bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Characterization of Passive Fluid Mixing in Microfluidics
Authors: Svensson Erik D.
Published: November 2008

In this work we computationally characterize fluid mixing in a number of passive microfluidic mixers. Generally, in order to systematically study and characterize mixing in realistic fluid systems we (1) compute the fluid flow in the systems by solving the stationary three-dimensional Navier-Stokes equations or Stokes equations with a finite element method, and (2) compute various measures indicating the degree of mixing based on concepts from dynamical systems theory, i.e., the sensitive dependence on initial conditions and mixing variance.
Modeling and Analysis of an Ultra Light Slow Flyer With Variable Shape Control Surfaces Using Shape Memory Alloy Actuators
Authors: Alasty A. , Alemohamad S. H. , Khiabani R. H. , Khalighi Y.
Published: November 2008

Applying flexible variable shape control surfaces (wing and elevator) structures is a way to increase efficiency and maneuverability of the planes, which is recently under research. In this paper, modeling of the flight of an unmanned ultra light plane is discussed. The modeling is done based on a real ultra light plane presented recently. To increase maneuverability of the plane, flexible variable shape structures are designed for the wing and the elevator. In design procedure, having an ultra light plane is considered. The elevator and the wing are used as control surfaces for longitudinal and lateral maneuvers respectively. Shape memory alloys (SMA) are used for reshaping the flexible structures of the wing and the elevator. Because of its high power and low weight and nearly unlimited resolution, SMA is best suited as the actuator of the reshaping wing and elevator structures. In flight dynamic modeling of an ultra light plane with variable shape wing, aerodynamic coefficients are needed. Coefficients are computed using computational fluid dynamics (CFD). To determine the reshaped structures, finite element models of structures are constructed in ANSYS®. Using finite element analysis (FEA), reshaped structures are produced and transferred to FLUENT® for CFD analysis. Aerodynamic coefficients with respect to reshaped structures are computed and related to actuator forces as functions. Also, aerodynamic coefficients and their derivatives with respect to flight parameters, like the angle of attack and the angular velocities are computed. Finally, the results are combined for the complete simulation in MATLAB/Simulink®.
Inverse Problems in Non-Newtonian Electrokinetic Flows in Microchannel Networks
Authors: Zimmerman William B. , Rees Julia M. , Craven Thomas J.
Published: November 2008

A model of the electrokinetic flow of a fluid with a nonlinear viscosity of the Carreau type is simulated by finite element methods in a microchannel T-junction. The simulations accelerate the fluid from rest using the model for boundary slip velocity imposed due to a Debye double layer motion proposed by Zimmerman and MacInnes (2003). The simulations demonstrate an interval of the transient evolution of the end wall pressure profile that scales proportionally with the Reynolds number. The shape of the steady state profile is shown to be sensitive to the relaxation time scale characterizing the shear rate dependence of a Carreau fluid. Consequently, this flow regime can be taken as a paradigm viscometric flow for electrokinetic motion.
Impedance Control of a Two Degree-of-Freedom Flexible Link Manipulator Using Singular Perturbation and Sliding Mode Control Theory
Authors: Karimzadeh A. , Vossoughi G. R.
Published: November 2008

In this article, impedance control of a two link flexible link manipulators is addressed. The concept of impedance control of flexible link robots is rather new and is being addressed for the first time. Impedance Control provides a universal approach to the control of flexible robots — in both constrained and unconstrained maneuvers. The initial part of the paper concerns the use Hamilton’s principle to derive the mathematical equations governing the dynamics of joint angles, vibration of the flexible links and the constraining forces. The approximate elastic deformations are then derived by means of the Assumed-Mode-Method (AMM). Using the singular perturbation method, the dynamic of the manipulator is decomposed to the fast and the slow subsystems. The slow dynamic corresponds to the rigid manipulator and fast dynamic is due to vibrations of flexible links. The sliding mode control (SMC) theory has been used as the means to achieve the 2nd order target impedance for the slow dynamics. A controller based on state feedback is also designed to stabilize the fast dynamics. The composite controller is constructed by using the slow and fast controllers. Simulation results for a 2 DOF robot in which only the 2nd link is flexible confirm that the controller performs remarkably well under various simulation conditions.
Flow Dynamics of Vibrated Dense Granular Materials in the Presence of Ambient Gas
Authors: Soleymani Azita , Zamankhan Piroz , Yousefi Hassan , Polashenski William , Tanskanen Vesa
Published: November 2008

Results are presented from a numerical study examining the flow dynamics of condensed granular materials in the presence of an interstitial gas in a narrow gap between two concentric cylindrical buckets subjected to sinusoidal oscillation in the vertical direction of the form z = Asin(ωt), where the parameter Γ = Aω2/g exceeds a critical value, Γc, above which the system becomes fluidized. Using a recently developed expression for the stress tensor of particle phase, a set of conservation equations were derived for the particle and fluid phases interacting via an interfacial drag force. Numerical integration of the continuum equations for the granular material in buckets revealed that above Γc, granular materials may exhibit liquid-like behavior and convection can occur creating a heap similar to that previously observed experimentally.
Active Suspension of Output Feedback Robust Control Based on LMI Approach
Authors: Gu Zhiqiang , Oyadiji S. Olutunde
Published: November 2008

Traditionally automotive suspension designs have been a compromise between the three conflicting criteria of road holding, load-carrying and passenger comfort. Active and semiactive suspension control methods have been considered as ways of increasing the freedom one has to specify independently the characteristics of load carrying, handling and ride quality. Consequently, these control methods have been enthusiastically investigated in the past decades. In this paper, active suspension control based on LMIs, including H∞ control and mixed H2/H∞ synthesis has been developed in this paper. The simulation results demonstrate that robust control method can suppress disturbance from road inputs, thus improving the ride comfort and maintaining the good road handling. The mixed H2/H∞ synthesis can provide both the robustness of H∞ control and the better performance of H2 (LQR) method.
Prediction of Developing Turbulent Flow in a 90° Curved Duct Using Linear and Nonlinear Low-Re k-ε Models
Authors: Raisee M. , Alemi H. , Iacovides H.
Published: November 2008

This paper reports the outcome of applying two different low-Re number eddy-viscosity models to resolve the complex three-dimensional motion that arises in turbulent flow in a square cross-section duct passing around a 90° bend. Flow computations have been obtained using a three-dimensional, non-orthogonal flow solver. For modeling of turbulence, the Launder and Sharma low-Re k–ε model and a recently modified version of nonlinear low-Re k–ε model that have been shown to be suitable for flow and thermal predictions in re-circulating and impinging jet flows, have been employed. A bounded version of the QUICK scheme was used for the approximation of convection in all transport equations. The numerical predictions are validated through comparisons with the reported flow measurements and are used to explain how the curvature influences the flow development. The results of the present investigation indicate that the curvature induces a strong secondary flow in the curved section of the duct. The secondary motion also persists downstream of the bend, although it slowly disappears with the main stream development. At the entrance of the curved section, the curvature alters the flow development by displacing the fluid towards the convex (inner) wall. Comparisons of the predicted stream-wise and cross-stream velocity components with the measured data indicate that both turbulence models employed in the present study can produce reasonable predictions, although the non-linear model predictions are generally closer to the measurements. Both turbulence models successfully reproduce the distribution as well as the levels of the local pressure coefficient in the curved section of the duct.
A Computational Model of the Human Head and Neck for Frontal and Lateral Impacts
Authors: van Lopik David W. , Acar Memis
Published: November 2008

This paper presents the development and validation of a three-dimensional computational model of the human head and neck. The model has been produced to study the mechanics of the human cervical spine in response to automobile impacts. The complete head-neck model has been used to simulate 15g frontal and 7g lateral impacts with the resulting motion compared against response corridors derived from sled acceleration tests using human volunteers. The effect of passive and fully active muscle behaviour has been investigated and it is shown that for both impact directions the inclusion of active muscle tensioning results in closest agreement with the experimental data. Good agreement is seen for both impact directions. An analysis of the local loads in the soft-tissue components is also presented for the 15g frontal impact case.
Studies on Noise and Flow Fields in a Squirrel Cage Fan
Authors: Montazerin Nader , Damangir Abraham , Hessami Azizi Mohammad H.
Published: November 2008

There is a wide application of squirrel cage fan in heating and ventilating systems where a reduction of noise with fluid mechanics origin is of importance. This paper presents an aero-acoustic study on a squirrel-cage fan and the relation between unsteady fluid flow and the noise generated in the fan is investigated. Noise measurements in the exit channel of a fan are presented together with laser Doppler velocity measurements outside the rotor. Both measurements are Fourier transformed and important frequency contents are analyzed. Velocity measurements show that the largest fluctuations happen just after the inlet and close to the cut-off. The power spectra of velocity components near the rotor inlet and the cut off are high in comparison with other circumferential and axial positions. Blade passing frequency is dominant in noise and velocity data with a considerable volume of white band noise. It is not present at locations with no flow through the rotor. Fan performance and noise are available for different inlet geometries. An optimization of the inlet configuration changed the maximum flow rate but the sound power level was similar at the same volumetric flow regardless of the inlet shape.
Bore Polishing Wear in Diesel Engine Cylinders
Authors: Nayak Nagaraj , Lakshminarayanan P. A. , Gajendra Babu M. K. , Dani A. D.
Published: November 2008

The rate of wear of the cylinder liner is mainly a function of peak cylinder pressure, the depth of penetration of hard carbon particles ingress during abusive running conditions. The problem of wear becomes severe as the blowby past the rings and the oil consumption of an engine increases in diesel engines. In this paper, a methodology is developed to estimate the wear of liner due to bore polishing action. The wear rate is correlated with the product of gaseous load, contact stress, and sliding action of the piston surfaces. Under abnormal conditions, the shear strain due to friction exceeds the plasticity limit of the material, superficial delamination occurs at the liner surfaces. The wear model was validated on large engines running on heavy fuel at 22-bar bmep. The case study results showed that by modifying the piston profile and liner geometry, and bore polishing of the liner surfaces is reduced and the engine oil consumption rate is improved substantially.
Chaos Control in Bonhoeffer-van der Pol System Using Fuzzy Estimation
Authors: Alasty Aria , Salarieh Hassan
Published: November 2008

This paper illustrates the control of chaos using a fuzzy estimating system based on batch training and recursive least square methods for a continuous time dynamic system. The fuzzy estimator system is trained on both Ott-Geobogi-Yorke (OGY) control algorithm and Pyragas’s delayed feedback control algorithm. The system, considered for this study, is a Bonhoeffer-van der Pol (BVP) oscillator. It is found that the implemented fuzzy control system constructed on OGY algorithm results in smaller control transient response than that of the OGY control algorithm itself. The transient response of Pyragas fuzzy control does not show a significant improvement in compare to the Pyragas control itself. In general the proposed control techniques show very effective low cost energy behavior in chaos control in compare to conventional nonlinear control methods.
Elastic Analysis of Journal Bearings
Authors: Villar M. M. , Pe´rez M. M.
Published: November 2008

In this paper a numerical model is used to investigate the effect of the elasticity of the bearing in the pressure distribution in the lubricant and the stress distribution in the bearing. The lubricant film, as well as a bearing, including the lining and the backing of the insert, and the housing, are modeled using the general-purpose ANSYS®5.7 commercial Finite Element program. Results have been obtained for the pressure, radial displacement, hoop and von Mises stress distributions at the surface of the bearing, as well as for the shear stress distribution at the interface between the lining and the backing. A number of conclusions have been drawn regarding the relative significance of the steep pressure gradient at the end of the lubricated region on the hoop stresses that cause localized bending distortions at the surface of the lining. These localized bending distortions, in turn, are likely to cause fatigue failure of the lining.
Adaptive Calibration of a Capacitance Tomography System for Imaging Water Droplets Distribution
Authors: Yang W. Q. , Chondronasios A. , Nattrass S. , Nguyen V. T. , Betting M. , Ismail I. , McCann H.
Published: November 2008

A highly-sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multiphase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10−17 F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20% to 95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the droplets form liquid were detectable. It has also shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.
Combined Deterministic-Stochastic Frequency-Domain Subspace Identification for Experimental and Operational Modal Analysis
Authors: Cauberghe Bart , Guillaume Patrick , Verboven Peter , Parloo Eli , Vanlanduit Steve
Published: November 2008

Until recently frequency-domain subspace algorithms were limited to identify deterministic models from input/output measurements. In this paper, a combined deterministic-stochastic frequency-domain subspace algorithm is presented to estimate models from input/output spectra, frequency response functions or power spectra for application as experimental and operational modal analysis. The relation with time-domain subspace identification is elaborated. It is shown by both simulations and real-life test examples that the presented method outperforms traditional frequency-domain subspace methods.
Applying a Practical Method and an Out of Phase Technique to Estimate the Noise Level of Vibration Sensor
Authors: Huang Yeu-Jong , Lee Bai-Tang
Published: November 2008

The experimental and practical evaluation methods and results for vibration sensor are described in this paper. Because the vibration sensor accelerometer has the feature of low-noise electronics, the testing is performed in the basement of National Measurement Laboratory (NML), in which environmental vibration amplitude is less than 3μm/sec. First we put the sensor on a spring isolator plate with 3 Hz natural frequency and a big concrete mass with 29 Hz peak value to get the high and low frequency noise level separately. Next we mount two same-type sensors back-to-back horizontally. The output signals of the two sensors are out of phase, so we can calculate their noise level easily. Finally we use an air-bearing shaker to generate a low frequency and low amplitude vibration to verify the sensor measurement ability. The noise level of the sensor can be determined by using the practical method and an out of phase technique.
Thermal Properties of Graphite Foam: Experiments and Modeling
Authors: Yu N. , Tee C. C. , Li H.
Published: November 2008

Mesophase pitch-derived open-cell graphite foams with excellent heat transfer properties have been developed by using a relatively simple manufacturing technique [1]. The specific thermal conductivity of the graphite foam is more than seven times greater than that of copper and six times greater than that of aluminum. The present work focuses on the interactions between the effective heat transfer properties and foam microstructure, temperature, and cooling fluid properties.
Modal Characteristics of Swept Cantilevered Plates
Authors: Din Naveed A. , Oyadiji S. Olutunde
Published: November 2008

The aim of this paper is to produce modal data which can be used to synthesise assumed shapes for use in Rayleigh-Ritz approximations of the free vibrations of cantilevered swept plates. The modal data is generated via the use of the FEA technique to predict the natural frequencies and mode shapes of aluminium alloy plates of aspect ratio 2.0 and of swept angles varying from 0° to 20° in steps of 2°. The first fifty natural frequencies and mode shapes of swept cantilevered plates were calculated using ABAQUS FE programme which includes the ABAQUS/CAE pre-and post-processor. To classify each mode shape, the number of nodal lines i along the x-axis and the number of nodal lines j along the y-axis were defined. This definition worked fine for uniform rectangular plates of zero swept angles and also for the first few modes of the swept plates. But as the number of modes of the swept plates increased, this definition became difficult to apply. Similar mode shapes of the various swept angles were put into families and groups headed by the i and j definition of the uniform rectangular plate design. From this modal data, frequency charts, which showed the variation of the dimensionless natural frequencies of the swept plates with swept angle, were constructed. These charts can be used to deduce the types of modes of vibration, whether bending or torsion, of a vibrating swept plate and to synthesis accurately the assumed shapes for use in the prediction of the vibration characteristics of swept plates using the Rayleigh-Ritz approach.
Study of Turbulent Variable Density Jets With Different Asymmetric Geometries
Authors: Imine Bachir , Abidat Miloud , Imine Omar , Gazzah Hichem , Go¨kalp Iskender
Published: November 2008

In the present study, the effects of inlet jet geometry on the process of mixture with variable density have been investigated numerically. Three density ratios were considered, namely 1.0, 1.8 and 0.66 for Air-air, CH4-Air and CO2-Air mixtures respectively. The jets are produced through rectangular, elliptic and triangular tubes with aspect ratio 1.33. A second-order Reynolds stress model (RSM) is used to investigate variable density effects in asymmetric turbulent jets. Comparative studies are presented in the case of the calculations of the average variables such as the longitudinal velocity, species and the turbulent kinetic energy. The results obtained show that the asymmetric geometry noticeably enhances mixture in comparison with the axisymmetric case. Typical phenomenon of 3D jets are observed.
Delamination Buckling of Composite Cylindrical Panels Under Axial Compressive Load
Authors: Leigh Tim , Tafreshi Azam
Published: November 2008

Composite cylindrical shells and panels are widely used in aerospace structures. Delaminations within the composite structure reduce the compressive strength of laminates, and often result because of damage incurred during manufacturing and in-service use. This paper investigates the buckling behaviour of laminated cylindrical panels loaded in axial compression using the finite element method. The use of three-dimensional finite elements for predicting the delamination buckling of these structures is computationally expensive. Here the analysis has been carried out using a layerwise shell finite element based on the first-order, shear deformation theory. Contact elements were placed between the delaminated regions to avoid physical interpenetration of the elements. It is shown that through-the-thickness delamination can be modelled and analysed effectively without requiring a great deal of computing time and memory. Delamination shapes considered in this study were square and rectangular — extended longitudinally over the entire length or extended along the entire circumference of the panel. Some of the results were compared with the corresponding analytical results which were in good agreement. The most influential parameters for a given laminated panel were the size of the delamination and its through-the-thickness position. The effect of the curvature on the global buckling strength of a delaminated panel was also studied. Depending on the size and through the thickness position of delaminations, three different modes of buckling behaviour occur. The local mode occurs when the delamination is near the free surface of the laminate and the area of the delamination is large. The global mode occurs when the delamination is deeper within the laminate and has a small area. The mixed mode is a combination of global and local modes.
Practical Design Optimization of Real Life Truss Structures Constructed From Basic Modules Using the Genetic Algorithms
Authors: Dominguez-Gonzalez Aurellio , Sedaghati Ramin , Stiharu Ion
Published: November 2008

Truss structures are widely employed in the industrialized world. They appear as bridges, towers, roof supports, building exoskeletons or high technology light space structures. This paper investigates the simultaneous size, geometry and topology optimization of real life large truss structures using Genetic Algorithms (GAs) as optimizer and Finite Element Method as analyzer. In general the large truss structures are constructed from the duplication of some basic modules called bays. Thus, the final optimum design may be reached by optimizing the characteristics of the basic bays instead of optimizing the whole structure. Both single and multi-objective functions based on the mass of the structure and the maximum nodal displacement, have been considered as the cost functions. In order to have realistic optimal designs, the cross-sectional areas have been extracted from the standard profiles according to AISC codes and practical conditions are imposed to the bays. The design optimization problem is also constrained by the maximum stress, maximum slenderness ratio and the maximum and minimum cross-sectional area of the truss members. To accommodate all these constraints, two different penalty functions are proposed. The first penalty function considers the normalization of violated constraints with respect to the allowable stress or slenderness ratio. The second penalty function is a constant function, which is used to penalize the violations of the slenderness ratio. Two illustrative examples of realistic planar and space truss structures have been optimized to demonstrate the effectiveness of the proposed methodology.
Subspace Monitoring of Multivariate Dynamic Systems
Authors: Kruger Uwe , Treasure Richard J. , Dimitriadis Grigorios
Published: November 2008

In this article, the monitoring of continuous processes using linear dynamic models is presented. It is outlined that dynamic extensions to conventional multivariate statistical process control (MSPC) models may lead to the inclusion of large numbers of variables in the condition monitor. To prevent this, a new dynamic monitoring scheme, based on subspace identification, is introduced, which can (i) determine a set of state variable for describing process dynamics and (ii) produce a reduced set of variables to monitor process performance. This is demonstrated by an application study to a realistic simulation of a chemical process.
Laser Assisted Polymer Forming
Authors: Quadrini Fabrizio , Santo Loredana
Published: November 2008

In this paper the authors propose a new method for thermoplastic pellet agglomeration, the laser assisted polymer forming (LAPF). It utilises a diode laser for pellet heating and subsequently the forming in a mould. Experimental investigation was performed on thermoplastic pellets, firstly characterised by DSC. Pellet softening was studied in order to evaluate the laser-material interaction during heating. The laser power, the heating time and the pellet support were considered as experimental parameters during testing. Softening curves, together with thermal data, allow to predict the material behaviour during successive moulding. At the end, also direct pellet moulding was performed studying the effect of the moulding phase on the fabricated samples.
Fabrication of Aluminium Foam Components by Using Powder Compact Melting Method
Authors: Guarino S. , Tagliaferri V.
Published: November 2008

Recently, closed cell cellular metals have been gaining a very high interest due to their unique characteristic applications in various technology domains. They combine the advantages of a metal with the structural advantages of foam. Among these, aluminium foams have created a great interest due to their light weight structure and their various applications in the automotive, aerospace and allied industries. Aluminium foam possesses high stiffness and low density, it has good energy-absorbing properties making it good for crash-protection and packaging and it has attractive heat-transfer properties that permit to use these materials to cool electronic equipment and as heat exchangers in engines. However, its manufacturing techniques and characterization methods need more attention. The inadequate knowledge on the physical phenomena governing the foaming process does not allow to obtain products with repeatable characteristics. In this paper aluminium foams in various fabrication components were produced by applying the powder compact melting method. In particular metal powders (AlSi7) and powdered gas-releasing blowing agents (TiH2) were mixed and subsequently pressed to obtain a foamable precursor material. The resulting precursor was then foamed by heating it up to above its melting point. Experimental tests were performed to study the fabrication of aluminum foam components and with the extent of optimize the pressing parameters of the foamable precursor material, the foaming temperature and the heating rate during foaming. It was studied the effects of geometrical discontinuities in the mould (such as holes, restrictions, etc) on the evolution and on the morphology of metal foams.
Numerical Simulation of Piezoelectric Sensor Used in a New Pedestrian Protection System
Authors: Capitani Renzo , Iacomelli Tommaso , Gobetto Enrico
Published: November 2008

In recent years, pedestrians have been involved in many accidents. Statistics show that in Europe pedestrians are involved in 12% of the accidents and 20% of road users who lose their life in accidents are pedestrians. Authorities and automobile manufacturers are interested to reduce the physical damages of these users. The EU requires a very accurate design of new car front-end, because this is the first part involved in the car-to-pedestrian impact. Some EU organisations as EEVC (European Enhanced Vehicle-Safety Committee- Working Group 17) and ACEA (Association des Constructeurs Europeens d’Automobiles) have decided the directives on the design of the new car front-end. These documents settle on the experimental methods and the biomechanical parameters that have to be considered combining the front-end aggressiveness with the crash test dummies damages. Moreover, many car and system manufacturers are studying new pedestrian protection systems as the active hood that raises instantly when a pedestrian is hit: a sensor system placed in the vehicle’s front bumper sends a signal a two steel pistons below which lift the rear part of the hood making the pedestrian’s head hit a deformable and flexible surface instead of a hard and rigid one. These systems will help car manufacturers to meet the new EU test requirements that the European car manufacturers accepted in 2001 and that will become effective in July 2005. This paper describes an activity on car-to-pedestrian impact carried on by the Universita` degli Studi di Firenze in co-operation with Centro Ricerche FIAT. This activity concerns the study of legform FEM model for LS-Dyna software and the numeric simulation of a sensor system placed in the vehicle’s front bumper. The sensors are piezoelectric stripes stuck on the bumper according to opportune geometries. These sensors were characterised through experimental analysis changing deflection and impact speed; the relationship between the numeric parameters and the electric signal was determined working on easy tests. It was subsequently simulated the impact between the bumper and a legform FEM model developed by Universita` degli Studi di Firenze working on LS-Dyna software. The legform model respect the structural characteristics required by EEVC WG17 report. The legform model was validated by experimental analysis carried on at Centro Sicurezza FIAT AUTO. Thanks to simulations it has been possible to optimise the position of the sensors on the bumper and also to judge the minimum number of sensors, which can distinguish between the different impacts.
Inverse Kinematics Analysis and Workspace of a New 3-RRRR Parallel Manipulator
Authors: Bahrami Mohsen , Moghaddam Iman Ebrahimi
Published: November 2008

This paper presents a new 3-RRRR parallel manipulator. In the proposed mechanism, the revolute actuators are fixed to the base, which leads to a reduction of the inertia of the moving links and hence makes it attractive, particularly when high-speed motions are required and electric actuation is considered. This manipulator can be used in robotic applications involving the positioning and orientation of a rigid body in the space with high-speed, accuracy and high stiffness or as a simulator or others high-precision or high-speed devices. After introducing the mechanism, inverse kinematics analysis is presented. By the virtue of complexity of analytic solution, an algorithm is utilized which can numerically find possible of solutions and choose the one with applicable configuration. Then the workspace of manipulator is obtained by means of proposed numerical solution.
Vibration Analysis of Axially Loaded Bridges Traversed by Accelerating Vehicles With Passenger Dynamics
Authors: Hassanpour Asl P. , Mehdigholi H. , Esmailzadeh E.
Published: November 2008

An investigation into the dynamics of vehicle-passenger-structure-induced vibration of suspension bridges traversed by accelerating vehicles is carried out. The vehicle including the driver and passengers is modeled as a half-car planer model with six degrees-of-freedom. In addition, the stiffness of compliant bushings at the connecting points of the shock absorbers to the body is considered. The bridge is assumed to obey the Timoshenko beam theory with axial load and arbitrary conventional boundary conditions. The roughness of the bridge is assumed as a differentiable function of location. Due to continuously moving the location of the variable loads on the bridge, and in the presence of damping force, the governing differential equations become complicated. The numerical simulations presented here are for the case of a vehicle traveling at a constant acceleration on a uniform bridge with rough surface and simply supported end conditions. The relationship between the bridge vibration characteristics, bridge roughness, and the vehicle speed and acceleration is rendered, which yields into search for a particular acceleration and speed that determines the maximum value of the dynamic deflection and the bending moment of the bridge. Results obtained from the Timoshenko beam theory are compared with those from the Euler-Bernoulli beam for which full agreements are found. Finally, the maximum deflection of the beam under moving loads is compared with that of the case with static loading.
Nanoscale Vibrational Analysis of an Embedded Multi-Layered Graphene Sheet
Authors: Behfar K. , Naghdabadi R. , Vafai A. , Estekanchi H. E.
Published: November 2008

In this paper, nanoscale vibrational analysis of a multilayered graphene sheet embedded in an elastic medium is investigated and the corresponding resonant modes and frequencies are determined. It is known that the elastic moduli of a graphene sheet in two orientations x, y are different, so the graphene sheet is assumed to be a general form of an orthotropic plate. The orthotropic sheets stacking at the top of each other bond with carbon-carbon van der Waals forces, also the whole multi-layered graphene sheet is influenced by polymer-carbon van der Waals forces from the surrounding elastic medium.
Influence of Water Behavior in the Gas Diffusion Layer on the Performance of PEMFC
Authors: Park Gu-Gon , Sohn Young-Jun , Yim Sung-Dae , Yang Tae-Hyun , Yoon Young-Gi , Lee Won-Yong , Kim Chang-Soo
Published: November 2008

The affect of water behavior on the performance of the polymer electrolyte membrane fuel cell (PEMFC) was investigated experimentally. To understand the water transportation phenomena systematically, the gas diffusion layers were divided into two parts: the gas diffusion medium (GDM) and the micro-layer (ML). In this work, different Teflon (PTFE) contents in the GDM were intensively investigated under various single cell operation conditions. Current-Voltage (I-V) performance curves of single cells were compared and analyzed with respect to water transportation in the GDM. Through the results of this work, the dominant driving forces of the water transportation in the gas diffusion layer were determined which aids in designing the gas diffusion layers.
Numerical Analysis of Water Transport in PEM Fuel Cell Membranes Using a Phenomenological Model
Authors: Sui P. C. , Djilali N.
Published: November 2008

A numerical investigation on the water transport across the membrane of a proton exchange membrane fuel cell is carried out to gain insight into water management issues, which are crucial to the efficient operation of such fuel cells. The transport equation of water content based on a phenomenological model, which includes an electro-osmotic drag term and a diffusion term, is solved using the finite volume method for a 1-D configuration with the assumption of a uniform temperature distribution. Transport properties including the drag coefficient and diffusion coefficient of water in the membrane and the ionic conductivity of the membrane are expressed as functions of water content and temperature. The effects on the water flux across the membrane and on overall membrane protonic conductivity due to variations of these properties are studied. The numerical results show that water transport in the membrane is mainly determined by the relative strength of electro-osmotic drag and diffusion, which are affected by operating conditions such as current density and relative humidity at the membrane surface, and design parameters such as membrane thickness and membrane material. Computed water fluxes for different humidity boundary conditions indicate that for a thick membrane, e.g. Nafion 117, electro-osmotic drag dominates transport over a wide range of operating conditions, whereas for a thin membrane, e.g. Nafion 112, diffusion of water becomes equally important under certain conditions. Implications of the one-dimensional investigation on comprehensive CFD based modelling of proton exchange membrane fuel cell are also discussed.
AC Impedance Investigation of Flooding in Micro Flow Channels for Fuel Cells
Authors: Cha Suk Won , O’Hayre Ryan , Prinz F. B.
Published: November 2008

The paper presents a study on the transport phenomena related to gas flow through fuel cell micro-channels, specifically the impact of dimensional scale on the order of 100 microns and below. The use of structural photopolymer (SU-8) enabled the direct fabrication of functional fuel cell micro-channels. Previous experimental observation has revealed that if flow channels are too small, they may reduce the performance of fuel due to flooding (Cha et al., 2003). For further investigation, AC Impedance technique has been employed to measure the mass transfer resistance. The result confirmed that in smaller channels, mass transportation resistance increases due to the flooding.
Performance of Anode-Supported SOFC Single Cells Using Thin Electrolyte of YSZ and ScSZ at Intermediate Temperatures
Authors: Yoo Young-Sung , Seo Hai-Kyung , Ahn Kyo-Sang , Oh Je-Myung , Bae Joongmyeon
Published: November 2008

Present results on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused to obtain higher performance of single cell at lower operating temperature, especially with planar type. In order to develop a 1 kW-class SOFC system for Residential Power Generation (RPG) application that can be operated at intermediate temperatures, we have developed an anode-supported and planar type SOFC stack using cost-effective interconnects such as ferritic stainless steels. To improve electrical performance of the anode-supported SOFC, cells with alternative electrode or thin electrolyte layer of YSZ and ScSZ, respectively, were fabricated by slurry coating and their performances were investigated. Mixtures of NiO and 8YSZ powders were pressed into rectangular plates, which were pre-sintered at 1400°C for 1 h. Then the 8YSZ (8mol%Y2O3+ZrO2) or 10ScSZ (10mol%Sc2O3+1 mol%CeO2+ZrO2) electrolytes were coated by slurry coating method on the upper side of anode substrate and cofired at 1550 or 1500°C for an hour. Thereafter, composite cathode pastes of LSM (La0.7Sr0.2MnO3) or LSCF ((La0.6Sr0.4)(Co0.2Fe0.8)O3 ) were screen-printed on thin electrolytes and heat-treated at 1100°C for 2 h. The final size of anode-supported single cell sintered was about 5 × 5 cm2, and the thickness of the electrolyte and the cathode layer was about 20 μm and 30 μm, respectively. The I-V and AC impedance characteristics of these single cells were evaluated at intermediate temperature (650 ∼ 750°C) using hydrogen gas as a fuel. The maximum power density of anode-supported cell was 0.4 ∼ 1.7 W/cm2 at 750°C and 0.12 ∼ 0.55 W/cm2 at 650°C depending on the composition and microstructure of electrolyte/electrodes.
Microscopic Observations of SOFC Anodes Under Operation With Hydrocarbon Fuels
Authors: Kawada Tatsuya , Yashiro Keiji , Taura Tomoaki , Takeda Kenichiro , Kaimai Atsushi , Matsumoto Hiroshige , Mizusaki Junichiro , Yugami H.
Published: November 2008

Carbon deposition on a SOFC anode was investigated under direct hydrocarbon fueling condition. Microscopic behaviors were observed with a newly designed sample holder that enabled in-situ observation of an electrode in operation under controlled atmosphere at elevated temperatures. The preferential carbon deposition site, the structure of the deposited carbon, and the chemical or electrochemical re-oxidation processes were investigated with an optical microscope combined with a laser Raman microscope. Color and morphology change of the electrode surface was recorded with a CCD camera, and the deposited materials were identified with a laser Raman microscope. A nickel micro grid was used as a model electrode of a well-defined microstructure. When the cell was kept at an open circuit condition in methane, carbon started to deposit on the surface of Ni grid electrode. The deposition of carbon was clearly observed as the change in the reflection on the nickel surface by optical microscope as well as by the appearance of the specific peak at ∼ 1560 cm−1 in Raman spectroscopy. The deposited carbon was in the form of graphite on the nickel grid electrode. The carbon coverage on the surface was not uniform but varied from grain to grain. When a certain anodic overpotential (e.g. 200 mV) was applied to the electrode, the carbon disappeared gradually from the edge of the electrode i.e. from the electrode/electrolyte boundary where oxygen was supplied electrochemically. It is the first in-situ observation of the electrochemical carbon oxidation in a real operation condition.
Technology Status and Design Overview of a Hybrid Fuel Cell System for a Motorcycle
Authors: English Nathan J. , Shah Ramesh K.
Published: November 2008

The global development of fuel cell based propulsion has emphasized larger vehicles, with most manufacturers demonstrating a car, van or truck. However, the transportation market in many countries is dominated by smaller two and three wheeled vehicles. A fuel cell motorcycle could replace two stroke scooters that proliferate emissions, as well as, their electric counterparts that require long recharges for short ranges, and also four stroke motorcycles. This paper is a review and assessment of literature relating to the design and analysis of hybrid electric fuel cell motorcycle engines. The engine design is intended for a specific demonstration motorcycle, but should be able to scale down to a scooter size, or be adapted to work in other small vehicles. The proton exchange membrane fuel cell system utilizes an ambient air blower, pure hyrogen storage in metal hydrides, a control system, active liquid cooling, a radiator, power conditioning and water management systems.
A Stack Design for Portable Direct Methanol Fuel Cell Based on the Newly Developed Heterogeneous Composite Bipolar Plate
Authors: Chen Long-Jeng , Lee Ming-San
Published: November 2008

There are several problems associated with the marketing of portable direct methanol fuel cell (DMFC). The most critical one is how to supply fuel to all cells without supplementary devices. It requires a serial connection of 12, 24 and 48 cells to acquire enough voltage to operate a cellular phone, a digital video camera and a personal computer, respectively. How can methanol be supplied to all these cells if the conventional stacking method is adopted? Supplementary devices such as pumps, fans, and complex piping system must be used and, as a result, the word “portable” no longer applies. New stacking approach must be developed before portable DMFC can be put onto the market. The idea behind the promising “banded” type stack is simple. Problems only come when one tries to implement it. What is the actual device that can collect and transport those electrons between electrodes with minimum electrical resistance and, yet, be able to survive in the acidic environment inside the cell and, more importantly, not to harm the membrane electrode assembly (MEA)? Currently, there is none with reasonable cost. The new heterogeneous composite bipolar plate developed in our laboratory is composed of rows of carbon fiber bunches and plastic main plate body. The carbon fiber bunches are perpendicular to and penetrate through the main plate body. Besides being light, better performance, and low cost, the new plate has a unique property. Since the main plate is an insulator, the rows of fiber bunches may be arranged to be electrically independent with each other. When MEA is made into banded structure and with each band corresponding to one row of fiber bunch on the plate, all bands will function as different cells and higher voltage may be acquired in a smaller volume. Thus, just two bipolar plates (“unipolar” should be called in this case) with one “banded” MEA in between can form a very simple multi-cell stack. The serial connection may be done outside the cell and, therefore, low cost metal such as copper, which has great electrical conductibility but is harmful to MEA, may be used to transport the electrons which are conveyed outside the cell through carbon fiber bunches in the first place. The fact that it has only one anode chamber and one cathode chamber eliminates the difficult problem of distributing fuel sufficiently to all cells without supplementary devices. As a matter of fact, the anode chamber may be used as a methanol storage tank to further reduce the volume. The structure of the new stack design presented in this paper is simple, durable and low cost. It holds the key to the success in marketing the portable DMFC.
A Simple Thermal Model of PEM Fuel Cell Stacks
Authors: Wetton B. , Promislow K. , C¸ag˘lar A.
Published: November 2008

A simple model is developed that determines the temperature distribution through a unit fuel cell with straight flow channels, in steady state operation. Using the large aspect ratio of the typical fuel cell geometry, the thermal model approximately decouples cross-plane thermal transport at each channel location. Using the fact that in-plane thermal conductivities are much larger than through-plane in typical bipolar plate construction, it is possible to further approximate the cross-plane thermal transport with a simple, one-dimensional model. We then consider the thermal coupling of several unit cells connected in series. In this way, we can simulate the effect of an anomalously hot cell in a stack environment. We take as inputs to the model the cell voltage and local current density, membrane resistance and condensation rates from a previously developed model. The thermal model outputs the average coolant temperature and the temperature distribution through the bipolar plates and membrane electrode assembly at each location down the channel. Although we are aware that there are significant coupling effects between the thermal distribution and performance, this is not taken into account in this study.
Analysis of a 3 kW PEM Fuel Cell Stack Developed by ITRI
Authors: Tsai M. H. , Yan Y. Y. , Chu H. S. , Shyu R. J. , Tsau F.
Published: November 2008

A 3kW PEMFC power generation system is developed by Energy and Resources Laboratories in 2002. This system integrates hydrogen storage, fuel reformer, power conversion, hot water tank as well as a 3kW PEMFC stack. The power generation efficiency at 30% and total energy efficiency with hot water recovery at 67% are designed. The stack is key component of this system, and its performance is tested and analyzed before it is integrated into the system. This paper presents its performance in I-V polarization curves with controlling parameters such as fuel cell operating temperature, air humidity, hydrogen humidity and stoichimetric ratio of air. Detailed discussions are given for the effect of each parameter on stack’s performance.