical worm gear drives.
Periodic Solution Analysis of a Rotor-Stator Contact Nonlinear Problem
Authors: Sarrouy E. , Thouverez F.
Published: April 2008

A typical problem encountered when studying turbo-machineries is studied: contact between a rotor and his stator. The contact is supposed to be permanent and frictionless; both rotor and stator are linked to the carter in an elastic and dissipative way. Under these modelling assumptions, nonlinear vibrations appear through the geometry of the problem when the system is excited by an out-of-balance within the rotor. Equations are written in the rotating frame in order to simplify the resultant frequency content of the dynamic quantities followed along the excitationnal frequency range. The stability and bifurcation analysis of a particular equilibrium is carried on. This first stage exhibits two Hopf bifurcation points. The associated periodic solutions are constructed and followed, using a shooting method. A specific bifurcation diagram is then established, where the incommensurate period of the solution is shown.
FEM Analysis and an Evaluation of the Sealing Performance in Flexible Box-Shape Flanged Bolted Joints With Gaskets Subjected to Internal Pressure
Authors: Sawa Toshiyuki , Kurosawa Ryo , Tatsumi Yasuaki
Published: April 2008

The contact gasket stress distributions of rectangular box-shape flange connections with compressed joint sheet gaskets subjected to internal pressure were analyzed taking account hysteresis of the gaskets using finite element method (FEM). Leakage tests were also conducted using actual rectangular box-shape flange connections with compressed joint sheet gaskets under internal pressure. By using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants between the values obtained from the present study and those by the PVRC procedure was substantial. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated.
Design of a Remote Controlled Solar Powered Boat
Authors: Huang Yuan Mao , Hush Jen Chun , Wang Kuo-Juei
Published: April 2008

This study presents design and fabrication of a remote controlled solar powered boat. Three-dimensional software Solid Works is used to construct the hull of the boat. The performance of solar cells is investigated, and an electric circuit is designed. After the conceptual design, the allocations of a DC motor, a paddle, an acceleration servo, a direction servo, solar cells and a battery are designed. The hull of the boat is fabricated by using foaming resin, all components are installed and a prototype of the remote controlled solar powered boat is fabricated. The boat is tested for speed, and the performance of the acceleration, deceleration and turning is acceptable.
Nonlinear Dynamic Analysis of Atomic Force Microscopy
Authors: Pishkenari Hossein Nejat , Behzad Mehdi , Meghdari Ali
Published: April 2008

This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as Averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for some of exciting parameters under deterministic vibration. The basin of attraction of two stable solutions is different and dependent on the exciting frequency. From this analysis the range of the frequency which will result in a unique periodic response can be obtained and used in practical experiments. Furthermore the analytical responses determined by perturbation techniques can be used to detect the parameter region where the chaotic motion is avoided. On the other hand for FM-AFM, the relation between frequency shift and the system parameters can be extracted and used for investigation of the system nonlinear behavior. The nonlinear behavior of the oscillating tip can easily explain the observed shift of frequency as a function of tip sample distance. Also in this paper we have investigated the AM-AFM system response under a random excitation. Using two different methods we have obtained the statistical properties of the tip motion. The results show that we can use the mean square value of tip motion to image the sample when the excitation signal is random.
Cost Effective Small Scale ORC Systems for Power Recovery From Low Grade Heat Sources
Authors: Leibowitz H. , Smith I. K. , Stosic N.
Published: April 2008

The growing need to recover power from low grade heat sources, has led to a review of the possibilities for producing systems for cost effective power production at outputs as little as 20-50kWe. It is shown that by utilizing the full potential of screw expanders instead of turbines, it is possible to produce Organic Rankine Cycle (ORC) systems at these outputs, which can be installed for a cost in the range of $1500 to $2000 /kWe of net output. This low capacity cost combined with the ORC's fuel-free specification results in a very favorable value proposition.
Self-Identification Experiments Using Variable Inertia Systems for Flexible Beam Structures
Authors: Senba Atsuhiko , Furuya Hiroshi
Published: April 2008

The concept of self-identification and its feasibility are experimentally investigated. The modal parameters changed multiple times by the control input of variable inertia parameter are used to obtain linear equations about unknown structural parameters to overcome the lack of modes. We derive the controllability of the modal parameters as the requested conditions for implementing self-identification using sensitivity analyses of the modal parameters with respect to the control input. Also, a criterion for the self-identification is proposed to measure the controllability. Then, the self-identification experiments are performed to examine the present method using a flexible cantilevered beam structure with variable inertia systems, which include controllable additional mass attached to the beam. As a result, the bending stiffness and mass per unit length of the test beam are accurately identified when the controllable and observable lower modes are appropriately excited by input force and their changes due to the variable inertia are accurately estimated from the combinations of a few strain gage sensors output and a cubic spline interpolation technique. The results also indicate that the identification accuracy of higher modes is affected by the accuracy of the estimated controllable mode shape, which is sensitive to the locations of sensors. As the proposed criterion is larger, the identification accuracy becomes more insensitive to the estimation error of the mode shapes.
Flow Field Analysis Inside an Annular Combustor Using CFD
Authors: Kumar V. Jyothish , Ganesan V.
Published: April 2008

Present work is concerned with the flow field analysis inside an annular combustion chamber. Geometry is modeled with all the complexities taken into account which includes swirler, atomizer, thickness of casing and liners to include real hole effects in primary and dilution holes, dome and flare part of the combustor and liner holes. There are around 790 holes in dome and 678 holes in flare part of the combustor and each of 1mm diameter. There are around 250 cooling ring holes to protect the liners. GAMBIT preprocessor is used for modeling the complex geometry. Only 20° sector is generated for analysis because of the rotational symmetry of the geometry. A parametric study has been carried out by varying the number of holes in the dome and flare part of the combustor. Diameter of the holes is varied from 1mm to 3 mm in steps of 0.2 mm. Total pressure loss is calculated across the combustor, dome and flare region for different hole diameters. A study on the effect of diameter of primary and dilution holes across the combustor is also carried out. It is found that there is no appreciable change in total pressure loss for different hole diameters of dome and flare part whereas the primary and dilution hole diameter plays an important role in determining the total pressure loss. In order to validate the code, experimental results are taken from the literature (Koutmos and McGuirk 1989) where a water model Can-Type Combustor is used for flow analysis with different mass flow rate through the swirler. The agreement between the two is reasonably satisfactory.
Parametric Optimization of WEDM of High Chromium High Carbon Die Steel Using ANN
Authors: Puri Y. M. , Deshpande N. V.
Published: April 2008

In this research, single pass cutting of HCHC (High Chromium High Carbon) die steel AISI D3 Grade has been used where material removal rate (MRR) and surface roughness (SR) are of primary importance. In general, achieving a high level cutting speed with a better surface finish is extremely difficult task because in wire cut electric discharge machining (WEDM), no particular parametric combination is expected to yield simultaneously in the best MRR and the best SR. Hence it can be considered as multi objective optimization problem. This research presents an attempt at multi objective optimization of the process parametric combinations by modeling the process using artificial neural network (ANN). A feed forward back propagation neural network based on matrix experimental design is developed to model the WEDM process. Based on the developed model, different response parameters are calculated for various input parameter setting. Finally they are compared to find out optimal combination of machining parameter setting. Electronica make EZEECUT PLUS model has been used for experimentation and a methodology has been suggested to determine the optimal combination of control parameters in WEDM. Research findings in the area of machining HCHC die steel through WEDM process will open up a new horizon and will certainly solve various challenging problems faced by the engineers and die makers in the field of modern manufacturing industry.
Effect of Pitch Chord Ratio and Side Wall Expansion Angle on Flow Through Vane Swirlers
Authors: Raj R. Thundil Karuppa , Ganesan V.
Published: April 2008

This paper is concerned with the computational study of steady flow through the vane swirlers. Swirl flow field characteristics for various pitch chord ratio (s/c) at swirler mean radius are studied for a 45° vane swirler under both sudden and gradual expansions with side-wall expansion angles of 90° and 45° respectively. In the computational study the geometry and meshing is done using pre-processor GAMBIT. Three-dimensional flow within the geometry and through the swirler has been simulated by solving the appropriate governing equations viz. conservation of mass and momentum using FLUENT code. Turbulence effects are taken care of by the Reynolds stress model and shear stress transport k-ω model for high swirls and standard k-ε model for low and medium swirls. The effect of pitch to chord ratio (s/c) on flow characteristics have been studied. The predicted results are validated with the experimental data available in the literature for s/c ratio of 1. The numerical results of axial velocity profiles downstream of the swirler at various axial planes are found to be in close agreement with the experimental results. It is found that the s/c ratio of 1 provides good turning efficiency.
Design, Modeling, and Simulation of a Piezo-MEMS Articulating Arm
Authors: Easter Clayton , O'Neal Chad B. , Selmic Rastko
Published: April 2008

Microscale actuators have been a subject of high interest in the past few years, especially for active structural control on the micro and nano scales. This includes manipulation of microparticles, two dimensional RF switching, on-chip electrical probing, and strain sensors. Previous developments for micro-actuators exhibit deflection in the vertical direction (both positive and negative). This paper presents a novel design for a cantilever piezoelectric microactuator. The design proposed is capable of actuation in the vertical as well as the horizontal direction by having a trapezoidal cross-section. This cross-section allows for the deposition of electrodes (platinum) onto sloped sidewalls, resulting in added degrees of freedom. The actuators are fabricated from link sections of traditional piezoelectric materials such as lead titanate zirconate (PZT). Currently, only single link actuators have been investigated. For the double link actuator, two sections will be connected by a joint consisting of silicon nitride, allowing for the independent actuation in the X, Y, and Z axes of each section for each specific cantilever beam. Through the utilization of voltage as the drive for the actuation, it is possible to counteract lingering oscillations in the beam resulting from initial motion. Control for this microactuator is comparable to rigid robotic structures, taking into account the modeled behavior of piezoelectric materials as well as the bending model of a trapezoidal cantilever beam. The research and development for this paper will include design, as well as dynamic modeling and simulation of a piezo-MEMS robot arm. Fabrication consists of a series of spin-casting and annealing steps to create the piezoelectric films, the polarity of which is determined by a poling process subsequent to fabrication. Conducting materials are deposited both before the PZT (bottom electrode) and after (top and sidewall electrodes), while their thicknesses will be minimalized in order to not adversely affect the beam stiffness of the piezoelectric links.