bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of Multi-Parameter Models by Least Squares and Adaptive Filters
Authors: Emery A. F.
Published: May 2008

Parameter estimation is based upon a comparison of predicted deterministic model responses to data. The models are often numerical, e.g., finite volume, with intrinsic inaccuracies. In addition, the models typically assume a full knowledge of the physical processes. By using the concept of state variables and employing the Kalman filter approach it is possible to include undetermined effects in the model. This paper describes such an approach to the estimation of thermal conductivity in a transiently heated and cooled one dimensional system and shows that it leads to a resolution of questions about the time behavior of the residuals previously observed in an estimation based upon the least squares analysis.
An Inverse Algorithm to Estimate Spatially Varying Thermal Contact Resistance
Authors: Divo Eduardo , Kassab Alain J. , Gill Jennifer
Published: May 2008

Characterization of the thermal contact resistance is important in modeling of multi-component thermal systems which feature mechanically mated surfaces. Thermal resistance is phenomenologically quite complex and depends on many parameters including surface characteristics of the interfacial region and contact pressure. In general, the contact resistance varies as a function of pressure and is non-uniform along the interface. An inverse problem is formulated to estimate the variation of the contact resistance. A two-dimensional model is considered where the contact resistance is sought along the contact line at the interface between two regions. Temperature measured at discrete locations using embedded sensors placed in proximity to the interface provides the additional information required to solve the inverse problem. Given current estimates of the contact resistance as a function of position along the interface, a forward problem is solved, and a quadratic objective function is formulated to evaluate the difference between predicted temperatures at the sensors and those measured. A genetic algorithm is used to minimize the objective function and obtain the best estimate of the contact resistance. A boundary element method is used to solve the forward temperature field problem. Numerical simulations are carried out to demonstrate the approach. Random noise is used to simulate the effect of input uncertainties in measured temperatures at the sensors.
Estimation of the Thermal Properties and Interface Conditions of Heterogeneous Materials
Authors: Loulou Tahar , Scott Elaine P. , Vick Brian
Published: May 2008

The conjugate gradient method using vectorial descent parameters is used to solve the inverse problem of simultaneously estimating one boundary condition and one thermo-physical property of an heterogeneous material. The advantage of the conjugate gradient method lies in that no a priori information is needed on the variation of the unknown quantities. The heterogeneous material model under consideration consists of a matrix in imperfect contact with embedded separated particles. The first unknown of interest in this inverse problem is the constant coupling parameter Ψ which characterizes the thermal contact (conductance) behavior between the matrix and the particles. The second unknown is the time dependent applied heat flux on one external side of the matrix. As a result, this problem is concerned with a combined parameter and function estimation at the same time. Thus two descent parameters, each one corresponding to each unknown function parameter, are derived and used in the iterative process. The developed inverse analysis is based on the transient temperature measurements taken from some sensors implanted inside the matrix only during the process of heating. Several numerical test cases were performed and show that the developed method provides an accurate estimation of thermo-physical properties and boundary condition in a very short practical time.
Miniaturized Thermoelectric Cooler
Authors: da Silva Luciana W. , Kaviany Massoud
Published: May 2008

Vapor-deposited bismuth telluride (n-type) and antimony telluride (p-type) films are used in a micro, column-type, patterned thermoelectric cooler. The optimum number of thermoelectric pairs and operating current are predicted. Such devices contain a number of metal/thermoelectric and metal/elecrical-insulator interfaces. In the analysis, various interfacial resistances (phonon and electron boundary resistances and thermal and electrical contact resistances) have been included. The boundary resistances cause a reduction in the thermal conductivity (desirable) and a reduction in the Seebeck coefficient (undesirable) of the thermoelectric elements. The contact resistances reduce the overall device performance. In the fabrication, the stoichiometry of the deposited thermoelectric films, the patterned film deposition, and the selection of the conducting connectors, are discussed. The thermoelectric films are about 4 μm thick and are deposited on patterned platinum (first trial layer for connectors), which are in turn deposited on oxide coated silicon wafers. The top, suspended connectors that close the electrical circuit are bonded to the surface to be cooled. The non-uniformity of the composition in the thermoelectric films influences the measured Seebeck coefficients. The analysis shows that a coefficient of performance of 0.38 is obtainable for a wireless micro sensor application.
Opto-Microactuator With Low-Thermal-Conductivity Material by Laser Heating
Authors: Ota Masahiro , Noguchi Atsunobu
Published: May 2008

A laser opto-microactuator is proposed in this paper. The effects of the thermal-conductivity of actuator materials on rotational phenomena are discussed. The actuator with 4 flat blades made of aluminum or Pyrex glass plate was installed in a vacuum chamber. By molecular gas dynamics effects, the actuator is rotated with the irradiation of argon ion laser beam. The blade surfaces of the actuator were coated by carbon black powder for absorbing laser beam power and heating the surfaces. Just after irradiating one blade surface of the actuator by the laser, the macroscopic gas flow is induced around the actuator at non-zero Knudsen number. By the reaction of the induced flow the actuator can rotate. This is the molecular gas dynamics effects (1)(2). The rotational rate of the actuator with Pyrex glass blades is faster than that of the actuator with aluminum blades. Because Pyrex glass has about 200 times or more of lower thermal-conductivity than that of the aluminum, then Pyrex glass blades maintain a lager temperature difference between front and rear surfaces and a large molecular gas dynamics effects. Also irradiating to the glass surface, Pyrex glass rotor can rotate counter-clock-wise of irradiating to carbon-coated surface.
Thermal Measurements in Rectangular Microchannels
Authors: Popescu Aristotel , Welty James R. , Pfund David , Rector David
Published: May 2008

This paper reports on an experimental study of heat transfer in high aspect ratio (width/depth), rectangular micro-channels. A single channel with width of 10 μm was cut into polycarbonate spacers of various thicknesses, resulting in channel depths of 128 μm, 263 μm and 521 μm. Heat transfer experiments were performed with a constant heat flux boundary condition applied at the surface of the channel. Experiments conducted for refrigerant R-124 working fluid in the range Re = 300 − 900 and Pr = 3.6 − 3.8 showed small or no departure from macro-scale predictions for channels with hydraulic diameters larger than 500 μm. Results for the 80:1 aspect ratio channel showed a significant departure from theoretical predictions. Experimental values of local Nusselt numbers were approximately 25 percent lower than predicted using macro-scale theory.
Periodic Heating of an Anisotropic Superlattice With Thermal Boundary Resistance
Authors: Foley Jason R. , Avedisian C. Thomas
Published: May 2008

The conduction of heat from a modulated heat source of finite size is analyzed for a semi-infinite solid in contact with the adjacent gas. The solid is a semi-infinite layered composite structure consisting of a superlattice (of thickness Δ) grown on a substrate. Using partitioned matrices that arise naturally from boundary conditions, a closed form solution for the temperature distribution in the solid and gas is found for the limit of conduction-dominated heat transport in the gas. The general case is analyzed in which each layer of a superlattice can have different anisotropic thermal conductivities as well as different thermal boundary resistances between the individual layers due to the growth process. Limits of this most general case are discussed in which all “A” and all “B” layers are themselves the same. The temperature field that arises from the general problem is used to compute probe beam deflections in the gas for the photothermal deflection spectroscopy (PDS) technique for measuring the thermal conductivity. Results are presented to show how probe beam deflection components, and the effective properties of the superlattice, are influenced by the number of periods of the superlattice, thermal properties of the superlattice layers, and the presence or absence of a thermal boundary resistance between the layers.
A New Approach to the Modeling of MDOF Vehicles Traversing Rough Surfaces
Authors: Pesterev Alexander V. , Bergman Lawrence A. , Tan Chin An
Published: May 2008

A technique is developed to predict the dynamic contact forces arising after passing road surface irregularities by a vehicle modeled as an undamped multiple-degrees-of-freedom (MDOF) system. An MDOF system moving along an uneven profile is decomposed into an aggregate of independent oscillators in the modal space, such that the response of each oscillator can be calculated independently. The technique developed is applied to the calculation of the coefficients of the harmonic components of the contact forces arising after the passage of a “cosine” pothole. The application of the technique to other problems is also discussed. One interesting phenomenon reported in the DIVINE project [1], regarding the replacement of a steel suspension by an air suspension resulted in increase of the maximum response of short-span bridges is explained by applying the technique suggested. The discussion is amply illustrated by examples of the application of the technique to the calculation of the tire forces due to a pothole for two simple—quarter-car and half-car—vehicle models.
Constitutive Modeling of Asphalt Bound Granular Materials: Applications to Sand Asphalt
Authors: Murali Krishnan J. , Rajagopal K. R.
Published: May 2008

In the earlier paper, we developed constitutive relations for two kinds of hot mix asphalt, viz., asphalt concrete and sand asphalt using the framework of materials with multiple natural configurations. In the present paper, we apply the framework that we developed for sand asphalt to study compressive creep experiments. Experimental studies of Wood and Goetz (1959) are used to compare with the predictions of the model.
Clustering, Jamming and Segregation in Cohesive Granular Materials
Authors: Samadani Azadeh , Blair Daniel L. , Kudrolli A.
Published: May 2008

We present a series of experiments to investigate the stability, flow and segregation when liquid bridges or magnetic attraction forces between grains are present. Quantitative data is obtained by high speed and high resolution imaging. First, we measure the angle of repose of a granular pile formed by pouring wet grains in to a quasi-two dimensional silo and compare them to existing models. Second, we measure the size separation of bi-disperse grains as a function of size ratio and viscosity of the liquid. Finally, we introduce a vibro-fluidized system of magnetized particles to study the effect of cohesive forces and inelastic collisions on the formation of clusters and velocity distributions.
Robotic Highway Safety Markers
Authors: Farritor Shane M. , Rentschler Mark E.
Published: May 2008

Proper traffic control is critical in highway work zone safety. Traffic control devices such as signs, barricades, cones, and plastic safety barrels are often used. Accidents can occur because of improper work zone design, improper work zone housekeeping, and driver negligence. One solution is to automate safety devices. This paper presents a mobile safety barrel robot. The Robotic Safety Barrels are the first elements of a team of Robotic Safety Markers (RSM) that includes signs, cones, and possibly barricades and arrestors. To be practical the system must be reliable and have a low per robot cost. A robot that malfunctions could enter traffic and create a significant hazard. Also, multiple safety markers are used and barrels are often struck by vehicles. Safety markers with a high replacement cost are not practical. This paper describes the motivation for the robotic safety marker system and how it could improve work zone safety. The design of three robot prototypes is presented. A control architecture is discussed that has been implemented in simulation and partially tested on the prototype robots.
Mechatronic Redesign of Slider Crank Mechanism
Authors: Nagchaudhrui Abhijit
Published: May 2008

Mechatronic design efforts have been and continue to be heavily investigated in the development of robotic manipulator arms. However, little effort has been devoted to mechatronic redesign of traditional two-dimensional mechanisms which mechanical engineers get exposure to when they study subjects such as kinematics and mechanism design. In this paper a feasibility study for controlling the motion of the popular slider crank mechanism with appropriate sensing and actuation is elaborated. The results indicate that a variety of motion profiles can be derived from the same mechanism without involving any mechanical redesign. Many of the control approaches that have been heavily investigated in the field of robotics are readily applicable to such mechanisms. The synergistic combination of mechanical design, soft computing, sensing, instrumentation, and control is likely to bring about unprecedented versatility and performance levels in the hardware realization of machines based on these mechanisms.
A New Deterministic Method for Clearance Influence Analysis in Spatial Mechanisms
Authors: Parenti-Castelli Vincenzo , Venanzi Stefano
Published: May 2008

This paper focuses on spatial mechanisms with clearance-affected joints. After the review of several existing methods for the evaluation of clearance effects, a new original method is provided. The new method is shown to be more flexible and complete than the previous ones in the evaluation of clearance influence. More flexible because it allows the use of a generic model for the kinematic pairs. More complete because it can be applied to both open and close chain mechanisms loaded on a generic link.
A Convective Description of Flexible Robot Dynamics
Authors: Franitza Daniel
Published: May 2008

This paper describes a theory for dynamics simulation of non-linear elastically deformable mechanisms as a basis for compliant manipulators. The description of the mechanical structure based on local coordinates in a convective metric for one-dimensional structures is introduced. Besides the quasi-static case, loads related to mass inertial terms are taken into consideration. This changes the original first order set of linear differential equations into non-linear second order partial differential equations. Some numerical aspects for the generation of a solution for the initial boundary value problem described are discussed.
Constitutive Modeling of Asphalt Bound Granular Materials: Theoretical Background
Authors: Murali Krishnan J. , Rajagopal K. R.
Published: May 2008

Different kinds of hot mix asphalt mixtures are used in highway and runway constructions. Each of these mixtures cater to specific needs and differ from each other in the type and percentage of aggregates and asphalt used, and their response can be markedly different. Constitutive models used in the literature do not differentiate between these different kinds of mixtures and use models which treat them as if they are one and the same. In this study, we propose constitutive models for two different kinds of hot mix asphalt, viz., asphalt concrete and sand asphalt. We use a framework for materials that possess multiple natural configurations for deriving the constitutive equations. While asphalt concrete is modeled as a two constituent mixture, sand asphalt is modeled as a single constituent mixture due to the peculiarity in its makeup. In this study, we present a unified approach for deriving models for these different kind of mixtures. In a companion paper, we compare the predictions of the model for a compressive creep test with available experimental results.
Multiphase Flows Through Poro-Elastic Media: A Continuum Model
Authors: Ahmadi Goodarz , Mazaheri Ali Reza , Smith Duane H.
Published: May 2008

Based on the basic balance laws and the second law of thermodynamics, a model for multiphase fluid flows through poro-elastic media is presented. The basic conservation laws. Including the balance of phasic equilibrated forces are are described. Based on the thermodynamics of the multiphase mixture, appropriate constitutive equations are formulated. It is shown that the present theory leads to the extension of Darcy’s law and contains, as its special case, Biot’s (1957) theory of saturated poro-elastic media. The special case of gas-liquid flows in porous media is discussed.
A Simple Model for the Effective Thermal Conductivity of a Particulate Mixture
Authors: Massoudi Mehrdad , Phuoc Tran X.
Published: May 2008

When a coal stockpile is stored in the presence of air, slow oxidation of the carbonaceous materials occurs and heat is released. If the rate of heat generation within the stockpile is greater than the rate of heat dissipation and transportation to the external environment, the self-heating of the coal stockpile ensues. The self-heating of coal stockpiles has a long history of posing significant problems to coal producers because it lowers the quality of coal and may result in hazardous thermal runaway. Precise prediction of the self-heating process is, therefore, necessary in order to identify and evaluate control measures and strategies for safe coal mining, storage and transportation. Such a prediction requires an accurate estimate of the various processes associated with the self-heating which are impossible unless the appropriate phenomenological coefficients are known. This note is to present a simple approach to determine the effective thermal conductivity of a granular porous medium such as a coal stockpile.
Maximum Entropy Methods in the Mechanics of Quasi-Static Deformation of Granular Materials
Authors: Kruyt N. P. , Rothenburg L.
Published: May 2008

In statistical physics of dilute gases maximum entropy methods are widely used for theoretical predictions of macroscopic quantities in terms of microscopic quantities. In this study an analogous approach to the mechanics of quasi-static deformation of granular materials is proposed. The reasoning is presented that leads to the definition of an entropy that is appropriate to quasi-static deformation of granular materials. This entropy is formulated in terms of contact quantities, since contacts constitute the relevant microscopic level for granular materials that consist of semirigid particles. The proposed maximum entropy approach is then applied to two cases. The first case deals with the probability density functions of contact forces in a two-dimensional assembly with frictional contacts under prescribed hydrostatic stress. The second case deals with the elastic behaviour of two-dimensional assemblies of non-rotating particles with bonded contacts. For both cases the probability density functions of contact forces are determined from the proposed maximum entropy method, under the constraints appropriate to the case. These constraints form the macroscopic information available about the system. With the probability density functions for contact forces thus determined, theoretical predictions of macroscopic quantities can be made. These theoretical predictions are then compared with results obtained from two-dimensional Discrete Element simulations and from experiments.
Analysis of the Elasto-Plastic Response of a Polygonal Packing
Authors: Marroqui´n Fernando Alonso , Herrmann Hans , Luding Stefan
Published: May 2008

We investigate the constitutive response of two-dimensional packed samples of polygons using molecular dynamics simulation. The incremental elasto-plastic response is examined in the pre-failure regime. Besides the Young modulus and the Poisson ratio, an additional parameter must be included, which takes into account the anisotropy of the elastic response. The plastic deformations are described by the introduction of the yield and the flow directions. These directions do not agree, which reproduces the non-associated feature of realistic soils. In order to detect the yield surface, different loading-unloading-reloading tests were performed. During the reload path, it is found that the yielding develops continuously with the amplitude of loading, which does not allow to identify a purely elastic regime.
A Comparative Study of the Response of Double Shearing and Hypoplastic Models
Authors: Zhu Huaning , Mehrabadi Morteza M. , Massoudi Mehrdad
Published: May 2008

The principal objective of this paper is to compare the mechanical response of a double shearing model with that of a hypoplastic model under biaxial compression and under cyclic shear loading. As the origins and nature of these two models are completely different, it is interesting to compare the predictions of these two models. The constitutive relations of the double shearing and the hypoplastic models are implemented in the finite element program ABACUS/Explicit. It is found that the hypoplastic and the double shearing constitutive models both show strong capability in capturing the essential behavior of granular materials. In particular, under the condition of non-cyclic loading, the stress ratio and void ratio predictions of the double shearing and the hypoplastic models are relatively close, while under the condition of cyclic loading, the predictions of these models are quite different. It is important to note that in the double shearing model employed in this comparison the shear rates on the two slip systems are assumed to be equal. Hence, the conclusions derived in this comparison pertain only to this particular double shearing model. Similarly, the hypoplasticity model considered here is that proposed by Wu, et al. [30] and the conclusions reached here pertain only to this particular hypoplasticity model.
New Developments in ‘Rapid Granular Flows’
Authors: Goldhirsch Isaac
Published: May 2008

The recent decade or so has witnessed much progress in the field of granular matter in general and granular gases (or rapid granular flows) in particular. On the theoretical side, there have been systematic developments of hydrodynamic models for granular gases based on the Chapman-Enskog expansion. The hard problem of establishing boundary conditions corresponding to these equations of motion has been successfully tackled. The role of microstructures, in particular the consequences of clustering have been studied in great detail. Among the major challenges posed by granular gases is the fact that they inherently lack scale separation (e.g., mean free times in steady shear flows are comparable to the inverse shear rate), are typically supersonic and break equipartition. This implies that corrections to the Navier-Stokes like hydrodynamic equations should be of importance and indeed it has e.g., been realized that the normal stress differences prevalent in granular gases are a manifestation of such corrections (Burnett). While the traditional experimental and theoretical paradigm for granular gases used to be shear flow it seems that the focus has shifted to vibrated systems, as the latter are easier to handle experimentally. Modern experimental techniques have enabled the measurement of single grain trajectories and full velocity distribution functions (which are often strongly non-Gaussian as systematic kinetic theories predict), convective patterns, shock waves and many other features of granular flows. Perhaps the most interesting finding is that the hydrodynamic theories and their extensions seem to ‘work’ far beyond their nominal range of validity. The dynamics of dense granular gases, the effects of frictional restitution (which are rarely accounted for) and the detailed behavior of granular mixtures are among the numerous exciting and open problems in this field.
Transport Properties in Sheared Granular Flows
Authors: Hsiau Shu-San
Published: May 2008

This paper tends to review the experiments performed in a shear cell device at National Central University. The influences of wall conditions and particle solid fractions were investigated. The glass spheres with a mean diameter of 3 mm were used as granular materials. Three bi-directional stress gages were installed to measure the normal and shear stresses along the upper wall. The image processing technology and particle tracking method were employed to measure the average and fluctuation velocities in the streamwise and the transverse directions. By tracking the movements of particles continually, the variation in the mean-square diffusive displacements with time was plotted and the self-diffusion coefficient was determined. The self-diffusion coefficients in the streamwise direction were much higher than those in the transverse direction. Besides the fundamental observations in a shear device, this paper will briefly describe the technology of “moving granular bed filter” developed at National Central University. This technology is mainly developed for high temperature gas cleanup.
Experimental Studies of Using Water Mist Cooling for the Tempering of Glass
Authors: So¨zbir Nedim , Yao Shi-Chune
Published: May 2008

Very high velocity air jet impingement has been applied during the cooling process of glass tempering. In order to reduce the usage of high-pressure air in the process, it is intended to demonstrate the feasibility of using water mist to enhance the air-cooling. The multiple jet experiments were performed using air jet velocities between 40 and 90 m/sec containing low mass flux of water mist that was varied from 0 up to 0.145 kg/m2sec for each jet. The experiments include different glass thickness. The optimal tempering conditions were explored. The mechanisms of mist cooling are revealed from the experiments of a single water mist jet impinging on hot stainless steel plates. Since the droplets are small, on the order of 20 micron, heat transfer distribution of the water mist has a similar form as the air jet cooling. The total heat transfer coefficient can be viewed as two separable effects: the summation of the heat transfer coefficient of the convective air and of the impinging water flux, respectively. The heat transfer of multiple water mist jets on larger glass is studied. When the liquid flux is too high or when the surface temperature falls below the Leidenfrost temperature, excessive local thermal stress will occur, which leads to cracking of glass. It is possible to reach the optimal tempering with a moderate amount of water applied on the glass surface for a short duration of time. The mist cooling demonstrates a definitive saving on the use of high-pressure air. When using mist cooling, the energy requirements of the system are significantly lowered. The mist cooling creates more refined fracturing in the punching tests of tempered glass. For glass thicker than 3 mm, the particle counts due to water mist improve about 121%. For 2 mm glass, the improvement is about 38%. The mist cooling of the thinnest glass is still not able to give the desired particle counts. But definitive improvement toward this objective is shown. Further studies of other alternatives may give a chance to achieve this goal.
Improvement of Measurement Accuracy of Laser Diffraction Method in Sizing Spray Particles
Authors: Park Nam Su , Kim Yu Dong , Lee Sang Yong
Published: May 2008

Drop size measurement is an important part in studying atomization characteristics and spray behavior. Recently, the laser diffraction method that does not interrupt the spray flow is being widely used. In the present study, a set of reticles (reference particles) with known size distributions, based on the Rosin-Rammler distribution function, were used to evaluate the measurement accuracy of the laser diffraction method. Experimental results showed that Sauter mean diameters (SMD) measured with a laser diffraction particle analyzer were in good agreement with the true values for the entire range of the Rosin-Rammler distribution parameters tested. However, the dispersion parameters in the Rosin-Rammler function were measured to be considerably different from the actual ones, as the particle distribution became monodispersed. Thus, functional expression for the parameter representing the dispersion was proposed in terms of the peak height ratio obtained directly from the light energy distribution information.
Disengagement of a Pendent Liquid Drop From a Vibrating Ceiling
Authors: Kim Ho-Young
Published: May 2008

Small drops adhering to a ceiling under a gravitational field are found in many industrial and natural situations. This work investigates a novel scheme to rapidly remove these pendent drops from a solid surface by vibrating the drop. In the experiments, a water drop pendent from a solid surface is vibrated at a fixed frequency while increasing the vibration amplitude. Upon repeating the experiments using different frequencies, it is revealed that there exist resonant frequencies at which the minimum vibration amplitudes inducing a fall-off of the pendent drops are remarkably less than the detaching amplitudes at neighboring frequencies. These frequencies are supposed to correspond to the resonant frequencies of different drop oscillation modes. They are compared with the resonant frequencies predicted by relatively simple analyses, and the factors causing discrepancy between them are discussed.
Multi-Phase Flow and Condensation in Proton Exchange Membrane Fuel Cells
Authors: Stockie John M.
Published: May 2008

The porous electrodes in a proton exchange membrane fuel cell are characterized by multi-phase flow, involving liquid water and multispecies gases, that are undergoing both condensation and catalyzed reactions. Careful management of liquid water and heat in the fuel cell system is essential for optimizing performance. The primary focus of this study is thus on condensation and water transport, neither of which have yet been studied in as much detail as other aspects of fuel cell dynamics. We develop a two-dimensional model for multi-phase flow in a porous medium that captures the fundamental transport processes going on in the electrodes. The governing equations are discretized using a finite volume approach, and numerical simulations are performed in order to determine the effect of changing operating conditions on fuel cell performance.
3-D Numerical Simulation for Fuel Cell Performance
Authors: Jen Tien-Chien , Chan S. H. , Yan T. Z.
Published: May 2008

A 3-D mathematical model for the PEM fuel cell including gas channel has been developed to simulate fluid flow, current density distribution, and multi-component transport. In order to understand the developing fluid flow and mass transfer process inside the fuel cell channels, the conventional Navier-Stokes equations for gas channel, and volume-averaged Navier-Stokes equations for porous gas diffusers and catalyst layer are adopted individually in this study. A set of conservation equations and species concentration equations are solved numerically in a coupled gas channel and porous media domain using the vorticity-velocity method with power law scheme. Detailed development axial velocity and secondary flow fields at various axial positions in the entrance region are presented. Polarization curves under various operating conditions are demonstrated by solving the equations for electrochemical reactions and the membrane phase potential. Compared with experimental data from published literatures, numerical results of this model agree closely with experimental results. Finally, mass transport equations are solved at a preset condition of electrochemical reaction, and oxygen and hydrogen mole fraction distribution fields are displayed.
Computation of the Conjugating Heat Transfer of Fuel and Oxidant Separated by a Heat-Generating Cell Tube in a Solid Oxide Fuel Cell
Authors: Li Pei-Wen , Schaefer Laura , Wang Qing-Ming , Chyu Minking K.
Published: May 2008

A numerical model is presented in this work to compute the inter-dependent fields of flow, temperature and the concentrations of multiple gases in a single tubular solid oxide fuel cell (SOFC) system. It was supposed that the fuel gas supplied to the fuel cell is from a pre-reformer and thus contains hydrogen and proportions of carbon monoxide, carbon dioxide, steam, and methane. The model takes mixture gas properties of the fuel and oxidant as functions of the numerically obtained local temperature, pressure and species concentrations, which are inter-dependent and intimately related to the electrochemical reaction in the SOFC. In the iterative computation steps, local electrochemical parameters were simultaneously calculated based on the local parameters of pressure, temperature, and concentration of the species available at each step. Upon the convergence of the computation, both local details and the overall performance of the fuel cell could be obtained. The numerical results obtained are helpful for better understanding of the operation of SOFCs.
Influence of Model Inaccuracies on the Prediction of Dynamic System Performance
Authors: Garg Devendra P. , Gulati Navneet
Published: May 2008

A good understanding of system dynamics is imperative to the design of any control strategy. Results of inaccurate models can lead to inefficient controls. However, the formulation of an accurate dynamic model requires high computational power and hence various simplifying assumptions are made while deriving the system equations. In order to illustrate this concept, a simple dynamic experiment of a double-pendulum is formulated and the responses obtained from the derived model and the actual model were compared. Inaccuracies of the derived model clearly showed up in the comparison. By taking into account factors, which were initially omitted for simplifying calculation, the inaccuracies observed could be minimized.
Control of the Rutgers Ankle Rehabilitation Interface
Authors: Yoon Jungwon , Ryu Jeha , Burdea Grigore , Boian Rares
Published: May 2008

This paper presents the control system development of the Rutgers Ankle rehabilitation device. The “Rutgers Ankle” is a haptic interface with a Stewart platform structure driven by six double-acting pneumatic actuators. Each cylinder input is controlled by one set of on/off solenoid valves. For overall system control, an interrupt handler loop is designed based on hardware interrupts. For precise flow rate control of the solenoid valves, a PWM scheme is proposed for a set of two on/off valves. The proposed PWM logic compensates the dead band of the valve response time. A distribution method for the desired pressure differential of the two air chambers of an actuator is proposed. The method is based on the minimization of the difference between the desired and measured pressure. During experiments, one actuator achieved a rise time of 90 ms and 0.3 mm resolution in an independent position control loop. The Rutgers Ankle has a 7 Hz mechanical bandwidth and allows stiffness control for haptic interaction during rehabilitation exercises. The measured performance is believed to be sufficient for ankle rehabilitation purposes.
Experimental and Numerical Investigation of the Flow Behavior in a Tapered Rectangular Sprue
Authors: Derdouri Abdessalem , Ilinca Florin , Kabanemi Kalonji , He´tu Jean-Franc¸ois
Published: May 2008

The present study is part of a continuing effort to obtain a better understanding of the rheological behavior during the injection molding of unfilled and reinforced polymers and help improve the prediction by numerical three dimensional simulation of the process. The slightly tapered rectangular sprue of a centrally gated plaque mold was equipped with flush mounted pressure sensors to monitor the time evolution of the wall shear stress prior to entering the cavity. Two Polycarbonate with different zero-shear rate viscosities were tested at various injection speeds. Atter an initial rise, the wall shear stress in the sprue remains constant during the filling stage of the mold. The transient shear viscosity was determined from the known volumetric rate using a simplified one-dimensional flow approach and compared to the viscosity measured by traditional off-line rheometers. A finite element three-dimensional code is used to simulate the flow in the sprue with small and large width over thickness ratios. The pressures predicted are used in combination with the simplified theory to calculate the viscosity and compare the results from the experiments.
An Intelligent Robotic Walker: Mechanical Design and Control System
Authors: Kececi E. Faruk , Tao Gang
Published: May 2008

This paper presents the mechanical and control system design of a mobile robot designed as a mobility aid for the elderly. Today, with advanced computer control and robotics technologies it is possible to design more intelligent robots, which can help elderly people in their dally life tasks. We have designed an intelligent robotic walker. The main functions of this advanced walker are: following its path with observed control, changing its structural shape to prevent unbalancing the user when walking on a slope, and braking to stop the user falling down. The base of the robot is considered another linkage in the manipulator system, in the adoption of the robot to the slope.A simulation of the system shows the effectiveness of the proposed control method.
Various Robotic Applications of Perturbation/Correlation Method
Authors: Chung Byunghoon , Knuepfer Peter , Lee Sooyong
Published: May 2008

We propose a novel technique for acquiring effective information for obstacle avoidance in mobile robot navigation and for object detection in vision image. Instead of simply receiving data at a single point, we actively give perturbations to the system and measure the response from the system. Correlating the input and the output, we can formulate the correlation function and, useful information such as gradient can be obtained from this function. This algorithm is applied to the obstacle avoidance in mobile robot navigation and the object detection in vision image processing.
Decentralized Kinematic Control of a Cooperating System of Mobile Manipulators
Authors: Abou-Samah Michel , Krovi Venkat
Published: May 2008

In this paper, we examine the development of a decentralized control framework for a modular system of wheeled mobile manipulators that can team up to cooperatively transport a large common object. Each individually autonomous mobile manipulator consists of a differentially-driven wheeled mobile robot (WMR) with a passive, two-degree-of-freedom, planar, revolute-jointed arm mounted in the plane parallel to the base of the WMR. The composite multi-degree-of-freedom vehicle, formed by placing a common object on the end-effector of two (or more) such mobile manipulator systems, possesses the ability to accommodate relative positioning errors of the mobile bases as well as change its relative configuration. Particular attention is paid for the development of kinematic control schemes for mobile manipulators, which take into account the non-holonomic constraints of the base and the presence of passive joints in the manipulator system. The control scheme developed for the individual mobile manipulators is then adapted for the decentralized kinematic control of two mobile manipulators carrying a common object along a desired trajectory. Experimental evaluation of the performance of the resulting approach and the ability of the overall collaborating system to accommodate, detect and correct for relative positioning errors between the mobile platforms is also presented.
Vision Based Path Planning for Mobile Robot Using Extrapolated Artificial Potential Field and Probabilistic Obstacle Avoidance
Authors: Malik Waqar A. , Lee Jae-Yong , Lee Sooyong
Published: May 2008

Mobile robots are increasingly being used to do tasks in unknown environment. The potential of robots to undertake such tasks lies on their ability to intelligently and efficiently locate and interact with objects in their environment. This paper describes a novel method to plan paths for mobile robots in a partially known environment observed by an overhead camera. The environment consists of dynamic obstacles and targets. A new methodology, Extrapolated Artificial Potential Field is proposed for real time robot path planning. The proposed Extrapolated Artificial Potential Field is capable of navigating robots situated among moving obstacles and target. An algorithm for probabilistic collision detection is introduced. The paper summarizes this approach, and discusses the results of path planning experiments using an Amigobot. The result shows that our method is effective.
Hybrid Fault Adaptive Control of a Mobile Robot
Authors: Ji Meng , Zhang Zhen , Biswas Gautam , Sarkar Nilanjan
Published: May 2008

A novel fault adaptive control methodology for a mobile robot is presented in this paper. A bond-graph based modeling technique is used for fault detection and isolation. A hierarchical control accommodation framework is developed for a supervisory controller that determines a suitable control strategy to accommodate the isolated fault. It is shown in the paper that for small degradations, a robust controller achieves fault accommodation without significant loss of performance. However, for large faults, the supervisor needs to switch among several controllers to maintain acceptable performance. Simulation results verify the proposed fault adaptive control technique for a mobile robot.
Consecutive Scanning Scheme: Application to Localization and Dynamic Obstacle Detection for a Mobile Robot
Authors: Lee Jae-Yong , Lee Sooyong
Published: May 2008

This paper presents the mobile robot localization and obstacle detection algorithm using the consecutive range sensor scanning scheme. For known environment, a mobile robot scans the environment using which can rotate 360°. The environment is rebuild using characteristic points which means nodes of two adjacent walls, and obstacle is detected by comparing characteristic points of both original environment and scanned data set. If scanning is done densely for a certain position, inaccuracy of sensor can be overcome to some extent. It is very useful algorithm in detecting the moving obstacle. By comparing two data sets, the movement of an obstacle can be picked out. Furthermore, consecutive scanning data set provides additional localization information so that we can get the robot configuration more precisely.
The Synthesis of Adaptive Control System With Reference Model for Autonomous Underwater Vehicle
Authors: Lebedev Alexander V. , Filaretov Vladimir F.
Published: May 2008

A method of adaptive system synthesis for the control of autonomous underwater vehicle spatial motion is developed. A special nonlinear correcting devices is offered. This devices allows to compensate the complete dynamical coupling and kinematic correlations between this vehicle degrees of mobility at constant control object parameters. An adaptive self-adjustment is used in order to compensate the arbitrary variations of this parameters and external perturbances. The efficiency of synthesised control system is confirmed by numerical simulation.
International Technical Standards: An Overview
Authors: Hebner Robert
Published: May 2008

The growing globalization of industry is stimulating a growing emphasis on international standards. Standards are important because they provide significant economic benefit. They are also costly and much of the benefit is broad-based, i.e. it does not accrue preferentially to those who incur the cost. Finally, there is a highly disaggregated international standards system and at least two very different basic philosophies as to how standard systems should operate. The effect of the individual cost-benefit analysis by organizations may produce a hybrid system that produces both global standards in which each country participates in the development as well as less costly technical and consortium standards.
A New Model for Boundary-Layer Transition Using a Single-Point RANS Approach
Authors: Walters D. Keith , Leylek James H.
Published: May 2008

This paper presents the development and implementation of a new model for bypass and natural transition prediction using Reynolds-Averaged Navier-Stokes (RANS) CFD, based on modification of two-equation, linear eddy-viscosity turbulence models. The new model is developed herein based on considerations of the universal character of transitional boundary layers that have recently been documented in the open literature, and implemented into a popular commercial CFD code (Fluent) in order to assess its performance. Two transitional test cases are presented: (1) a boundary layer developing on a flat heated wall, with free-stream turbulence intensity (Tu∞) ranging from 0.2 to 6%; and (2) flow over a turbine stator vane, with chord Reynolds number 2.3×105, and Tu∞ from 0.6 to 20%. Results are presented in terms of Stanton number, and compared to experimental data for both cases. Results show good agreement with the test cases and suggest that the new approach has potential as a predictive tool.
Large Eddy Simulation of Mixed Convection in a Vertical Turbulent Annular Pipe Flow
Authors: Lee Joon Sang , Xu Xiaofeng , Pletcher R. H.
Published: May 2008

The goal of the present study is to perform a large eddy simulation of vertical turbulent annular pipe flow under conditions in which fluid properties vary significantly, and to investigate the effects of buoyancy on the turbulent structures and transport. Isoflux wall boundary conditions with low and high heating are imposed. The compressible filtered Navier-Stokes equations are solved using a second order accurate finite volume method. Low Mach number preconditioning is used to enable the compressible code to work efficiently at low Mach numbers. A dynamic subgrid-scale stress model accounts for the subgrid-scale turbulence. Comparisons were made with available experimental data. The results showed that the strong heating and buoyant force caused distortions of the flow structure resulting in reduction of turbulent intensities, shear stress, and turbulent heat flux, particularly near the wall.
Tin Solidification in the Presence of Turbulent Natural Convection
Authors: Rocha Luis Joaquim Cardoso , Nieckele Angela O.
Published: May 2008

The solidification process of tin, inside a closed cavity, is numerically investigated by the finite volume method. A non-orthogonal system of coordinates is employed to adapt to the irregular geometry, with a moving mesh to account for the changing domain size. The momentum equations are solved for the contravariant velocity components. The SIMPLEC algorithm handles the coupling between velocity and pressure. A special treatment is given at the liquid-solid interface to obtain the momentum and energy balance. The phase change process is strongly influenced by natural convection in the melt. At the beginning of the process, the cavity is full of liquid, and the natural convection slightly influences the interface shape. But as the liquid region diminishes during the process, the influence of natural convection increases. Further, at the same time as the liquid size region is reduced, the intensity of the flow increases, and the flow can became turbulent, affecting the heat flux at the interface and consequently the size of the solid region. Therefore, the purpose of the paper is to analyze the influence of the turbulent regime on the kinetics of the solidification process. The turbulent flow is taken into account by a low Reynolds number model. The influence of the Rayleigh number on the velocity and temperature field is investigated.