bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Hypothermia on the Oxygen Delivery to Cerebral Tissue: Analysis Using a Compartmental Model
Authors: Ley Obdulia , Bayazitoglu Yildiz
Published: April 2008

This paper studies the effect of temperature in the cerebral oxygen absorption and delivery using a compartmental model of oxygen transport which introduces the temperature dependence of factors such as the cerebral blood flow, the oxygen dissociation curve, and the tissue metabolic activity. The variations of the oxygen delivered to the tissue for the case of normoxia and hypoxia are studied, as well as the tissue oxygen delivery during different cooling strategies. The goal of the present study is to understand the effects of temperature in the oxygen uptake, and to determine a safe temperature limits for hypothermic treatment maximizing tissue oxygen delivery. From the calculations it is seen that the oxygen content falls in the vascular and tissue compartments during hypothermia and that this effect is aggravated by hypoxia.
Dynamic Self-Assembly in Confined Micro-Domains
Authors: Liu Dong , Maxey Martin , Karniadakis George
Published: April 2008

We simulate dynamic self-assembly of paramagnetic beads in domains of rectangular, triangular and circular cross-section. We demonstrate that depending on the magnetic field, the number of microparticles, and the shape of microdomain, different self-assembled structures can be produced. This provides an exciting possibility for making reconfigurable multi-functional microdevices, and may also suggest new protocols for fabricating three-dimensional microsystems and nanosystems.
Experimental Measurement of Glass to Mold Heat Transfer for Computational Modeling of Container Production
Authors: Hyre Matthew R. , Underwood Brenton L.
Published: April 2008

Recent advances in numerical simulation capabilities have made the modeling of glass container forming processes feasible. These forming models must include large free surface deformations, viscoelastic behavior, conjugate heat transfer, and complex contact phenomena between the glass and the forming molds. One of the most critical inputs to these models is the heat flux between the glass and mold. A simple one-dimensional heat transfer model was developed for use in conjunction with a complex three-dimensional forming model to determine the heat flow between the glass and forming mold. Initial comparisons to experimental results indicate the simple model captures the primary physics of heat flow during forming. This paper describes an experimental effort to determine the time varying contact conductance between molten glass and container forming molds. The experimental apparatus is capable of independently varying the glass pressure, glass temperature, mold temperature, and glass type. Initial validation of the experimentally determined contact conductance function in conjunction with the one-dimensional heat transfer model utilized within a glass forming model indicate good agreement between calculated and measured results. These forming models are now able to determine final glass container properties without having to resort to the trial-and-error process currently utilized in glass container production.
Shape Control of Tensegrity Plates: An Experimental Study
Authors: Chan Wai Leung , Solari Soren , Skelton Robert E.
Published: April 2008

Tensegrity is a special class of tension-trusses. Strings play an important role in the deployment and shape changing of these structures. A simple class-1 tensegrity unit consists of 3 bars and 9 strings. This unit can be arranged to form a tower or a flat plate. With the integration of sensors and actuators, the tower and plate can be a smart structure. In this paper, we demonstrate the shape changing of a 7-unit tensegrity structure from a flat plate to a parabolic dish by controlling the length of strings in each unit. This provides a feasible structure for a next generation shape changing antenna and space telescope.
Comparison of Head Impact Data for Occupant Computer Predictions and Sled-Buck Crash Tests of Front Adult to Rear Child Interaction in Rear Impact
Authors: Saczalski Kenneth J. , Sances Anthony , Kumaresan Srirangam , Pozzi Mark , Saczalski Todd K.
Published: April 2008

In this study, computer simulations of rear impacts were performed with an available ATB (Articulated Total Body) computer code to demonstrate an efficient and accurate means for assessing safety performance and hazards associated with occupied front seat collapse into a rear seat area occupied by children. The analysis considered a wide range of different sized front-seated adults (i.e. 50 kg females to 110 kg males), various types of front seats with a range of ultimate collapse strengths (i.e. 3.5kN up to 12.5kN), and various impact severities with speed changes between 20 to 50 kph. A 3 year-old child was used as the model for the rear child surrogate seated in the backbench seat of a 2-door sedan. An actual vehicle crash pulse was used as the basis for the analysis pulses. After performing the computer analysis predictions, sled-buck experimental tests were run with the same parameter range, and a full vehicle interior, to validate the human model predictions. Predicted head accelerations for the rear seated child and the front-seated adult were compared with the test results. Good correlation was achieved for the predicted and test head accelerations, as well as the resultant “head injury criteria” curves with actual accident cases of injured children.
Electron Spin Resonance Investigations on Polystyrene-Carbon Nanotubes Composites
Authors: Chipara Mircea , Sankar Jagannathan , Hui David
Published: April 2008

Electron spin resonance investigations on nanocomposites obtained by dispersing carbon nanotubes within polystyrene are reported. The temperature dependence of ESR lines in the range 290 K to 420 K is investigated. It is for the first time that the effect of the polymeric matrix on the electron spin resonance spectra of carbon nanotubes is reported.
A Study of Control Methods for the Braking System on Passenger Multiple Units
Authors: Nankyo Masanobu
Published: April 2008

As well known, the mechanical (friction, pneumatic) brake system on trains contains some non-linear elements. So it has been difficult to control the speed or acceleration of trains according to desired patterns. This paper reviews our research on the control method of the physical performance of train running such as acceleration (deceleration) by mechanical braking devices. One of our approaches is the introduction of the feedback control into the brake control system. Mathematical models of non-linear elements in the brake system and some effective methods of controller design are proposed with both simulation and experimental results. Another approach is the real time estimation of the friction forces between a brake shoe and a wheel tread. Friction has severe non-linearity; however it can not be measured easily on running trains. We propose the introduction of the onboard real-time estimation method of friction coefficients using the speed information which can be obtained easily in the existing brake system.
Feasibility Study of Absorption Chillers With a Low Temperature Heat Source
Authors: Martin Viktoria , Setterwall Fredrik
Published: April 2008

Low temperature energy powering an absorption chiller will make more energy sources available for comfort cooling as compared to conventional heat driven chillers. Solar energy, industrial waste heat and heat from combined power and heat generation are examples of sources for driving energy. Also, the distribution of energy for comfort cooling could be made efficiently by transportation of hot water to the chiller situated near to the customers. Absorption chillers driven by temperatures lower than 90°C (194°F) are in general not available as an “off-the-shelf product.” Usually the low temperature driven chillers are custom made to fit to the local conditions with respect to temperatures of the driving energy and of the cooling water. The optimal design of a chiller is dependant on the temperature of the driving energy as well as on the temperature of the available heat sink for cooling the absorber and the condenser. A scheme for optimization of the chiller with respect to the size of the heat transfer surfaces and of the temperature drop of the driving energy and of the cooling water is presented herein. Presented results illustrate the dramatic effect on the size of the absorber by changing the cooling water temperature, and the equally dramatic effect on the size of the condenser and generator by changing the temperature of the driving energy. Clearly, lowering the heat source temperature and/or increasing the heat sink temperature increases the capital cost for a chiller. However, when coupled to combined heat and power generation, reasonable pay-back times have here been demonstrated for low temperature driven absorption chillers due to the increased electricity production in the overall system.
Prediction of NCAP Star Rating Probability Distribution of a Passenger Vehicle
Authors: Deng Bing , Beltramo Mark A. , Wang J. T.
Published: April 2008

This paper presents a statistical method to predict NCAP (New Car Assessment Program) star ratings at early stages of the vehicle development process when only limited vehicle information, such as weight and a few basic dimensions, is available. The heart of this method is a probabilistic model, in which the probability distribution of NCAP star ratings, conditional on vehicle characteristics, is estimated using residual analysis. Seventy-nine NCAP tests from model year 1999 to model year 2002 were collected from NHTSA public database and used for the analysis. Given a vehicle’s weight and basic dimensions, the estimated probabilities reflect variations among similar existing vehicles due to detailed vehicle structure design, interior geometry layout, restraint system design, and the inherent variability of hardware and crash testing. The statistical method developed in this study provides a fast, probabilistic assessment of a concept vehicle’s potential NCAP performance.
Vibration Control in a Flexible Beam Using a Conservative Force
Authors: Nudehi Shahin S. , Mukherjee Ranjan , Shaw Steven W.
Published: April 2008

The use of end forces for vibration control in structural elements is considered in this paper. The control process involves direct vibration measurement and observer-based estimation of vibration modal amplitudes, which are used to determine when to apply (or increase) an end load such that it will remove vibration energy from the structure. For this study we consider the transverse vibrations of a cantilever beam with a buckling type of end load that can be switched between two values, both of which are below the buckling threshold. The stability of the control system is proven using a Lyapunov analysis, and its effectiveness is demonstrated using simulations and physical experiments. It is shown that the effectiveness of the approach is affected by the bandwidth of the actuator and the attendant characteristics of the filter, the level of the control force, and the level of the end force when it is not actuated. The experiments employ a beam fitted with a cable mechanism and motor for applying the end force, and a piezoelectric patch for taking vibration measurements. It is shown that the first two beam modes, that is, those within the bandwidth limitation of the motor, are very effectively controlled by the proposed scheme.
Modeling the Wall Pressure Spectrum in Turbulent Pipe Flows
Authors: Lysak Peter D.
Published: April 2008

An important source of vibration and noise in piping systems is the fluctuating wall pressure produced by the turbulent boundary layer. One approach to calculating the wall pressure fluctuations is to use a stochastic model based on the Poisson pressure equation. If the model is developed in the wavenumber domain, the solution to the wavenumber-frequency spectrum can be expressed as an integral of the turbulent sources over the boundary layer thickness. Models based on this formulation have been reported in the literature which show good agreement with measured pressure spectra, but they have relied on adjustable “tuning” constants to account for the unknown properties of the turbulent velocity fluctuations. A variation on this approach is presented in this paper, in which only well-known “universal” constants are used to model the turbulent velocity spectrum. The resulting pressure spectrum predictions are shown to be in good agreement with canonical data sets over a wide range of Reynolds numbers.
Determination of Strength and Damping Characteristics of Carbon Nanotube-Epoxy Composites
Authors: Rajoria Himanshu , Jalili Nader
Published: April 2008

In this paper, the strength and damping properties of carbon nanotube-epoxy composites are examined. Carbon nanotubes (Single-walled and Multi-walled) were grown on stainless steel substrates using thermal chemical vapor deposition process. The nanotube-epoxy composites were then prepared by applying a layer of epoxy on the grown nanotubes and a PZT actuator was attached on this layer. The composite beam consisting of steel, nanotube-epoxy layer and PZT actuator was used as a cantilever beam for vibration experiments in order to determine the enhancement in strength and damping properties of the nanotube-epoxy layer. Several different samples were prepared for this purpose. Impulse and frequency sweep tests were conducted on these beams to obtain the impulse response and frequency response functions. Fast Fourier Transform of the impulse response was used to find the natural frequency of the composite beam. It was observed that there was an increase in the stiffness by using multi-walled nanotubes in the epoxy, while the damping ratio increased by using single-walled nanotubes. The stick-slip mechanism is discussed in order to explain the results obtained.
An Erosion Index for Wire Electrode Materials in EDM
Authors: Schacht Benny , Verheyen Raf , Kruth Jean-Pierre , Lauwers Bert
Published: April 2008

In this paper, the authors propose an erosion index for wire materials or wire coatings. In sinking EDM research and practice, an erosion index is commonly available. In wire EDM few efforts have been made to identify possible electrode materials from the point of view of cutting speed. The index is based on physical understanding of the process and uses thermal properties of the electrode material, as is the case for the sinking EDM erosion index. The most important materials used as a coating for wire electrodes, like Zn, Cu, W and Mo, are analyzed and the proposed index is in good correlation with experimental cutting data, both from literature reports and own experiments. The theory can also be applied to alloys, such as brass (Cu-Zn) with different amounts of zinc.
A Numerical Study on the Successive Impingement of Droplets Onto a Substrate
Authors: Tong Albert Y. , Kasliwal Saurabh , Fujimoto Hitoshi , Takuda Hirohiko
Published: April 2008

Numerical simulations of successive impingement of water droplets onto a substrate have been performed. The objective is to understand the hydrodynamics of the impingement process, particularly the interaction between successive droplets. The Navier-Stokes equations are solved using a finite-volume formulation. A two-step projection method is used along with a fixed non-uniform staggered rectangular grid. The free surface of the liquid is tracked by the volume-of-fluid method with a second order accurate piecewise-linear scheme. A continuum surface force model is used to calculate the surface tension force. A dynamic contact angle model which plays an important role in the deformation process is implemented. The method provides a comprehensive model of the hydrodynamic aspect of the impingement process. The effects of several key parameters on the hydrodynamics of the collision have been studied. These include: dynamic and static contact angles, droplet impact velocity, and inter-droplet spacing. The spreading and recoiling of droplets as well as the internal flow field are examined. The numerical results are compared with experimental data and are in general agreement within the confines of the experiment.
Interaction Phenomena of Two Water Droplets Successively Impacting Onto a Solid Surface
Authors: Fujimoto Hitoshi , Shiotani Yu , Tong Albert Y. , Takuda Hirohiko
Published: April 2008

This study is concerned with the deformation behaviors of two droplets impinging successively onto a solid. Photographic means is used to understand the physics of the interaction phenomena between the two droplets. Water droplets of diameters between 0.39 mm and 0.65 mm with impact velocities ranging from 2.0 to 5.0 m/s are examined. The temperature of the solid surface is set at 25, 300 and 500 °C. The effects of varying solid surface temperatures, impact velocities of droplets and time intervals between the successive discharges on the collision behavior of the two impinging droplets are studied.
Axisymmetric Solutocapillary Convection in Microencapsulation
Authors: Subramanian Pravin K. , Zebib Abdelfattah , McQuillan Barry
Published: April 2008

Hollow spherical shells used as laser targets in inertial confinement fusion (ICF) experiments are made by microencapsulation. In one phase of manufacturing, the spherical shells contain a solvent (fluorobenzene, FB) and a solute (polystyrene, PAMS) in a water-FB environment. As the solvent evaporates it leaves behind the desired hardened plastic spherical shells, 1–2 mm in diameter. Perfect sphericity is demanded for efficient fusion ignition. Marangoni instabilities driven by surface tension dependence on the FB concentration could be the source of the observed surface roughness (buoyant forces are negligible in this micro-scale problem). Here we model this drying process, investigate conditions for incipient instabilities, and compute nonlinear axisymmetric convection.
Transient Thermal Management of Microelectronics Using Free Liquid Jet Impingement
Authors: Bula Antonio J. , Rahman Muhammad M.
Published: April 2008

The results of numerical simulation of a transient heat transfer process when a free jet of high Prandtl number fluid impinges perpendicularly on a solid substrate of finite thickness containing discrete electronics on the opposite surface are presented. The numerical model was developed considering both solid and fluid regions and solved as a conjugate problem. Equations for the conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries as well as at the solid-liquid and liquid-gas interfaces. In the solid region, only heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. The number of elements in the fluid and solid regions were determined from a systematic grid-independence study. A non-uniform grid distribution was used to adequately capture large variations near the solid-fluid interface. Computed results included the local and average heat transfer coefficients at the solid-fluid interface. Computations were carried out to investigate the influence of different operating parameters such as jet velocity and plate material. It was found that the average heat transfer coefficient is maximum at early stages of the transient process and decreases gradually with time to the final steady state condition.
Stability Analysis of a Linearized MEMS
Authors: Khazaei A. , Rastgaar Aagaah M. , Mahinfalah M. , Mahmoudian N. , Nakhaie Jazar G.
Published: April 2008

This paper presents the stability theory and dynamic behavior of a micro-mechanical parametric-effect resonator. The device is a MEMS time-varying capacitor. The nonlinear dynamics of the MEMS are investigated analytically, and numerically. Applying perturbation methods, and deriving an analytical equation to describe the frequency response of the system enables the designer to study the effect of changes in the system parameters that can be used for design and optimization of the system.
Dislocation Nucleation at Heterogeneities of Crystal Surfaces
Authors: Li Chengzhi , Xu Guanshui
Published: April 2008

Dislocation nucleation at surface heterogeneities such as steps is analyzed based on the Peierls-Nabarro dislocation model. By modeling a surface step as part of a three-dimensional crack surface, the half space problem is transferred into an equivalent three dimensional crack problem in an infinite medium. The profiles of embryonic dislocations, corresponding to the relative displacements between the two adjacent atomic layers along the slip planes, are then rigorously solved through the variational boundary integral method. The critical conditions for dislocation nucleation are determined by solving the stress dependent activation energies required to activate embryonic dislocations from their stable to unstable saddle point configurations. The effects of step geometry are analyzed in detail. The results show that the atomic scale steps can significantly facilitates dislocation nucleation from stressed crystal surfaces. While the presented methodology of incorporating atomic information into continuum approach is noteworthy for providing insights of energetics of the atomic process involved in dislocation nucleation, further direct atomic simulation appears to be in need to correlate the effectiveness of this approach.
Noisy Impact Oscillators
Authors: Park Jun H. , Sri Namachchivaya N.
Published: April 2008

The purpose of this work is to develop an averaging approach to study the dynamics of a vibro-impact system excited by random perturbations. As a prototype, we consider a noisy single-degree-of-freedom equation with both positive and negative stiffness and achieve a model reduction; i.e., the development of rigorous methods to replace in some asymptotic regime, a complicated system by a simpler one. To this end, we study the equations as a random perturbation of a two-dimensional weakly dissipative Hamiltonian system with either center type or saddle type fixed points. We achieve the model-reduction through stochastic averaging. Examination of the reduced Markov process on a graph yields mean exit times, probability density functions, and stochastic bifurcations.
Imaging of Port Wine Stain Lesions Using a Multi-Sensor Photoacoustic Probe
Authors: Viator John S. , Jacques Steven L. , Aguilar Guillermo
Published: April 2008

Successful treatment of port wine stain (PWS) birthmarks in human skin utilizes cryogen spray cooling (CSC) in conjunction with laser treatment. CSC pre-cools the epidermis to protect it from subsequent laser irradiation which raises the temperature of both the epidermis and the deeper PWS. As the epidermal temperature is depressed by cryogen, damage to the skin surface is minimized while the PWS reaches temperatures sufficient to permanently damage the lesion. In order to optimize cooling and laser heating dosages and to properly guide laser therapy, the spatial relationship of epidermal melanin and PWS must be known. Photoacoustic depth profiling of human skin uses low energy, nanosecond pulses of laser light to induce acoustic waves in optically absorbing media, such as blood and melanin. We used a 532 nm Nd:YAG laser to measure total epidermal melanin content in human skin, comparing the results with visible reflectance spectroscopy. Furthermore, we performed numerical simulations of photoacoustic generation in skin, showing that a hemisperical acoustic sensor array could be used to reconstruct the rete pattern of epidermal melanin in the basal layer. Finally, we built a hemispherical probe for use in future experiments for imaging of human skin.
Continuous Low Power Pre-Concentrations for Distributed Microscale Trace Gas Analysis
Authors: Muntz E. P. , Young M. , Han Y. L.
Published: April 2008

Continuously operating pre-concentrators for mobile and distributed trace gas analyzers have been investigated. Micro/meso-scale trace gas concentrations increasing by a factor of 10 per stage appear to be realistic. At sampling flow rates of a few tenths of a mL/s the pumping power costs can be as low as 50 mW. Separation membranes based on quantum filtering, size filtering and diffusive mass filtering are compared. Dual function size and diffusive mass filtering membranes are the most attractive possibility. Candidate pumping systems are discussed. Concentration cascades are possible and an illustrative three stage cascade is discussed.
Numerical Study of Fuel Flow Through Small Orifices
Authors: Arias Diego A. , Mueller Stephanie I. , Shedd Timothy A.
Published: April 2008

Fuel delivery in carburetors strongly depends on the flow characteristics through a small orifice whose function is to limit the flow between a constant pressure reservoir and a fuel tube. The geometry of this orifice is developed by a trial and error procedure, often without a good understanding of the underlying physics of the flow. In this work, a commercial CFD package was used to perform a numerical simulation of the flow through square edged orifices in order to study the effect of individual parameters on the discharge coefficient, the development of the boundary layer and the velocity profile at the exit of the orifice. Parameters of the study included orifice diameter, length and fuel properties. The simulation used a two-dimensional, axisymmetric, fully turbulent two-equation model in single-phase flow, and was validated by comparison with experimental discharge coefficients of orifices.
Bucket3D: An Innovative Design System for Analysis and Manufacturing of Steam Turbine Buckets
Authors: Hou Ko-Hsiu , Xiong Yuexi , He Bert , Murphy John
Published: April 2008

An innovative design system for analysis and manufacturing of steam turbine buckets has been developed in this work in order to improve design quality and increase productivity. Several enabling technologies have been deployed in the development of the new design system such as Intelligent Master Modeling (IMM), automated mesh generation, and Linked Model Environment (LME) for analysis and manufacturing. The novel features in the system include a modeling framework that helps standardize bucket geometry construction, an automation scheme that minimizes reliance on custom coding, a set of generic and easy to use graphical user interfaces, and parametric airfoil sections for manufacturing inspection. The system has been extensively validated and is being used for production applications.
Investigation of Wire Electrical Discharge Machining of Thin Cross-Sections and Compliant Mechanisms
Authors: Miller Scott F. , Shi Enhui , Kao Chen-C. , Shih Albert J. , Qu Jun
Published: April 2008

The wire electrical discharge machining (EDM) of cross-section with minimum thickness and compliant mechanisms are studied. Effects of EDM process parameters, particularly the spark cycle time and spark on-time on thin cross-section cutting of Nd-Fe-B magnetic material, carbon bipolar plate, and titanium are investigated. An envelope of feasible wire EDM process parameters is generated for Ti. The application of such envelope to select suitable EDM process parameters for micro feature generation is demonstrated. Scanning Electron Microscopy (SEM) analysis of EDM surface, subsurface, and debris are presented. SEM observations lead to a hypothesis based on the thermal and electrostatic stress induced fracture to explain the limiting factor for wire EDM cutting of thin-sections. Applications of the thin cross-section cutting for EDM compliant mechanisms are discussed.
Infinite Beams as Models of Track Transient Vibrations
Authors: Sowinski Bogdan , Drozdziel Jozef
Published: April 2008

In the paper, an attempt to build solution of transient vibrations of railway track is presented. Excitations in this system generated by track structure, treated roughly as periodic ones, are often disturbed by track transient imperfections. Obtained solutions are based on Ritz-Galerkin method and then on Hermite’s polynomials application to the problem. Such a model doesn’t require a lot of computing and can be easily adapted e.g. for nonlinear track model. Our approach can take continuous foundation of Winkler or Pasternak layer type, or discrete rail support. For discrete not equi-spaced supports only finite number of them is considered. As the starting point for that solution, the response to Dirac’s impulse is employed. The method described in the paper is relatively efficient (beyond the resonances and near them) to analyse of infinite beams resting on continuous or discrete foundation, even with nonlinear characteristics.
Fabrication of Micro Scale Arrays of Thermoelectric Sensors and Actuators for Cryobiological Applications
Authors: Cygan A. Z. , Prabhakar A. , Podlaha-Murphy E. J. , Murphy M. C. , Devireddy R. V.
Published: April 2008

A device to measure and modulate individual cell temperatures in a tissue culture during cooling and freezing would enhance understanding of tissue freezing. Prefabrication experimentation and modeling were carried out to understand the behavior of the device. Modeling demonstrated that the thermocouples used in the system can be adequately isolated from each other to prevent interference in data collection. Experiments have shown that it is feasible to produce the thermocouples and thermoelectric heaters (TECs) required for fabrication of the device through electrodeposition.
Heat Exchange and Condensation in Reduced Gravity
Authors: Parang Masood , Naumov Viatcheslav
Published: April 2008

The present investigation was sponsored by the NASA Reduced Gravity Student Flight Opportunity Program and was conducted by the University of Tennessee students aboard KC-135 in parabolic flights. The goal of the experiment was to study saturated air-water mixture to simulate the dynamics of condensation and heat exchange in two-phase flows and gain a better understanding of condensation under reduced gravity condition. In the experimental apparatus saturate air/water mixture is pumped through a one-inch cooled horizontal test pipe (condenser). Sets of thermocouples record change of temperature of liquid water, temperature of saturated air across the condenser, and temperature of liquid and fog after the test section. The water temperature measurements indicate lower water temperature and larger exit fog temperature at the condenser exit under reduced gravity as compared with normal gravity results. It was also observed that for relatively small water flow rate and velocity heat exchange between air and water streams was larger for reduced gravity conditions relative to normal gravity conditions.
Theoretical and Experimental Study of a Loop Heat Pipe at Positive Elevation
Authors: Chuang Po-Ya Abel , Cimbala John M. , Brenizer Jack S. , Conroy C. Thomas
Published: April 2008

A loop heat pipe (LHP), which is a two-phase heat transfer device, was studied experimentally and theoretically. The steady-state operating characteristics of a LHP when it is operated at adverse (the condenser is below the evaporator) and zero elevations (the evaporator and the condenser are at the same level) had been studied intensively in the past. However, study of a LHP when it is operated at positive elevation (the condenser is above the evaporator) is still lacking. This paper presents detailed theoretical analysis of the steady-state behavior of a LHP operated at positive elevation. The present analysis agrees with experimental results, and is confirmed by flow visualization images. Testing was performed for a wide range of heat loads (20 W-600 W) at three positive elevations: 25.4mm, 76.2mm, and 127mm. Flow visualization images were taken by neutron radiography when the LHP was operated at 102mm positive elevation.
A 1-D Planar Solid Oxide Fuel Cell Model for Simulation of SOFC-Based Energy Systems
Authors: Sorrentino Marco , Mandourah Ashraf , Petersen Thomas F. , Guezennec Yann G. , Moran Michael J. , Rizzoni Giorgio
Published: April 2008

A one-dimensional steady-state model for planar solid oxide fuel cells (SOFCs) is presented. Appropriately simplified, the model includes sufficient detail for supporting ongoing investigations involving the simulation of SOFC-based advanced energy systems. The presentation focuses on a set of nonlinear equations accounting for conservation of mass and energy along a single SOFC in a co-flow configuration. Electrochemical models also are employed, including one previously used for a zero dimensional approach. The equations are described through a phenomenological approach based on the best recent work in the field and model validation is carried out in two distinct phases using previously published information. Potential areas of application for the model presented are noted.
Directed Assembly of Metal Oxide Nanobelts With Microsystems Into Integrated Nanosensors
Authors: Yu Choongho , Hao Qing , Shi Li , Kang Dae-Jin , Kong Xiangyang , Wang Z. L.
Published: April 2008

Single-crystalline tin dioxide (SnO2) nanobelts have been assembled with microfabricated suspended heaters as low-power, sensitive gas sensors. With less than 4 mW power consumption of the micro-heater, the nanobelt can be heated up to 500°C. The electrical conductance of the heated nanobelt was found to be highly stable and sensitive to toxic and inflammable gas species including dimethyl methyl phosphonate (DMMP), nitrogen dioxide (NO2), and ethanol. The experiment is a step towards the large scale integration of nanomaterials with microsystems, and such integration via a directed assembly approach can potentially enable the fabrication of low-power, sensitive, and selective integrated nanosensor systems.
Biomechanics of Head/Brain Due to Angular Head Acceleration
Authors: Zoghi-Moghadam M. , Sadegh Ali M.
Published: April 2008

In vehicular collisions, contact sports or falls, in addition to blunt impacts, head is subjected to high angular accelerations. This causes relative motion between the brain and skull and an increase in contact and shear stresses in meningeal region which leads to brain injuries. In our previous study Zoghi et al (14), the mechanical role of the fibrous trabeculae and the Cerebrospinal Fluid (CSF) in Subarachnoid space (SAS) were investigated. This is a continuation study of (14) where the attention is focused on the angular acceleration of head rather than blunt impacts. Improved 2-D solid and fluid global models of the head and a local model of the SAS trabeculae were developed. The CSF pressure distribution and the trabeculae deformations were determined. It is expected that in angular acceleration of head, similar to blunt impact, the arachnoid trabeculae reduce the pressure in the CSF and both play a major role in damping the acceleration.
Long-Term Creep and Creep Rupture Behavior of Woven Ceramic Matrix Composites at Elevated Temperatures
Authors: Salekeen Siarajus , Rahman Mohammad M. , Mahfuz Hassan , Jeelani Shaik
Published: April 2008

The strong interest in ceramic matrix composite for high temperature application arises primarily from their ability to retain good creep behavior. The objective of this work is to investigate the creep behavior of quasi-isotropic woven silicon carbide fabric reinforced silicon-nitrogen-carbon (SiC/SiNC) ceramic composite at stress levels which are above and below the monotonic proportional limit strength. Constant-load tensile creep-rupture tests were performed on SiC/SiNC ceramic matrix composite on an Instron 8502 material test system. The creep behavior of SiC/SiNC matrix composites were investigated at various temperatures (700°C and 1000°C) and stress levels (55%, 65% of ultimate strength, σult). The strain vs. time curves consisted of primary and secondary (steady state) creep regions were established. The stress exponent and activation energy of SiC/SiNC ceramic matrix composite were also determined at these temperatures. The creep data followed the traditional power law exhibiting an exponential relationship between creep rate and stress.
Analysis and Characterization of Adhesively Bonded Mg-Steel Lap Joints
Authors: Rahman Niat M. , Mian Ahsan , Newaz Golam M.
Published: April 2008

Dissimilar material joints are of significant interest in automotive applications. An investigation was carried out to determine the peculiarities of an adhesively bonded Mg-steel system for lap shear configuration. Both experimental approach and computational method (FEA) were utilized to evaluate and analyze the Mg-steel bond. The adhesive used was Betamate 1480 — an epoxy based adhesive. The tests were done according to ASTM D 1002-99 method using MTS machine at room temperature. For computational analysis, finite element modeling techniques using ABAQUS processor was utilized. Failure modes were studied for different systems. Results were compared with Mg-Mg and steel-steel systems. It is observed that Mg-Mg balanced system (system with equal adherend or substrate thickness) failed either at interface (adhesive failure) or at substrate and system is flexible with lower failure load. While steel- -steel balanced system failed only at substrate and system is rigid with higher load and lower displacement. Mg-steel system provides flexibility in between them and only adherend failure (either out of plane Magnesium failure or steel-betamate in plane substrate failure) observed. Cohesive failure was not observed in any of the systems. For Mg-Mg, the shear stress distribution in the adhesive is poor (stress distribution is steeper) while for steel-betamate-steel it is much better. The FEA models were compared and rationale was forwarded to assess the failure modes observed in each case.
Applications of VVT and VCR on Fuel Economy Improvement Based Engine Electronic Control
Authors: Ye Zhengmao , Lai Ming-Chia
Published: April 2008

Variable valve timing (VVT) and variable compression ratio (VCR) are two technologies to obtain fuel economy benefit. On the other hand, there is a tradeoff among fuel economy, engine performance and emission levels. Advantages of two technologies vary a lot on different engine operating regions. Recently some experiments are conducted on a Port Fuel Injection (PFI) engine in a city drive cycle to investigate the fuel economy impact from VVT, VCR and the technology integration. The testing results show clearly that the synergy of two technologies has further improved the fuel economy, while suitable operating regions need to be determined where the maximal benefit can be achieved. A typical 1.8L four-cylinder gasoline engine is used for experiments using VVT and VCR technologies for fuel economy improvement. The objective is to create a synergy scheme for the optimal fuel economy performance. The supercharged testing engine with VVT and VCR can implement similar performance to that of a larger replacement engine. The fuel economy optimization problem is simply converted into searching for the lowest engine power output region with respect to the same fuel economy improvement level. These optimal points are useful to determine potential best fuel economy operating regions whether VVT and VCR should be implemented individually or combined together.
A Numerical Technique for Computing Effective Thermal Conductivity of Fluid-Particle Mixtures
Authors: Kumar Satish , Murthy Jayathi Y.
Published: April 2008

Periodic arrays of particles, foams, and other structures impregnated with a static fluid play an important role in heat transfer enhancement. In this paper, we develop a numerical method for computing conduction heat transfer in periodic beds by exploiting the periodicity of heat flux and the resulting linear variation of mean temperature. The numerical technique is developed within the framework of an unstructured finite volume scheme in order to enable the computation of effective thermal conductivity for complex fluid-particle arrangements. The method is applied to the computation of effective thermal conductivity of ordered as well as random beds of spheres and rods. The effect of varying surface area, aspect ratio, volume fraction, orientation, and distribution is studied for various solid-to-fluid conductivity ratios. Unlike classical theories which predict only a dependence on volume fraction, these direct simulations show that aspect ratio, distribution, and alignment of particles have an important influence on the effective thermal conductivity of the bed.
Simulation of Fatigue Crack Growth at Bimaterial Interfaces
Authors: Wang Bo , Siegmund Thomas
Published: April 2008

We present the results of fatigue crack growth simulations in a system with an interface between two elastic-plastic solids of different yield strength. Crack growth is allowed to occur along the direction perpendicular and parallel to the interface. The analysis is conducted by the use of an irreversible cohesive zone model. The outcome of the simulation is in excellent agreement with published experimental data.
The Effect of Boundary Conditions on Nonlinear Vibration and Flutter of Laminated Cylindrical Shells
Authors: Jansen E. L.
Published: April 2008

A nonlinear vibration analysis of cylindrical shells is presented, in which the specified boundary conditions at the shell edges can be satisfied rigorously. The method is based on a perturbation expansion for both the frequency parameter and the dependent variables. The present theory includes the effects of finite vibration amplitudes, initial geometric imperfections and a nonlinear static deformation. Nonlinear Donnell-type equations formulated in terms of the radial displacement W and an Airy stress function F are used, and classical lamination theory is employed. Further, an extension of the theory is presented to analyze linearized flutter in supersonic flow, based on piston theory. The effect of different types of boundary conditions on the nonlinear vibration and linearized flutter behavior of cylindrical shells is illustrated for several characteristic cases.
Advanced Signal Processing Techniques for Multi-Damage Detection With an Improved Embedded Ultrasonic Structural Radar Algorithm and Piezoelectric Wafer Active Sensors
Authors: Yu Lingyu , Giurgiutiu Victor
Published: April 2008

The embedded ultrasonic structural radar (EUSR) algorithm was developed by using piezoelectric wafer active sensor (PWAS) array to detect defects within a large area of a thin-plate specimen. EUSR was verified to be effective for detecting a single crack either at a broadside or at an offside position. However, the damage location was not very precise. This algorithm is improved by using advanced signal processing techniques. The improvement includes: 1) EUSR is able to provide better image of the specimen under monitoring; 2) it is able to detect multiple defects such as several cracks; 3) it is also able to identify different damage types. This paper starts with an introduction of embedded ultrasonic structural radar algorithm. Then the application of using Hilbert transform for extracting the envelopes of the wave packages is discussed. This can eliminate or reduce the effect of side robes so that EUSR produces better images. The improvement of EUSR detectability is concluded through the comparison to the previous results, followed by the experiments to verify the multi-damage detection of EUSR. Finally, we present the results of how EUSR can distinguish different types of damage. This system is implemented by developing a graphical user-friendly interface program in LabView. We conclude with a description of our vision for an even more powerful EUSR for structural health monitoring and embedded nondestructive evaluation.
Side View Imaging for Three Dimensional Microflow Profile Reconstruction
Authors: Yang Sung , Leyton-Mange Jordan , Dong Cheng , Zahn Jeffrey D.
Published: April 2008

A side view imaging system for three dimensional microflow profile reconstruction is successfully developed and demonstrated. Various types of microchannels are prepared and demonstrated to obtain side view images. By combining top view and side view data, the three-dimensional velocity and strain rate profiles are successfully reconstructed.
Investigation of Scalar Measurement Error in Diffusion and Mixing Processes
Authors: Mueschke Nicholas J. , Andrews Malcolm J.
Published: April 2008

In variable density, multi-fluid and reacting flows, a quantitative measure of the degree of molecular mixing is crucial to the development of turbulent transfer and mixing models. In a buoyancy-driven miscible mixing layer, we have found that the initial entrainment of unmixed fluid into the mixing layer causes a decrease in the measure of molecular mixedness at the centerplane of the mixing layer. Following the period of initial entrainment, the fluids within the mixing layer exhibits an increase in the degree of molecular mixing. Characterization of this and other mixing processes require scalar measurement devices with an adequate probe volume size. Spatial averaging, which occurs due to the finite probe volume size, can lead to errors in resolving the density or scalar gradients between pockets of unmixed fluids. Given a probe volume size and a priori knowledge of the functional profile of the diffusion layer being measured, we obtain an estimate for the measurement error due to spatial averaging that has occurred and make corrections accordingly. An analytical model for the measure of scalar mixing is developed as a predictor for the growth of scalar gradients in a variable scalar flow. The model is applied to a buoyancy-driven mixing layer with a Prandtl number of 7.
Structural Health Monitoring of a Nonlinear Aeroelastic System Based on Attractor Analysis
Authors: Yin Shih-Hsun , Epureanu Bogdan I.
Published: April 2008

The dynamic response of a thermo-shielding panel forced by unsteady aerodynamic loads and a archetypal Duffing oscillator are investigated to detect structural damage. A nonlinear aeroelastic model is obtained for the panel by using third order piston theory to model the unsteady supersonic flow which interacts with the panel. To identify damage, we analyze the shape of the attractor of the dynamics of the aeroelastic system and the Duffing oscillator. Measurements are obtained by simulation at only one location along the panel. Damages of various locations, extents and levels are shown to be revealed by the attractor-based analysis. For the panel, the type of damage considered is a local reduction in the bending stiffness. For the Duffing oscillator, variations in the linear and nonlinear stiffnesses and damping are considered as damage. Most of the current studies of such problems are based on linear theories. In contrast, the results presented are obtained using nonlinear dynamics, and have the advantage of an increased accuracy and sensitivity.
Integrating MATLAB and Simulink in an Advanced Engineering Mechanics Course
Authors: Dabney James B. , Ghorbel Fathi H.
Published: April 2008

An advanced engineering mechanics course teaches students to analyze and model a variety of dynamical systems using Newtonian and Lagrangian mechanics approaches. The modeling task typically produces nonlinear differential equations that are best solved numerically. In order to prepare students to competently solve these systems numerically, the students must master a suitable programming environment. This mastery is achieved incrementally throughout the semester. This paper describes a successful approach to developing the necessary programming skills, culminating in a course project in which the students model a complex dynamical system and produce a graphical animation allowing visualization of dynamical behavior. The paper also describes two typical course projects that have been successfully completed by advanced undergraduate and beginning graduate students.