bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Gas-Liquid Two-Phase Flow Patterns in Miniature Channel Having a Gas Permeable Sidewall
Authors: Yang H. , Zhao T. S. , Cheng P.
Published: May 2008

Characteristics of gas-liquid two-phase flow patterns in a miniature square cross-section channel having a gas permeable sidewall have been investigated visually using a high-speed motion analyzer. The problem under consideration is encountered in the design of Direct Feed Methanol Fuel Cells (DMFC). The test section was a horizontally oriented rectangular transparent (Lucite material) channel with its lower wall consisting of a porous plate. Liquid was fed into the test section from its entrance, while gas was injected uniformly into the test section along the lower porous sidewall. The visual study shows the typical flow patterns found in the test section include bubbly flow, plug flow, slug flow, and annular flow. However, unlike the conventional co-current two-phase flow in a channel with gas and liquid uniformly entering from one of its ends, for the flow configuration considered in this work, it was found that two or three of the above mentioned flow patterns appeared simultaneously at different locations of the channel. The length of each flow pattern varied with the flow rates of liquid and gas. A distinct feature of annular flow for the present flow configuration is that small bubbles were continuously generated from the porous plate, which grew by blowing up the liquid film, formed a semi-sphere shape, and then ruptured and released gas into the core flow.
The Development and Validation of a Numerical Model for Non-Homogenous Sheet Heating During Thermoforming Processes
Authors: Rungroungdouyboon Bunyong , Coulter John P.
Published: May 2008

The most common method of heating polymer sheet for thermoforming is radiative heating. In this paper, the radiative heating of opaque thermoplastic sheet has been studied by using a comprehensive numerical modeling approach. The evolution of sheet temperature upon heating, both at the surface and through the thickness was computed assuming one-dimensional transient heat conduction with radiative and conductive boundary conditions. The net-radiation method has been used to compute the total radiative heat on the thermoplastic sheet. Several complex and yet practical sheet heating cases are presented and discussed, and the utility of the newly developed modeling capability is demonstrated.
Assessment of the Driving Capabilities of Persons With Disabilities Using an Advanced Vehicle Interface System
Authors: Zekri S. , Gage A. , Ying S. J. , Sundarrao S. , Dubey R. V.
Published: May 2008

The opportunity for a person with disability to drive a vehicle presents a major step towards a full and independent life. In some cases, employment is not possible due to the inability to control a motor vehicle. Unfortunately, today’s driving evaluations are inadequate because of the qualitative techniques used. This paper presents a new approach to the driving assessment of persons with disabilities in which an advanced vehicle interface system is introduced. This system combines a six-degree-of-freedom force reflecting haptic device and a commercially available vehicle modification system. Innovative ergonomic tasks are presented to determine the appropriate position and orientation of the required driving input device. Further, model based computer assistance is incorporated by using assistance functions such as scaling and tremor filtering. Results, obtained from testing a subject with Muscular Dystrophy (MD), demonstrated that the quantitative ergonomic measurements obtained successfully determined the appropriate position and orientation of the modified steering wheel device.
Application of Learning Control to a Robotic Arm for Exercises
Authors: Ryu Yeong Soon , Ji Zhiming , Yu Qun
Published: May 2008

An application of a simple and effective learning control scheme to a robotic arm for exercise is presented. During exercises, the force applied by a user to an exercise machine varies for different users and for different workouts of the same user. Learning control is used to compensate for the difference between the actual force and the planned force. It is shown through simulation that the learning control method decrease tracking error quickly for both time-invariant and time-varying forcing functions.
Experimental Damage Mechanics of Microelectronic Solder Joints Under Fatigue Loading
Authors: Basaran Cemal , Tang Hong , Nie Shihua
Published: May 2008

Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling is very different. Elastic modulus degradation under thermal cycling, which is considered as a physically detectable quantity of material degradation, was measured by Nano-indenter. It was compared with tendency of inelastic strain accumulation of solder joints in Ball Grid Array (BGA) package under thermal cycling, which was measured by Moire´ interferometry. Fatigue damage evolution in solder joints with traditional load-drop criterion was also investigated by shear-strain hysteresis loops from strain-controlled cyclic shear testing of thin layer solder joints. Load-drop behavior was compared with elastic modulus degradation of solder joints under thermal cycling. Following conventional Coffin-Manson approach, S-N curve was obtained from isothermal fatigue testing with load-drop criterion. Coffin-Manson curves obtained from strain controlled mechanical tests were used to predict fatigue life of solder joints. In this paper it is shown that this approach underestimates the fatigue life by an order of magnitude. Results obtained in this project indicate that thermal fatigue and isothermal mechanical fatigue are completely different damage mechanism for microstructurally evolving materials.
Implementation of a Thermodynamic Framework for Damage Mechanics of Solder Interconnects in Microelectronic Packaging
Authors: Basaran Cemal , Tang Hong
Published: May 2008

A thermo mechanical fatigue life prediction model based on the theory of damage mechanics is presented. The damage evolution, corresponding to the material degradation under cyclic thermo mechanical loading, is quantified thermodynamic framework. The damage, as an internal state variable, is coupled with unified viscoplastic constitutive model to characterize the response of solder alloys. The damage-coupled viscoplastic model with kinematic and isotropic hardening is implemented in ABAQUS finite element package to simulate the cyclic softening behavior of solder joints. Several computational simulations of uniaxial monotonic tensile and cyclic shear tests are conducted to validate the model with experimental results. The behavior of an actual Ball Grid Array (BGA) package under thermal fatigue loading is also simulated and compared with experimental results.
Comparisons and Evaluation of Turbo-Generator and Heat-Engine Driven Space Based Laser Power System Architectures
Authors: Ramalingam Mysore , Donovan Brian , Beam Jerry , Allen Doug
Published: May 2008

Several variations of a notional space based electrical laser power system architecture were evaluated with a general thermal systems analysis. The analysis and evaluations of technology options and feasibility were based on a baseline laser power system concept that incorporated an advanced solar array/battery power combination. Two closed-loop, dynamic cycle system concepts are of interest here, both using H2-O2 to fuel the combustor with the heat engine concept using a PEM fuel cell to regenerate fuel constituents. The first dynamic system is a turbo-generator based concept, and the second is a Brayton cycle based heat engine concept driven by an H2-O2 combustor. Each one of these power generation mechanisms has its own advantages and disadvantages. This first-order thermal analysis aims to compare these various options on a common footing such as system mass, in order to arrive at the most suitable configuration from the various options considered. Several technological enhancements were incorporated in the analysis for the H2-O2 system concepts with special emphasis and advocacy of the use of extremely efficient cryogenic super conducting generators and cryogenic power conditioning equipment as these components can be cooled with the cryogenic effluents before they are combusted. These systems would supply power to a 23.5% efficient electric laser (50% electric to optical power diode pump, and a 47% optical to optical high power laser) with >8 MWrf of output laser power in most cases. This is an extremely high power level, so we predict the systems to be somewhat massive and on the order of 40 metric tons (MT, 1000 kg) or more with high sensitivity to recharge time. For a one-day recharge time, the H2-O2 concept recycling all effluents is twice as massive as the baseline solar system. As the recharge time is extended from one day to more than five, the concept that reclaims the effluents begins to appear more attractive for the turbogenerator-based evaluations. For similar output power, the heat engine based evaluation appears to be more attractive at higher cycle temperatures.
3D Stochastic Modeling of As-Cast Microstructure for Aluminum Alloy Casting
Authors: Xu Q. Y. , Feng W. M. , Liu B. C.
Published: May 2008

A 3D stochastic modeling was carried out to simulate the dendritic grains during solidification process of aluminum alloy, including time-dependent calculations for temperature field, solute redistribution in liquid, curvature of the dendritic tip, and growth anisotropy. The nucleation process was calculated by continuous nucleation. A 3D simplified grain shape model was established to represent the equiaxed dendritic grain. Based on the Cellular Automaton method, a grain growth model was proposed to capture the neighbor cells of the nucleated cell. On growing, each grain continues to capture the nearest neighbor cells to form the final shape. When a neighboring cell has been captured by the other grains, the grain growth along this direction is stopped. Three-dimensional calculations were performed to simulate the evolution of dendritic grain. In order to verify the modeling results, aluminum alloy sample castings were cast in sand and metal mold.
Natural Convection Measurements for a Concentric Spherical Enclosure
Authors: Teertstra Peter M. , Yovanovich M. Michael , Culham J. Richard
Published: May 2008

An experimental test program is described for the measurement of natural convection for an isothermal, heated sphere centrally located in an isothermal, cooled spherical enclosure. A transient test method is used in a reduced pressure environment to provide data for a wide range of Rayleigh number, from the limiting case of laminar boundary layer convection to the diffusive limit. Tests are performed using a fixed outer diameter for four different inner sphere diameters, resulting in diameter ratios in the range 1.5 ≤ do/di ≤ 4.8. The data are in excellent agreement with the exact solution for the conductive limit and are shown to be bounded by a model for the isolated, isothermal sphere.
Investigations on Low Heat Rejection Diesel Engine With Crude Jatropha Oil as an Alternate Fuel
Authors: Murali Krishna M. V. S. , Vara Prasad C. M. , Rajashekar Tandur , Tiwari Supriya , Sujani T.
Published: May 2008

Jatropha oil, a non-edible vegetable oil shows a greater potential for replacing conventional diesel fuel quite effectively, as its properties are compatible to that of diesel fuel. But low volatility and high viscosity of jatropha oil call for hot combustion chamber, which is provided by a low heat rejection diesel engine with threaded air gap piston and liner with superni-90 inserts. The performance of the engine with jatropha oil is obtained with different versions of the engine such as conventional engine and insulated engine at normal and preheat condition of the oil, with varying injection pressure and timing and compared to the engine with pure diesel operation at recommended injection pressure and timing. Increase of thermal efficiency of 18% and reduction of NOx levels by 5% are observed at optimized injection timing and at higher injection pressure with insulated engine at preheat condition of jatropha oil in comparison with pure diesel operation on conventional engine.
The Dispersion in One- and Two-Dimensional Finite Element Solutions to the Heat Equation
Authors: Dauksher W. , Emery A. F.
Published: May 2008

The dispersive errors in the finite element solution to the one- and two-dimensional heat equations are examined as a function of element type and size, capacitance matrix formulation, time stepping scheme and time step size.
A Parametric Study of PEM Fuel Cell Performances
Authors: Wang Lin , Husar Attila , Zhou Tianhong , Liu Hongtan
Published: May 2008

The effects of different parameters on the performances of proton exchange membrane fuel cells were studied experimentally. Experiments with different fuel cell temperatures, humidification temperatures and backpressures of reactant gases have been carried out. Polarization curves from experimental data are presented and the effects of the parameters on the performance of the PEM fuel cell are discussed. The experimental data obtained in this work are used to validate our 3-D mathematical model. It is found that modeling results agree well with our experimental data.
Thermodynamic Analysis of Zero-Atmospheric Emissions Power Plant
Authors: Martinez-Frias Joel , Aceves Salvador M. , Smith J. Ray , Brandt Harry
Published: May 2008

This paper presents a thermodynamic analysis of a natural gas zero-atmospheric emissions power plant with a net electrical output of 400 MW. In this power plant, methane is combusted with oxygen in a gas generator to produce the working fluid for the turbines. The combustion produces a gas mixture composed of steam and carbon dioxide. These gases drive multiple turbines to produce electricity. The turbine discharge gases pass to a condenser where water is captured as liquid and gaseous carbon dioxide is pumped from the system. The carbon dioxide can be economically conditioned for enhanced recovery of oil, or coal-bed methane, or for sequestration in a subterranean formation. The analysis considers a complete power plant layout, including an air separation unit, compressors and intercoolers for oxygen and methane compression, a gas generator, three steam turbines, a reheater, a preheater, a condenser, and a carbon dioxide pumping system to pump the carbon dioxide to the pressure required for sequestration. The computer code is a powerful tool for estimating the efficiency of the plant, given different configurations and technologies. The efficiency of the power plant has been calculated over a wide range of conditions as a function of the two important power plant parameters of turbine inlet temperature and turbine isentropic efficiency. This simulation is based on a 400 MW electric power generating plant that uses turbines that are currently under development by a U.S. turbine manufacturer. The high-pressure turbine would operate at a temperature of 1089 K (1500 °F) with uncooled blades, the intermediate-pressure turbine would operate at 1478 K (2200 °F) with cooled blades and the low-pressure turbine would operate at 998 K (1336 °F). The corresponding turbine isentropic efficiencies for these three turbines were taken as 90, 91 and 93 percent. With these operating conditions, the zero-atmospheric emissions electric power plant has a net thermal efficiency of 46.5%. This net thermal efficiency is based on the lower heating value of methane, and includes the energy necessary for air separation and for carbon dioxide separation and sequestration.
A Precision Plan-to-Action Mapper for Vehicle Control
Authors: Schaefer Frank R. , Haque Imtiaz
Published: May 2008

The vehicle control system described in this paper consists of a discrete controller that computes the control parameters in two major steps: Geometric dynamic planning and plan-to-action mapping. Geometric dynamic planning computes a nominal motion, or ‘gd-plan’ of the vehicle for one control interval. Plan-to-action mapping computes the control parameters so that the gd-plan is performed. This control structure allows the independent modeling of two essential control concepts: motivation and knowledge. Motivation is modeled by computing a desired geometric-dynamic plan. Knowledge is represented through plan-to-action mapping as an approximation of the plant’s inverse system function. This paper describes the development of an extremely precise plan-to-action mapper for use in a vehicle control system that is based on empirical data. This approach is majorm step towards the development of a control structure that is indeed able to adapt to any given plant, or specifically any given vehicle. The paper first describes the development of a suiteable database capturing the vehicle’s input/output behavior. This database can then be used by a curve fitting process to find a formula for the relationship between the vehicle’s; geometric-dynamic behavior and the vehicle’s control inputs. Finally, a number of simulation runs are done to demonstrate the effectiveness of the approach.
Hierarchically Organized Bayesian Networks for Distributed Sensor Networks
Authors: Licht Torsten , Deshmukh Abhijit
Published: May 2008

As sensor hardware becomes more sophisticated, smaller in size and increasingly affordable, use of large scale sensor networks is bound to become a reality in several application domains, such as vehicle condition monitoring, environmental sensing and security assessment. The ability to incorporate communication and decision capabilities in individual or groups of sensors, opens new opportunities for distributed sensor networks to monitor complex engineering systems. In such large scale sensor networks, the ability to integrate observations or inferences made by distributed sensors into a single hypothesis about the state of the system is critical. This paper addresses the sensor integration issue in hierarchically organized sensor networks. We propose a multi-agent architecture for distributed sensor networks. We present a new formalism to represent causal relations and prior beliefs of hierarchies of sensors, called Hierarchically Organized Bayesian Networks (HOBN), which is a semantic extension of Multiply Sectioned Bayesian Networks (MSBN). This formalism allows a sensor to reason about the integrity of a sensed signal or the integrity of neighboring sensors. Furthermore, we can also evaluate the consistency of local observations with respect to the knowledge of the system gathered up to that point.
Threshold Energy Switching and Its Application to Wireless Sensing in High Energy Manufacturing Processes
Authors: Theurer Charles B. , Zhang Li , Kazmer David O. , Gao Robert X.
Published: May 2008

A solid state threshold energy switching device based on a relaxation oscillator is discussed in the context of a self energizing wireless pressure sensor. The study is an integral part of the design of a wireless pressure sensor for in-situ injection molding machine cavity pressure measurement and real time process control. The pressure information is measured using a piezoelectric stack and converted to a train of ultrasonic pulses, using the oscillator based threshold switching device, to a receiver outside of the mold. In this paper the threshold switching device is developed, simulated using a circuit simulation program, and validated experimentally. Its properties are discussed with reference to pressure measurement and acoustic signal transmission.
Transient Model of Heat, Mass, and Charge Transfer as Well as Electrochemistry in the Cathode Catalyst Layer of a PEMFC
Authors: Genevey Daniel B. , von Spakovsky Michael R. , Ellis Michael W. , Nelson Douglas J. , Olsommer Benoiˆt , Topin Fre´de´ric , Siegel Nathan
Published: May 2008

A transient model of the cathode catalyst layer of a proton exchange membrane fuel cell is presented. The catalyst layer structure can be described as a superposition of the polymer membrane, the backing layer, and some additional platinum particles. The model, which incorporates some of the features of the pseudo-homogeneous models currently present in the literature, considers the kinetics of the electrochemical reaction taking place at the platinum surface, the proton transport through the polymer agglomerates, and the oxygen and water transport within the pores as well as the membrane material of the catalyst layer. Due to the lower porosity of this region and the higher liquid water content, the catalyst layer can be current limiting in the fuel cell. Furthermore, since the cost of the catalyst material is critical, it is important to have a model predicting the effective utilization of this catalyst layer as well as one, which gives insights into how it might be improved. Equations are presented for the mass conservation of reactants and products, the electrical and ionic currents, and the conservation of energy. A discussion of a number of the closure relations such as the Butler-Volmer equation employed is included as is a discussion of the initial and boundary conditions applied. The mathematical model is solved using a finite elements approach developed at I.U.S.T.I.
An Investigation of Evaporation, Boiling, and Heat Transport Performance in Pulstating Heat Pipe
Authors: Cai Qingjun , Chen Reh-Lin , Chen Chung-Lung
Published: May 2008

Pulsating heat pipe (PHP) is a latest development in heat pipe technology. In this paper, evaporation and boiling phenomena are investigated, and liquid heat transport performance in a PHP is measured at different fill ratio as well. The observation results show that phase change in the evaporator may occur by two different mechanisms: 1) evaporation and boiling in thin liquid film on the evaporator wall, 2) generation and collapse of tiny bubbles suspended in the liquid slug. Meanwhile, the temperature measurement indicates that temperature gradient between the evaporator and the condenser is related to liquid latent heat, density, viscosity, and mass filled in.
Study of a Minature Thermoacoustic Refrigerator
Authors: Chen Reh-Lin , Chen Chung-Lung , DeNatale Jeff
Published: May 2008

A thermoacoustic refrigerator (TAR) of miniature scale, aimed for low-capacity cooling, was numerically and experimentally investigated. DeltaE (Ward and Swift, 1994) was used to model and optimize the TAR design. MEMS stacks, along with several other materials, were used to produce cooling. The precise control over dimensions and geometry that MEMS technology provides can be critical to cooler performance. A commercial PZT driver was used in this study to deliver acoustic power for heat pumping. The cooler is 1/4λ long in standing-wave configuration and operated at 4 kHz, where the acoustic resonance resides. TAR in other geometry and using in-house drivers were also developed but are not included in this paper (Chen et al., 2002). A pressurized version, aimed for higher power density and efficiency using inert gas mixtures, is under development. The performance, challenges, and a system test bed using LabVIEW are reported.
CHP Self Analysis
Authors: Fischer Steve , Glazer Jason
Published: May 2008

Two techniques are described for preliminary screening of facilities to determine potential cost and energy savings from implementing combined cooling, heating, and power. The first technique can be performed with a simple hand-held calculator and employs average costs for equipment, power, and fuel. The second technique employs a simulation tool run on a desktop computer. It draws upon extensive databases for equipment cost and performance, utility rates, and calculated building electrical and thermal loads.
Utilization of a Graphite Foam Radiator on a Natural Gas Engine-Driven Heat Pump
Authors: Ott R. D. , Zaltash A. , Klett J. W.
Published: May 2008

A natural gas engine-driven heat pump was outfitted with a graphite foam radiator to demonstrate its thermal efficiency and compare it with that of a conventional radiator. A sequence of tests was performed with the graphite foam radiator operating in series with the standard aluminum radiator. Most aluminum air-to-water radiators exhibit an overall heat transfer coefficient up to 100 W/(m2·K). Laboratory experiments have demonstrated that a graphite foam radiator can achieve an overall heat transfer coefficient up to an order of magnitude larger. The mesophase pitch derived graphite foam is a material that offers excellent thermal management capability. The foam has an accessible surface area of 4 m2/g and an open cell structure with graphitic ligaments aligned parallel to the cell walls, giving it an overall bulk thermal conductivity of up to 175 W/(m·K). The bulk thermal conductivity of aluminum is 180 W/(m·K). The density of the graphite foam is a fifth of that of aluminum and its thermal diffusivity is three times greater than aluminum. These properties allow the graphite foam to be utilized in radiator, or any other heat exchanger, designs that are more efficient than conventional radiators. A graphite foam radiator designed to reject a given amount of heat will be smaller in size, weigh less, require less cooling air, and be quicker at removing heat than a conventional aluminum radiator.
Mechanical Adhesion Analysis of Multi-Stepped Double Scarf Joints With Void and Disbond Effects
Authors: Karmarkar Uday , Sancaktar Erol
Published: May 2008

In this paper, some preliminary analysis techniques are presented to help incorporate the effects of the adherend surface topography as a discrete entity in the adhesive joint composite. We believe that topographies obtained on treated surfaces can be approximated by a collection of single and/or multiple scarf, lap, or butt sections, which can be in stepped and/or straight configurations. Consequently, examples of multi-stepped double scarf joints with void, and disbond effects are illustrated to shed more light into the behavior of joints, which are not fully wetted, and contain void and/or disbond sections as a result.
Optimization of Adhesively Bonded Single Lap Joints by Tapering of Adherends
Authors: Nirantar Prasad , Sancaktar Erol
Published: May 2008

The effect of tapering the ends of the adherend on the joint strength and joint deformation behavior of the single lap joint geometry was studied. First, the joints were geometrically modeled using finite element (FE) techniques involving linear, as well as nonlinear (bilinear) material behavior. Then, the FEA results were compared with the experimental results for different configurations of the single lap joints, and the FEA results were found to be consistent with the experimental results with the normal and shear stresses significantly decreasing in the modified geometries over those in unmodified geometries leading to increased loading capacity in modified joints, especially with small-angle taper (~10°).
Stress Analysis of Butt Adhesive Joints of Dissimilar Hollow Cylinders Under Impact Tensile Loadings
Authors: Sawa Toshiyuki , Suzuki Yoshihito , Kido Shoichi
Published: May 2008

The stress variations in butt adhesive joints of dissimilar hollow cylinders under impact tensile loadings are analyzed in elastic and elasto-plastic deformation using a finite element method. The FEM code employed is DYNA3D. The effect of Young’s modulus of the adhesive, adhesive thickness and the inside diameter of the hollow cylinders and Young’s modulus ratio between dissimilar adherends on the stress variations at the interfaces are examined. In addition, a process in rupture at the interface of the joint is analyzed. The stress distributions in the joints under static loadings are also analyzed by an FEM. The characteristics of the stress variations in the joints under impact loadings are compared with those in the joints under the static loadings. Also, the joint strenths under impact loadings are estimated. As the results, it is found that the maximum value of the maximum principal stress σl occurs at the outside of the interface. It is also found that the maximum principal stress σl at the interface decreases as the inside diameter of the hollow cylinders increases. The characteristics of the joints subjected to the impact loadings are found to be opposite to those subjected to the static loadings. In addition, the experiments were carried out to measure the strain response of the butt adhesive joints under impact tensile loads using strain gauges. Furthermore, the joint strengths under impact loadings were measured. Fairly good agreements are observed between the numerical and the measured results.
Rayleigh-Benard Convection During Directional Solidification of a Binary Solution Cooled From the Top
Authors: Kumar P. , Chakraborty S. , Srinivasan K. , Dutta P.
Published: May 2008

In this paper, we investigate the effects of laminar double-diffusive natural convection on directional solidification of binary fluids when cooled and solidified from the top. The study is performed using aqueous ammonium chloride solution as the model fluid. The experiments are performed with an initial concentration of ammonium chloride is less than the eutectic composition, leading to an aiding double-diffusive convection. In this case, solidification leads to the formation of a diffused matrix of dendritic crystals (mushy region) separating the pure solid and liquid regions. Below the two-phase mushy region, Rayleigh-Benard type of cellular convective motions are observed. The cellular motions, which are caused by thermal buoyancy, die once the thickness of the liquid layer falls below a critical value. The features of convective transport are visualised using a sheet of laser light scattered through neutrally buoyant glass particles seeded in the solution. Numerical simulations are also performed, and the agreement with experimental results is found to be good.
Basis Property and Stabilization of a Translating Tensioned Beam Through a Pointwise Control Force
Authors: Guo Bao-Zhu , Xie Yu
Published: May 2008

Introducing a recently developed powerful method, Riesz basis method what is so called, and applying to the stabilization of a translating tensioned beam through a pointwise control force are the two purposes of the paper. An asymptotic analysis, which is different from the one in treating the same problem in literature, is used to get a complete asymptotic expansion of the eigenvalues and eigenfunctions for the beam. The controlled system is written as an evolution equation in a state Hilbert space whose energy norm (induced by inner product) is the total energy of the beam. The spectrum-determined growth condition is obtained by showing that there is a set of generalized eigenfunctions of the system, which forms a Riesz basis for the state space. As a consequence, the stability, particularly the exponential stability of the system is developed. The analysis used here can be extended to other distributed systems and the results significantly improve that in [ASME Journal of Dynamic Systems, Measurement, and Control, 122(2000), 322–331].
Experimental Vibration Control of a Two-Degree of Freedom, State-Switched Absorber System
Authors: Holdhusen Mark H. , Cunefare Kenneth A.
Published: May 2008

A State-Switched Absorber (SSA) is a device capable of instantaneously changing its stiffness, thus it can switch between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers for vibration control. Previous theoretical simulations show that for a system subjected to a multi-harmonic disturbance, using an appropriate logic for switching states, the SSA reduces vibration more effectively than classical tuned vibration absorbers (TVA). This paper considers the experimental performance of the SSA for vibration suppression of an elastically mounted lumped mass base. State switching is achieved using magneto-rheological fluid to connect or disconnect a coil spring in parallel with other coil springs. The stiffness state is controlled by applying or removing a magnetic field across of the MR fluid. Experiments were performed over a range of forcing and tuning frequencies. The SSA system, optimally tuned, outperformed the optimal classical TVA system for all combinations of forcing frequencies.
Micro-Photodeformation Actions of Photostrictive Actuator Patches Applied to Vibration Control of Cylindrical Shells
Authors: Shih Hui-Ru , Tzou H. S.
Published: May 2008

The photostricitve actuator is a new class of distributed actuator that can induce non-contact distributed actuation without utilizing hard-wired connections, due to the photodeformation effect. In this paper, active distributed control of flexible cylindrical shells using discrete photostrictive actuators are investigated and the control effectiveness is evaluated. This paper presents a coupled opto-piezothermoelastic shell theory that incorporates photovoltaic, pyroelectric, piezoelectric and thermal effects, and has the capability to accurately predict the response of a shell to a command illumination applied to the photostrictive actuators. Expressions for the forces and moments that represent the action of the actuator patches have been developed. Governing equations are formulated. Solution procedures based on the modal analysis technique are outlined. The detailed actuator control effectiveness is evaluated with respect to actuator placements. It is shown that by properly positioned the actuators the system performance can be improved. Numerical simulation results also show that the membrane control action is more significant than the bending control action.
Measurement of the Shear Modulus of Tissue-Like Materials Using Magnetic Resonance Elastography
Authors: Hardy Peter A. , Zhang Bao , Gao Dayong , Mitchell Richard J.
Published: May 2008

We developed a technology to measure the shear modulus of tissue-like materials using Magnetic Resonance (MR) imaging. In this technique, called MR elastography or MRE, the sample is vibrated at 100–300 Hz while MR images are made. The shear wave generated by the vibration will propagate into the material at a speed proportional to the square root of the shear modulus. We compared the shear modulus of gel samples measured in this way with the modulus derived from a static compression test and assuming the material is linearly elastic. The results show good agreement of the two methods provided the shear modulus of the material is below approximately 10 kPa. Differences in the two measurements are explainable by differences in the compression rate of the two techniques.
Growth Kinetics and Thermal Stress in AlN Bulk Crystal Growth
Authors: Wu Bei , Ma Ronghui , Zhang Hui , Dudley Michael , Schlesser Raoul , Sitar Zlatko
Published: May 2008

Group III nitrides, such as GaN, AlN and InGaN, have attracted a lot of attention due to the development of blue-green and ultraviolet light emitting diodes (LEDs) and lasers. In this paper, an integrated model has developed based on the conservation of momentum, mass, chemical species and energy together with necessary boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The simulation results have been compared with temperature measurements for different power levels and flow rates in a reactor specially designed for nitride crystal growth at NCSU. It is evident that the heat power level affects the entire temperature distribution greatly while the flow rate has minor effect on the temperature distribution. The results also show that the overall thermal stress level is higher than the critical resolved shear stress, which means thermal elastic stress can be a major source of dislocation density in the as-grown crystal. The stress level is strongly dependent on the temperature gradient in the as-grown crystal. Results are correlated well with defects showing in an X-ray topograph for the AlN wafer.
Numerical Simulation of Flow and Heat Transfer Inside a Micro-Channel With One Dimpled Surface
Authors: Wei X. J. , Joshi Y. K. , Ligrani P. M.
Published: May 2008

Steady, laminar flow and heat transfer, inside a rectangular microchannel with a dimpled bottom surface, are numerically studied using FLUENT 5.5. The microchannel is 50 μm deep and 200 μm wide. The dimples are placed in a single row of along the bottom wall with a pitch of 150 μm. The dimple depth is 20 μm, and the dimple print diameter is 98 μm. Fully developed periodic velocity and temperature boundary conditions are used at the inlet and outlet of one unit cell of the dimpled micro-channel. The numerically predicted, laminar, micro-scale flow characteristics are compared to results from macro-scale studies with turbulent flow. Some of the secondary flows into and out of the dimple, and the recirculating flow within the dimple are similar for both situations. However, the type and number of vortex structures shed from the dimples are significantly different for the laminar-micro-scale flow and turbulent-macro-scale flow. Heat transfer enhancements are present for both situations, but they are somewhat smaller in the laminar-micro-scale flow. In the latter case, these augmentations (relative to a channel with smooth walls) are present both on the bottom-dimpled surface, and on the sidewalls of the channel, and are mostly due to shear layer reattachment, secondary flows produced near the edges of the dimples, and thermal boundary layer thinning. The pressure drop penalties in the laminar-micro-scale flow are either equivalent to, or less than values produced in smooth channels with no dimples.
Graphite Foam Thermosyphon Evaporator Performance: Parametric Investigation of the Effects of Working Fluid, Liquid Level, and Chamber Pressure
Authors: Coursey Johnathan S. , Roh Hongkoo , Kim Jungho , Boudreaux Paul J.
Published: May 2008

Graphite foams have recently been developed at ORNL and are beginning to be applied to thermal management of electronics. These foams consist of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a thermal diffusivity about four times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. The use of graphite foam as the evaporator of a thermosyphon is investigated due to its potential to transfer large amounts of energy without the need for external pumping. A preliminary optimization of the parameters governing evaporator performance is performed using 2-level factorial design. Performance of the system with both PF-5060 and PF-5050 were examined as well as the effects of liquid level and chamber pressure.
The Learning Cobot
Authors: Boy E. S. , Burdet E. , Teo C. L. , Colgate J. E.
Published: May 2008

Cobots (COllaborative roBOTS) are passive devices that assist humans by guiding motion along software-defined paths. This paper introduces intuitive and efficient tools to design such paths. The operator creates a guiding path by walk-through path programming, tracing a path in free mode. A B-spline fit to this path becomes the guideway. The operator can locally define and modify the B-spline guiding path by moving the control points on a dedicated graphical user interface using a computer mouse. During movement, the operator avoids obstacles and handles sensing errors by using the elastic path planner to deviate from the guiding path. Collaborative learning lets the operator optimize a guiding path in a few tries to adapt it to the specific task and environment. These tools have been implemented and extensively tested on the Scooter cobot.
Resolution Limits of Nanoscale Thermal Processing With the Atomic Force Microscope
Authors: King William P. , Goodson Kenneth E.
Published: May 2008

A heated atomic force microscope cantilever can raise the temperature of a substrate at the tip-substrate contact to over 500 °C while not substantially raising the temperature of the nearby substrate not in contact with the tip. Models based on continuum solid contact and sub-continuum heat conduction in the tip and in the sample predict that the hot spot could be as small as 2 nm in diameter. This approach to nanoscale thermal processing could be used for fundamental studies of temperature-dependant reactions using small numbers of molecules or atomic clusters, or applications in thermomechanical manufacturing. The resolution limits of nanoscale thermal processing in time, space, and temperature, depend upon the cantilever design, the tip-sample contact, and the substrate material. This paper explores solid contact and thermal conduction between a heated silicon cantilever tip and three different substrates: silicon, a thick metal film, and a thick amorphous layer.
Finite Element Study of Double Diffusive Convection and Solidification Under the Combined Influence of Microgravity and Magnetic Fields
Authors: Li K. , Li B. Q. , de Groh H. C.
Published: May 2008

A finite element model is presented for the g-jitter induced double diffusive convection and solidification phenomena with and without the presence of magnetic fields in a Sn-doped Bi single crystal growth system planned for space experiments in space vehicles and the International Space Station. The model is developed based on the deforming finite element formulation with the penalty formulation for pressure approximation and an isothermal front tracking algorithm is used to predict the solid-liquid interface. Extensive numerical simulations are carried out and studied parameters include the effects of solutal striation on the solidification front location and interface morphology under both steady state and g-jitter (or time varying gravity perturbations) conditions with and without the presence of a magnetic field. Both synthesized g-jitter and real g-jitter taken from space flights are used, with the former intended to provide a fundamental understanding of system performance and later to obtain quantitative information in real flight environments. Computed results show that the concentration effects on interface morphology must be considered for an accurate prediction of solidification interface morphology. Also, an applied magnetic field can be very useful means to suppress the deleterious g-jitter induced convection and solutal striation and their effects on solidification.
Solving Radiative Transfer Equation in Scattering Plane-Parallel Medium Using Wavelets Approximation
Authors: Guven Oguzhan , Wang Bryan Y. , Bayazitoglu Yildiz
Published: May 2008

Wavelet analysis is presented for solving the radiative transfer equation for a scattering medium in a one-dimensional plane-parallel geometry. Some properties of the wavelet transform for numerical approximation of radiative heat transfer are demonstrated. The governing equations are reduced to a system of first-order ordinary differential equations. Linear anisotropic scattering is assumed in order to compare the results with the previous researchers. The method of analysis is quite general since it only requires that the scattering phase function is square integrable. The numerical solutions indicate that wavelet approximation is promising.
Experimental and Numerical Studies of Short Pulse Propagation in Model Systems
Authors: Kumar Sunil , Guo Zhixiong , Aber Janice , Garetz Bruce
Published: May 2008

In this paper experimental and numerical studies of the propagation of short-pulsed lasers through scattering and absorbing media are presented. Experimental results of a 60 ps pulse laser transmission in tissue phantoms are obtained and compared with Monte Carlo simulations. Good agreement between the Monte Carlo simulation and experimental measurement is found. Three models are developed for the simulation of short pulse transport. Benchmark comparisons among the Monte Carlo (MC), transient discrete ordinates method (TDOM) and transient radiation element method (TREM) are conducted.
Turbulence-Radiation Interactions in Flames: A Chaotic-Map Based Formulation
Authors: Xu Ying , McDonough J. M. , Mengu¨c¸ M. Pinar
Published: May 2008

In this paper we report initial efforts in developing large-eddy simulation (LES) subgrid-scale (SGS) models capable of treating turbulence-radiation interactions in sufficient detail to permit calculation of radiation intensity fluctuations on small scales. These models are constructed with a fluctuating component consisting of a discrete dynamical system (chaotic map) and are thus completely deterministic. We present an outline of the development of this formulation and then employ experimental data to generate large-scale behavior permitting what might be viewed as part of an a priori test of the SGS model. We display spatially extensive instantaneous fluctuating temperatures produced by the model as well as time series of fluctuating intensity calculated from the radiative transfer equation at several heights in a pool fire. We conclude that such results are physically realistic (and very efficiently computed) and warrant continued investigations, but we have at this time not yet completely validated the approach due to lack of detailed laboratory data.
Heat Transfer Correlations for a CVD Optical Fiber Coating Process
Authors: Iwanik Patricia O. , Chiu Wilson K. S.
Published: May 2008

A numerical heat transfer study of the chemical vapor deposition coating process used in the manufacture of optical fibers is conducted. A finite volume model, developed to study gas flow and heat transfer in the reactor and heat transfer within the fiber itself, is used. A parametric correlation relating percent temperature drop to the Peclet number and dimensionless fiber radius is determined. This correlation is expanded upon to obtain a correlation for the amount of energy loss as the fiber travels through the reactor. These equations are valid for fiber radius values ranging from 62.5 to 200 μm, and for draw rates ranging from 0.25 to 2.0 m/s.
Finite Element Analysis of TV Panel Glass During Cooling
Authors: Druma Calin , Druma Adriana M. , Alam Khairul M. , Hoque Azizul
Published: May 2008

A finite element software has been used to determine the temperature history in forming a TV glass panel during hot pressing in a metal mold, and the controlled cooling cycle. The temperature history is then used to calculate the stress and strain history in the glass panel. The goal of the simulation model is to predict the resulting stress and strains due to forming and cooling process that takes place during the manufacturing of the TV panel. DEFORM 3D software has been used to carry out the numerical simulation.