bluuebunny/crossref_metadata_2025 huggingface dataset:
Reformed Fuel and Its Properties, Burning Speeds and Flame Characteristics
Authors: Parsinejad Farzan , Shirk Edwin , Metghalchi Hameed
Published: April 2008

Premixed, lean burn combustion research has been focused for years on extending the lean flammability limit while maintaining both stable ignition and turbulent flame propagation. Burning speed is a fundamental physicochemical property of homogenous fuel/oxygen/diluent mixtures. It determines the rate of energy released during combustion and is of basic importance for developing and testing chemical kinetic models of hydrocarbons. The burning speed and flame structure of blends of reformed fuel and Methane-air mixtures have been studied using two similar constant volumes; a cylindrical vessel with end windows and a spherical chamber. The Experiments were conducted for a range of reformed fuel blends (20–80%) as well as mixture equivalence ratios (0.4–0.6). The burning speed results clearly define the regime of stable flame propagation for equivalence ratio/reformed fuel blend combinations.
Multiscale Control to Meet the Conflicting Nanoscale Performance Requirements
Authors: Shakir Huzefa , Kim Won-Jong
Published: April 2008

In this paper, we consider the problem of designing a multiscale control for plants with conflicting time-domain performance requirements. These results follow from the conventional optimal proportional-integral (PI) control. Four different design methods are proposed: (1) a controller-switch technique which makes use of employing two different controllers designed to meet two different performances and are switched during the course of operation, (2) an integral-reset scheme, which resets the integral term in the control law when the new reference point is reached, (3) controller-switch and integral-reset schemes put together to take benefits of both of them, (4) a model-following approach that uses a dynamic reference model without increasing the overall dimension of the system. The objective of the last scheme is to make the output of the plant track the output of the model as closely as possible. Stability analyses and a comparison between the performances of these methods are given. All these methods give better performances as compared with conventional control schemes. Block diagrams are given and step responses are obtained to demonstrate the proposed methods. A six degrees-of-freedom (DOFs) magnetically levitated (maglev) stage with a second-order pure-mass model has been used to demonstrate the capabilities of the aforementioned control strategies. These strategies are not plant-specific and may be generalized to any higher-order plant.
Statistical Particle Tracking Velocimetry Using Molecular and Quantum Dot Tracer Particles
Authors: Guasto Jeffrey S. , Huang Peter , Breuer Kenneth S.
Published: April 2008

We present the theory and experimental validation of a particle tracking velocimetry algorithm developed for application with nanometer-sized tracer particles such as fluorescent molecules and quantum dots (QDs). Traditional algorithms are challenged by extremely small tracers due to difficulties in determining the particle center, shot noise, high drop-in/drop-out and, in the case of quantum dots, fluorescence intermittency (blinking). The algorithms presented here determine real velocity distributions from measured particle displacement distributions by statistically removing randomly distributed tracking events. The theory was verified through tracking experiments using 54 nm flourescent dextran molecules and 6 nm QDs.
Feedback and Feedforward Control for Electrohydraulic Valve Systems Using a Novel System Identification Technique
Authors: Park Sungbae , Ahmed Jasim , Kojic Aleksandar
Published: April 2008

ElectroHydraulic Valve Systems (EHVS) have the ability to vary valve profiles of internal combustion engines on a per cycle basis, thus allowing one to optimize the combustion process and improve its efficiency and emissions characteristics. Such a capability makes an EHVS system a very suitable actuation mechanism for novel combustion strategies. However, designing a controller which ensures that the EHVS executes the desired valve profiles is challenging due to the required fast response time, the inherent non-linearity of the system, and the time delays associated with the servo valves, actuators and the interconnections. In this paper, we explore a systematic and semi-automatic way to design a controller for an EHVS. The controller has a feedforward and feedback structure. The feedforward controller is obtained by using an on-line system identification scheme, while the feedback controller is based on an off-line system identification model. This procedure is applied successfully to a laboratory EHVS engineered by Team Corporation covering the full range of engine operating speeds from 500 to 4000rpm.
Power and Communication: Solving Power Problems for Collaboration in Globally Distributed Engineering Design Teams
Authors: David Kenneth , Lloyd John R. , Hinds Timothy J.
Published: April 2008

Because outsourcing and offshoring operations entail multi-site operations and inter-organizational alliances, they require effective boundary-spanning partnerships: inter-divisional, inter-organizational, and often, multi-country partnerships. This paper reports a multi-discipline research study—involving engineering, anthropology and telecommunications elements—on dispersed global engineering design teams. A framework involving power, culture, and collaborative activity is introduced. The focus here is on power and communications issues. Co-oriented, collaborative project activity is achieved when power issues are neutralized. When sub-team members perceive inequity, they frequently respond adversely. They may purposely create miscommunications among sub-teams, covertly subvert project goals, or otherwise act in ways that reduce project performance. Outsourcing of engineering design operations is a major challenge for the engineering profession. Outsourcing activity to India and China has increased; educational systems in these countries both improve in quality and augment the quantity of engineers produced. Traditional engineering skills are swiftly becoming a commodity in the global market.
Introducing “Advanced” Tuned Vibration Absorbers in an Undergraduate Vibrations Course
Authors: Koo Jeong-Hoi , Goncalves Fernando , Zhang Hong
Published: April 2008

The primary objective of this paper is to bridge the theory of tuned vibration absorbers (TVA) with the practice of implementing TVAs in systems. Often, the practice of implementing TVAs in systems is a far departure from the theory expressed in many textbooks. These departures are often required in practice to account for the less than ideal conditions that the TVAs will be operating under. Many retrofitted TVAs use “smart” or active materials along with various control techniques to improve the performance of the traditional TVA proposed in textbooks. The intent of the current paper is to demonstrate several of these modern methods of implementing retrofitted TVAs to undergraduate students. The first author introduced the methods in a junior level vibrations course, and is developing a laboratory experiment. Teaching these advanced TVAs to undergraduate engineering students will help them understand how theories learned in class are used in real world problems, and motivate them to explore new fields of research. After introducing a “textbook” vibration absorber theory, this paper describes principles and operations of a new class of vibration absorbers. In reviewing conventional TVAs, students are introduced to many of the engineering challenges encountered in the implementation of TVAs. One such challenge is inevitable off-tuning caused by system parameter changes with time. After identifying many of the challenges associated with the implementation of TVAs, the students are introduced to many modern solutions to these problems. Many of these solutions involve the use of smart materials, such as piezoceramics, magnetorheological fluids, magnetorheological elastomers, shape memory alloys, etc. Through this experience, students are introduced to many smart materials and have the opportunity to see how these smart materials can provide solutions to many engineering challenges and improve existing technologies.
Deformation of a Thermocapillary Driven Liquid Bridge
Authors: Houchens Brent C. , Walker John S.
Published: April 2008

Predicting the free-surface shape of a liquid bridge has been the focus of several recent models of containerless semiconductor crystal-growth methods, such as float-zone processing. We wish to sort out the discrepancies in the predictions of the numerical models by investigating the physics of a simplified system, the half-zone in microgravity. In the absence of gravity, the deformation of the free surface is small. Therefore, we first calculate the flow for a cylindrical melt region, corresponding to a large reference surface tension. This problem is well benchmarked, and the results are in nearly universal agreement. We then investigate a small perturbation of the free-surface shape using the flow calculated for the undeformed liquid bridge. Applying asymptotic expansions, we can predict the leading order of the free-surface velocities and deformation. In this formulation, it is easy to understand the relevance of each term, including the dynamic pressure variation. This solution is also more efficient than the numerical schemes that iterate between the shape of the free surface and the associated flow field. Furthermore, it provides physical insight that is difficult to extract from a purely numerical solution. Conversely, it is an approximation and therefore neglects terms of importance to a highly deformed free surface. Where possible, we will compare the leading-order free-surface shape to that predicted by numerical models, and discuss the advantages and disadvantages of this technique.
CFD Advanced Professional Education via Internet
Authors: Baker A. J. , Grubert M. A. , Ericson S. C. , Orzechowski J. A.
Published: April 2008

The use of computational fluid dynamics (CFD), to better understand/enhance performance of engineered systems design, has deeply penetrated our profession. University academic content now selectively includes comprehensive graduate level courses in CFD. Typically, a large proportion of industry practitioners cannot access this formal content due to remoteness from campus. The newly established UT CFD Laboratory website renders this a non-issue via a fully functional Internet modality for CFD graduate course participation. It presents a totally time-and distance-insensitive fully participatory environment including comprehensive computer laboratory CFD experiments. Successfully completed content is applicable to a MSc degree, to a CFD Certificate or to CEUs when pursued as professional self-study. The scope, organization and illustrations of content of this Internet innovation is presented.
Board Deflection/Strain Instead of Acceleration Measurements for Circuit Board FE Shock Model Validation
Authors: Liang Frank Z. , Williams Richard L. , Hezeltine Wade
Published: April 2008

Modal method and direct time integration analyses are two common FE approaches to simulate circuit board shock response. When using these methods, the model validation depends on comparing the simulated result with either frequency or time domain response. In the past, modal test and analysis has been the final model validation step for using modal method. We believe a shock simulation model should be revalidated following the modal validation, since the modal parameters are global measurements and the second level interconnect (SLI) reliability in shock is more related to its local board bending condition. A revalidation can be done by comparing model simulation acceleration with direct acceleration measurements on the circuit board. However, the board level acceleration may not provide an accurate picture of board level deflection or strain, leading to an incorrect conclusion of the SLI stress predicted by a model. This paper compares the application of acceleration validation method and the method using board deflection and board strain time history to achieve model validation.
Massive Parallel Laser Shock Peening: Simulation, Verification, and Analysis
Authors: Warren A. W. , Guo Y. B. , Chen S. C.
Published: April 2008

Laser shock peening (LSP) is a surface treatment process to improve the surface integrity of metallic components. The nearly pure mechanical process of LSP results in favorable surface integrity such as compressive residual stress and improved surface material properties. Since LSP is a transient process with laser pulse duration time on the order of 40 ns, real time in-situ measurement of laser/material interaction is very challenging, if not impossible. A fundamental understanding of laser/material interactions is essential for LSP planning. Previous finite element simulations of LSP have been limited to a single laser shock location for both two and three dimensional modeling. However, actual LSP are performed in a massively parallel mode which involves almost simultaneous multi-laser/material interactions in order to induce uniform compressive residual stress across the entire surface of the workpiece. The massively parallel laser/material interactions have a significant compound/interfering effect on the resulting surface integrity of the workpiece. The numerical simulation of shock pressure as a function of time and space during LSP is another critical problem. The purpose of this paper is to investigate the effects of parallel multiple laser/material interactions on the stress/strain distributions in the workpiece during LSP of AISI 52100 steel. FEA simulations of LSP in single and multiple passes were performed with the developed spatial and temporal shock pressure model via a subroutine. The simulated residual stresses agree with the measured data in nature and trend, while magnitude can be influenced by the interactions between neighboring peening zones and the locations of residual stress measurement. Design-of-experiment (DOE) based simulations of massive parallel LSP were also performed to determine the effects of laser intensity, laser spot size, and peening spacing on stresses and strains. Increasing the laser intensity increases both the stress magnitude and affected depth. The use of smaller laser spot sizes decreases the largest magnitude of residual stress and also decreases the depth affected by LSP. Larger spot sizes have less energy attenuation and cause more plastic deformation. Spacing between peening zones is critical for the uniformity of mechanical properties across the surface. The greatest uniformity and largest stress magnitudes are achieved by overlapping of the laser spots.
A Finite Element Analysis Based Compliance Method Coupled With Wet Etching to Determine Residual Stress in High Speed Milling
Authors: Ammula S. C. , Guo Y. B. , Barkey M. E.
Published: April 2008

High speed milling (HSM) is widely used in automotive and aerospace industries in fabricating mechanical components from high strength aluminum and other alloys due to high productivity and good surface finish. HSM induced residual stresses may significantly impact the fatigue life and corrosion resistance of the machined components. Traditional methods of residual stress (RS) measurement, such as hole drilling, X-ray diffraction, and neutron diffraction, are very time consuming and expensive, especially for the shallow subsurface (usually <100 μm) of a machined component. The compliance method provides a convenient alternative to these approaches to determine the residual stress distributions in the subsurface. However, the compliance method using wire EDM is prone to experimental errors. In addition, the traditional approach to calculate compliance function is very complex. This paper presents a new wet etching approach to obtain strains as a function of slot depth introduced in the subsurface. The strain readings were collected from a strain gauge mounted on the specimen surface near the slot edge. The compliance function can be conveniently calculated by simulating slot cutting using the finite element method via a Legendre polynomial subroutine as the applied load. These calculated compliance functions and measured strain values at different depths were used as inputs into a program to calculate residual stress. This leads to much a faster and less expensive method of determining residual stresses when compared with the traditional methods of residual stress determination. The capability of this new approach was demonstrated by high speed milling 6061-T651 and 7050-T7451 aluminum alloys. A design of experiment (DOE) method was adopted to conduct fifty-four cutting conditions with three levels of cutting speed, feed rate, and depth of cut. Residual stress profiles with twelve data points with spatial resolution as small as 1 μm in the subsurface were then obtained using this new approach. Residual stress sensitivity to cutting conditions was investigated. In addition, subsurface microstructure and microhardness were characterized.
Single-Step, Integrated Assembly and Encapsulation of Microfluidic Bubble Generator
Authors: Geiger Emil J. , Lippmann Julian M. , Frank Jeremy A. , Pisano Albert P.
Published: April 2008

This paper describes a single-step method for assembling and encapsulating a microbubble chamber in which injection-molded plastic secures the fluidic and electrical interconnects. All of the necessary components for the chamber are loose assembled in a plastic-injection mold and subsequently packaged, encapsulated, and sealed in one molding step. These components include a silicon/Pyrex® bubble chamber, copper electrical leads, and small-gauge stainless steel fluidic headers. This approach delivers a fully integrated microbubble chamber with 1) zero dead volume, 2) low electrical contact resistance (<1 Ohm), 3) low compliance, in-plane fluid interconnects and 4) small overall dimensions (7.5 mm × 4 mm × 3 mm) conforming to the Dual In-Line Package (DIP) standard, Fig 1.
Adiabatic Shear Modeling and Its Influence on Machining Simulations: BCJ vs. JC Model
Authors: Wen Q. , Guo Y. B. , Woodbury K. A.
Published: April 2008

The understanding of mechanical behavior in machining is critical to analyze and design a process. It is well known that work materials experience large strains, high strain rates, high temperatures, and complex loading histories. Adiabatic or quasi-adiabatic condition is an important feature of material deformations in machining ferrous alloys. The problem of how to accurately model the mechanical behavior including the adiabatic effect is essential to understand a machining process. Several constitutive equations such as the simple power law model, Johnson-Cook (JC) model, and other models have often been used to approximate flow stress in machining analysis and simulations. The JC and other empirical or semi-empirical models lack mechanisms in incorporating complex loading effects. The internal state variable plasticity Baumann-Chiesa-Johnson model (BCJ model) has been shown to incorporate loading histories as well as state variables. In this study, we have determined the material constants of AISI 52100 steel (62 HRc) for both the JC and BCJ models using the same baseline stress-strain data. The material constants were obtained by fitting the JC and BCJ models to these test data at different strains, strain rates, and temperatures using nonlinear least square methods. Both models are capable of modeling strain hardening and thermal softening phenomena. However, the BCJ model can also accommodate the adiabatic effect, while the JC model is basically isothermal. Orthogonal cutting tests and FEA simulations, based on the design-of-experiment method, were performed using the cutting tool with a 20° chamfer angle. The predicted saw-tooth chip morphology and dimensions using the BCJ model are consistent with the measured chips in the cutting tests, while the JC model yielded discontinuous chips. In addition, the BCJ model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.
Analytical Dynamics of a Piecewise Linear Friction Oscillator Under a Periodic Excitation
Authors: Luo Albert C. J. , Zweigart Patrick
Published: April 2008

This paper presented a methodology to determine the analytical dynamics of the periodically forced friction oscillator. The friction force is modeled by a piecewise linear, kinetic friction model with the static force. The input and output force concepts in the vicinity of the discontinuous friction force boundary are introduced. The force criteria for the onset and vanishing of stick and non-stick motions are presented through the input and output forces. The periodic motion of such an oscillator is determined through the corresponding mapping structure. The local stability of the periodic motions is presented. Illustrations of the periodic motions in such a piecewise friction model are given for better understanding the stick motion with static friction. The force responses are presented, which agreed very well with the force criteria.
The Scattering Field of SH-Wave in Half-Space With a Semi-Cylindrical Hill and a Horizontal Circular Tunnel
Authors: Wang Guoqing , Dai Liming , Liu Diankui
Published: April 2008

The scattering field of SH-wave in a half-space with a semi-cylindrical hill and a subsurface horizontal hole is studied in the present research by utilizing a complex function and the moving-coordinate method. Based on the concept of ‘conjunction,’ the domain considered is divided into two subdomains. The first subdomain is a cylindrical one which includes the surface of the hill, while the rest is the second subdomain. In the cylindrical subdomain, a standing wave function is constructed which automatically satisfies the zero-stress condition at the hill surface and arbitrary-stress condition at the other part of the circular subdomain. For the second subdomain, which contains a semi-cylindrical canyon and a subsurface hole, a scattering wave function is assumed, which satisfies the zero-stress condition on the horizontal surface. By employing the moving-coordinate method, the solutions of the mathematical model established for the SH-wave can be obtained with the satisfaction of the continuous conditions of stress and displacement across the junction interface together with the zero-stress condition at the surface of the tunnel. The solutions such obtained consist of a series of infinite linear algebraic equations, which can be solved numerically with consideration of the first finite terms corresponding to the frequencies of the wave. For demonstrating the application of the model developed, the displacements of the horizontal and semi-cylindrical hill surfaces are quantified with different properties of wave and geometry parameters.
A Reduced 1&1D Model for Optimization Analysis of a PEM Fuel Cell
Authors: Ambu¨hl D. , Anguiano N. , Sorrentino M. , Guezennec Y. , Mazumder S. , Rizzoni G.
Published: April 2008

An application-oriented steady-state PEMFC model is presented. The model is computationally fast enough to allow for applied investigations such as optimizations and sensitivity analyses but is detailed enough to observe local flow phenomena such as membrane flooding. The model resolves parameters along the flow channel and incorporates a separate membrane model. Contrary to other existing 1-D models of PEMFCs, water content within the membrane is not assumed to follow a linear profile between anode and cathode, but is resolved across membrane thickness and solved off-line for the entire domain of possible water-content boundary conditions. Co-flow and counter-flow topologies have been investigated from a end-user perspective. In addition, the model has been extended with hydrogen recirculation as well as air humidification with an electro-chemically passive cell. The effects of the anode and cathode humidification are investigated based on a sensitivity analysis. Systematic optimizations on operating conditions are also carried out for the different topologies to maximize efficiency such that no flooding occurs.
The Tribological Characteristics of the Surface Coatings on Rotary Compressor Vane in Carbon Dioxide Environment
Authors: Oh Se-Doo , Lee Young-Ze
Published: April 2008

The carbon dioxide is investigated as an alternative refrigerant to replace HFC refrigerants in refrigerators and air conditioning systems due to the environmental concerns. Because new compressors with the carbon dioxide are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressors, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN, WC/C and two types of nitridings, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-disk type sliding tests were carried out under the various sliding speeds, normal loads, and carbon dioxide pressures with an exclusive high pressure wear tester. From the tests wear volume of vane surfaces applied various coatings were compared. During the tests coefficients of friction and surface temperatures were monitored. Test results showed that WC/C coatings showed good tribological properties. TiN and CrN coated vanes showed good wear resistance properties but produced high friction.
The Discontinuous Finite Element Method for Polycrystalline Grain Growth With Convection
Authors: Ai Xin , Shu Y. , Li Ben Q.
Published: April 2008

In this paper, a numerical study of the convection effect on polycrystalline grain growth is performed. The coupled two-dimensional polycrystalline phase field model, energy equation and Navier-Stokes equations are solved, which is based on the discontinuous Galerkin finite element method. The numerical algorithm is validated, and the effect of the external convection flow is examined for growth of grains with different orientation. Results show that the forced convection flow affects the phase and orientation field distribution by changing the temperature gradient in the solid/liquid interface.
Development of Hydraulic-Electric Power Unit for Mobile Robots
Authors: Raade Justin W. , Amundson Kurt R. , Kazerooni H.
Published: April 2008

Energetic autonomy of a hydraulic-based mobile robot requires a power source capable of both hydraulic and electrical power generation. The hydraulic power is used for locomotion and the electric power is used for the control computer, sensors and other peripherals. In addition, the power source must be lightweight and quiet. This study presents several designs of internal combustion engine-based power units. Each power unit is evaluated with a Ragone plot which shows its performance over a wide range of operation times. The best-performing design of the hydraulic-electric power units (HEPU), based upon the Ragone plot analysis, is described in detail. This HEPU produces constant pressure hydraulic power and constant voltage electric power. The pressure and voltage are controlled on board the power unit by a computer. A novel characteristic of this power unit is its cooling system in which hydraulic fluid is used to cool the engine cylinders. The prototype power unit weighs 27 kg and produces 2.3 kW (3.0 hp) hydraulic power at 6.9 MPa (1000 psi) and 220 W of electric power at 15 VDC.
Hybrid Computing Techniques for Collaborative Control of UCAVs
Authors: Hoover Randy C. , Schoen Marco P. , Naidu D. Subbaram
Published: April 2008

This paper presents a new approach to collaborative control of multiple Uninhabited Combat Aerial Vehicles (UCAVs) using hybrid soft and hard computing techniques. The approach develops a hierarchical architecture, which consists of four separate layers. The first layer describes the navigational system responsible for mission planning/re-planning, target priority, target distribution among individual UCAVs, and communication/collaboration between all UCAVs in the battlefield. The second layer describes the sensor fusion/definition on each individual UCAV. The third layer describes a fuzzy interpretation system (FIS) in which static and dynamic threat avoidance, and real-time path planning are outlined. The fourth and final layer contains the individual UCAV plant dynamics, autopilot, and navigation subsystem which accepts heading, altitude, and velocity commands. Extensive simulations are given to validate the proposed approach for any number of UCAVs flying in the battlefield.
Assessment of Steady State PSP and Transient Ir Measurement Techniques for Leading Edge Film Cooling
Authors: Gao Zhihong , Wright Lesley M. , Han Je-Chin
Published: April 2008

Film cooling is commonly used on the leading edge of turbine blades to protect the blade surface from hot mainstream gases in the turbine. Obtaining detailed film cooling effectiveness distributions on the leading edge can be challenging. This paper considers two measurement techniques which can be applied to the leading edge (modeled by a cylinder) to obtain detailed distributions of the film effectiveness. A steady state pressure sensitive paint (PSP) technique and a transient infrared (IR) thermography technique are used to obtain detailed film cooling effectiveness distributions on the cylinder. The cylinder, 7.62 cm in diameter, is placed in a low speed wind tunnel, with the mainstream flow having a Reynolds number of 100,900 (based on the cylinder diameter). The cylinder has two rows of film cooling holes located at ±15° from the cylinder’s stagnation line. The pitch-to-diameter ratio of the film holes is 4, and holes are inclined 30° in spanwise direction. PSP continues to show promise for film cooling effectiveness measurements. Detailed distributions can be obtained near the film cooling holes because this technique relies on mass transfer rather than heat transfer. In order to reduce the error caused by conduction in heat transfer experiments, transient measurement techniques are favorable. Transient IR measurements are taken, and film cooling effectiveness is determined on the cylinder’s surface. Although the effect of conduction is reduced with the transient IR technique (compared to a steady state heat transfer experiment), heat conduction through the cylinder has not been eliminated (or even minimized). Without correction, the results obtained from transient heat transfer experiments must be used cautiously. For this reason, PSP is developing a niche within the gas turbine community for detailed film cooling effectiveness measurements.
Evaluation of Creep Properties in Soldering Ball by Nanoindentation Creep
Authors: Shibutani Tadahiro , Yu Qiang , Shiratori Masaki
Published: April 2008

In this paper, the behavior the behavior of creep deformation in low melting point alloy during a nanoindentation test was examined. Nanoindentation creep test was performed for eutectic tin-lead solder ball. Estimated creep exponent from the relationship between hardness and indenter dwell-time decreases as a function of time. The morphology of indented area shows that the transition from the deformation due to the tip in the early stage to another one in the last stage. Each grain near the indenter tip was transformed in the last stage. Stress analysis using a finite element method reveals that relaxation of equivalent stress progresses rapidly and the residual hydrostatic stress is dominant. Then, the gradient of the residual hydrostatic stress affects the chemical potential on grain boundaries and diffusion creep is activated. Therefore, the transition from the power-law creep to diffusion creep takes place during the nanoindentaion creep.
Flow Structure and Enhanced Heat Transfer in Channel Flow With Dimpled Surfaces: Application to Heat Sinks in Microelectronic Cooling
Authors: Silva Carlos , Marotta Egidio , Fletcher Leroy
Published: April 2008

The use of dimple technology for improvement in friction factors and enhancement of heat transfer has been attracting the attention of many scientists and engineers. Numerical and experimental studies have shown there is a positive improvement (two-fold on average) in Nusselt number when dimpled surfaces are compare to flat plates, and this improvement is achieved with pressure drop penalties that are small when compared to other more intrusive types of turbulence promoters. When arrays of specific dimple geometry are used, pressure drop penalties are roughly equivalent to the heat transfer improvement. This, at least theoretically, will enable the design of smaller heat transfer devices such as heat sinks, which are especially appealing in those applications where size is an important design factor. A literature review of numerical modeling and experiments on flow over dimpled surfaces was performed, and key parameters and flow structure were identified and summarized. With these premises, a numerical model was developed. The model was validated with published experimental data from selected papers and fine-tuned for channel flow within the laminar flow regime. Subsequently, the model was then employed for a specific application to heat sinks for microelectronic cooling. This paper, then, provides a comparative evaluation of dimple technology for improving heat transfer in microelectronic systems.
Temperature Nonuniformity During Applying Dynamic Infrared Thermography for Tumor Detection: Impact of Large Vessels
Authors: Deng Zhong-Shan , Liu Jing
Published: April 2008

During applying infrared thermography for detection of superficial tumors, the presence of large blood vessels transmitting through the detected region and carrying blood at the systemic temperature can be an important source of temperature non-uniformity and possible misdiagnose. However, such important issue in non-invasive thermal diagnostics has received few attentions up to now. In this study, two typical vascular models are applied to probe into the impact of large blood vessels on the skin temperature profiles during applying both steady-state and dynamic infrared thermography. The results indicate that the large vessels close to the disease region can produce significant effects to the thermal images at skin surface, and that without carefully considering the impact of large vessels, both false negative and false positive diagnoses may be made. This study is expected to help realize a more accurate and quantitative non-invasive diagnoses using infrared thermography in the presence of large vessels.
Design and Validation of a 30,000 kg Heavy Goods Vehicle Using LS-DYNA
Authors: Atahan Ali O. , Bonin Guido , El-Gindy Mustafa
Published: April 2008

Extraordinary developments in virtual crash testing research have been achieved during the past decade. Advancements in hardware and software technology along with improvements in computation mechanics and increased number of full-scale crash tests contributed positively to the development of more realistic finite element models. Use of complex finite element codes based on computational mechanics principles allowed the virtual reproduction of real world problems. Regarding roadside safety, the design phase was, until now, based on the use of simplified analysis, unable to describe accurately the complexity of vehicle impacts against safety hardware. Modeling details, such as geometry, constitutive laws of the materials, rigid, kinematic and other links between bodies, definition and characterization of contact surfaces are necessary to build an accurate finite element model for an impact problem. This set of information is needed for each different body involved in the event; making the development of a complete model very much demanding. Once a part (subset) of the entire model has been accurately validated against real experimental data, it can be used again and again in other analogous models. In this paper, finite element model of a unique Heavy Goods Vehicle (HGV) was developed and partially validated using actual crash test data. Development of this particular vehicle model was important since this vehicle is extensively used in Europe to test the structural adequacy of high containment level (H4a) safety barriers according to EN 1317 standard. The HGV model studied reproduces a FIAT-IVECO F180 truck, a vehicle with 4 axles and a mass of 30,000 kg when fully loaded. The model consisted of 12,337 elements and 11,470 nodes and was built for and is ready to use with LS-DYNA finite element code from Livermore Software Technology Corporation. Results of the validation study suggest that the developed HGV model shows promise and can be used in further studies with confidence. Improvements such as, steering mechanism in front axes and suspension system is currently underway to make model more realistic.
Investigation on Dynamic Interaction Between Wagon and Randomly Irregular Rail Track
Authors: Durali Mohammad , Jalili Mohammad Mahdi
Published: April 2008

Rail profile irregularities are one of the main vibration sources to vehicle and track. In this article a dynamic model of wagon, rail track and its substrate is developed to examine the vertical interaction of the rail track and the wagon system due to random irregularities of track vertical profile. The model consists of a wagon with body, two bogies and four wheels having 21 degrees of freedom. The rail system is treated as a Timoshenko beam supported by sleepers, ballast, subballast, and subgrade. The rail irregularities are assumed to be stationary random and ergodic processes in space, with Gaussian amplitude probability densities and zero mean values. To determine rail-wheel contact forces, Hertzian nonlinear contact theory has been used. The interaction forces between the vehicle and the rail and the vertical acceleration generated in the wagon body due to random irregularities of the track vertical profile with different track grades for different train speeds have been simulated by this model. The results are compared to previous works in the literature.
A Heuristic Model for Estimating the Lowest Gap of Locally Resonant Phononic Crystals
Authors: Liu Yaozong , Shao Lihui , Wang Gang , Yu Dianlong
Published: April 2008

The influences of the constituent material parameters of the three-dimensional locally resonant phononic crystal on the lower and upper edge frequencies of its lowest gap are investigated with the Multiple-scattering theory. It is found that the frequency dependence on those parameters can be well reproduced by a simple mass-spring model, which manifests the physical essence of the resonance modes determining the edge frequencies of the gap. Since the equivalent mass and stiffness of the model can be determined from the material parameters and structure size in one unit cell, the lower and upper edge frequencies of the lowest gap of locally resonant phononic crystals can be estimated from this model analytically. Comparison between the analytical estimations and the numerical results calculating with multiple scattering method shows very good agreement. The proposed heuristic model lends itself to understand the locally resonant mechanism more clearly. The frequency estimating formulas induced from the model allow one to predict the edge frequencies of the lowest gap, which simplifies the design process of locally resonant phononic crystals.
Vortex Breakdown in a Cylindrical Enclosure With a Rotating Lid
Authors: Molki Majid , Olcay Ismail Hakan
Published: April 2008

A computational research was conducted to explore the nature of the flow in a cylindrical enclosure with a rotating lid. The aspect ratio (AR) of the cylinder used in this research was maintained at 1.5 and 2.5, and the Reynolds number (Re) ranged from 990 to 2200. The three-dimensional Navier-Stokes equations were solved by the finite volume technique. Mesh adaptation was used to improve the quality of the mesh and computations. The results for (AR, Re) = (1.5, 1290) and (2.5, 2200) indicated the existence of one and two vortex breakdown bubbles along the axis of the cylinder, respectively. The results also showed that fluid spirals downward along the cylindrical wall and moves slowly inward towards the axis. This spiral motion was intensified at higher values of the Reynolds number. Comparison with experimental data indicated an excellent agreement. The vortex breakdown and the flow patterns predicted by this work are consistent with those reported in the existing literature.
Synthesis of Carbon Nanotubes on a Moving Substrate by Laser-Induced Chemical Vapor Deposition
Authors: Kwok Kinghong , Chiu Wilson K. S.
Published: April 2008

An open-air laser-induced chemical vapor deposition technique has been successfully used to rapidly deposit pillars of carbon nanotube forest on a moving glass substrate. A CO2 laser is used to heat a traversing fused quartz rod covered with metal particles inside a hydrocarbon environment. Pyrolysis of hydrocarbon precursor gas occurs and subsequently gives rise to the growth of multi-wall carbon nanotubes on the substrate surface. The experimental results indicate that nanotube growth kinetics and microstructure are strongly dependent on the experimental parameters such as laser power. The typical deposition rate of carbon nanotubes achieved in this study is over 50 μm/s, which is relatively high compared to existing synthesis techniques. At high power laser irradiation, carbon fibers and carbon film are formed as a result of excessive formation of amorphous carbon on the substrate. High-resolution transmission and scanning electron microscopy, and x-ray energy-dispersive spectrometry are used to investigate the deposition rate, microstructure and chemical composition of the catalytic surface and the deposited carbon nanotubes.
Modeling of Crack Growth in Ductile Solids
Authors: Gao Xiaosheng , Kim Jinkook
Published: April 2008

In this study, two types of approaches are considered to model material failure process and crack propagation in ductile solids. In the first approach, voids are considered explicitly and modeled using refined finite elements. A distinct advantage of this approach is the exact implementation of the void growth behavior. In order to establish crack advance, a failure criterion for the ligament between a void and the crack tip is required, which can be obtained by conducting systematic finite element analyses of the void-containing, representative material volume subjected to different macroscopic stress states. In the second approach, voids are considered implicitly by using porous plasticity models. This approach is attractive for simulation of extensive crack growth because detailed modeling of each individual void is avoided. As an example, a numerical approach is proposed to predict ductile crack growth in thin panels of a 2024-T3 aluminum alloy, where a porous plasticity model is used to describe the void growth process and the material failure criterion is calibrated using experimental data. The calibrated computational model is applied to predict crack extension in fracture specimens having various initial crack configurations. The numerical predictions agree very well with experimental measurements.
Rotary Ultrasonic Machining of Titanium Alloy: A Feasibility Study
Authors: Churi N. J. , Li Z. C. , Pei Z. J. , Treadwell C.
Published: April 2008

Due to their unique properties, titanium alloys are attractive for some unique applications especially in the aerospace industry. However, it is very difficult to machine these materials cost-effectively. Although many conventional and non-conventional machining methods have been reported for machining them, no reports can be found in the literature on rotary ultrasonic machining of titanium alloys. This paper presents an experimental study on rotary ultrasonic machining of a titanium alloy. The tool wear, cutting force, and surface roughness when rotary ultrasonic machining of the titanium alloy have been investigated using different tool designs and machining conditions. The results are compared with those when machining the same material with diamond grinding.
Numerical Simulation of Turbid-Density Current Using v2 – f Turbulence Model
Authors: Mehdizadeh A. , Firoozabadi B. , Farhanieh B.
Published: April 2008

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2 – f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2 – f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2 – f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current, (its critical Reynolds no. is about 1000), the κ - ε model, which was standardized for high Reynolds number and isotropic turbulence flow, cannot simulate the anisotropy and non-homogenous behavior near wall. In this study, turbidity current with uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with experimental data sets. Moreover, results have been compared with the standard κ - ε turbulent model. Results show that the κ - ε model has the poor result on this current. In addition, results show that the coarse particles settle down rapidly and make the higher deposition rate. The deposition of particles and the effects of their fall velocity on concentration distribution, height of body, and entrainment coefficient are also investigated.
High Resolution Simulations of Particle-Driven Gravity Currents
Authors: Meiburg Eckart , Blanchette F. , Strauss M. , Kneller B. , Glinsky M. E. , Necker F. , Ha¨rtel C. , Kleiser L.
Published: April 2008

High-resolution simulations of particle-driven gravity currents are presented. The study concentrates on dilute flows with small density differences between particle-laden and clear fluid. Moreover, particles are considered which have negligible inertia, and which are much smaller than the smallest length scales of the buoyancy-induced fluid motion. The governing equations are integrated numerically with a high-order mixed spectral/spectral-element technique. In the analysis of the results, special emphasis is placed on the sedimentation and resuspension of the particles, and on their feedback on the flow dynamics. Resuspension is modeled as a diffusive flux of particles through the bottom boundary. The conditions under which turbidity currents may become self-sustaining through particle entrainment are investigated as a function of slope angle, current and particle size, and particle concentration.