bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple Formulae for the Stress Concentration Factor Around Spherical Cavities of Various Geometries at Surface of Well Casings and Pipelines
Authors: Sun Kai , Guo Boyun , Ghalambor Ali
Published: April 2008

Well casings and pipelines in the petroleum industry are subject to severe corrosion because of their exposure to seawater and corrosive fluids that are transported. Corrosion develops pits and cavities at the surface of these structures. Under operating conditions, stress concentration around the cavities determines strength degradation of the structures. The strength deterioration can significantly shorten the life; even cause failure of the structure if this effect is not considered during the design stage. It is highly desirable to know the stress concentration factor (SCF) for both designing and evaluating tubular structures. Despite the rapid development of various numerical methods such as the finite element method, SCF analysis with any numerical method is still a tedious and time-consuming task for ordinary engineers. This paper derives simple formulae for SCF around cavities of various geometries at the surface of tubular structures. The cavity geometries considered include shallow-spherical (depth is less than the open radius), medium-spherical (depth is equal to the open radius), and deep-spherical (depth is greater than the open radius) cavities. SCF graphs are generated and results of sensitivity analyses are presented in this paper. These SCF formulae and graphs can be used in both designing and evaluating tubular structures with spherical cavities.
Characteristics of Partially Premixed Elliptic Burner Flames in Coflow-Velocity Air Streams
Authors: Hariharan P. , Gollahalli S. R.
Published: April 2008

This paper presents the results of an extension of the previous study where the effects of jet equivalence ratio and burner geometry on the characteristics of partially premixed propane/hydrogen/air flames at a coflow air velocity of 3 m/s were presented. The results here pertain to the experiments where the coflow velocity was doubled to understand the effects of coflow. Two different burner geometries (Circular, and 3:1 aspect ratio-AR elliptical burners) were used in the experiments with circular burner flames as baseline condition. During the study, the exit velocity was held constant at 20 m/s for all conditions. Stability tests indicated that circular burner flames were more stable than the 3:1AR elliptical burner flames at quiescent conditions. At 6 m/s coflow air velocity, stability of both the circular and the 3:1AR elliptic flames was enhanced. Circular burner flames were longer than 3:1AR elliptical burner flames. Introduction of 6 m/s coflow air velocity reduced the flame height. Global NO and CO emission indices decreased considerably after the introduction of coflow air in both burners. Peak temperature of circular burner flames was higher than that of 3:1AR elliptic burner at all conditions. Inflame concentration measurements were also taken in near-burner (25% flame height), midflame (50% flame height) and far-burner (75% flame height) regions.
Experimental Investigation of Perforated Plate Turbulent Flow Past a Solid Sphere
Authors: Tyagi Himanshu , Liu Rui , Ting David S.-K. , Johnston Clifton R.
Published: April 2008

As the first stage of a comprehensive investigation of turbulence effect on the aerodynamics of sphere, the effect of freestream turbulence on the wake generated behind a sphere is investigated in this study. A 10 cm (4 in) diameter plastic sphere was placed in a wind tunnel of cross section 75 cm by 75 cm. The freestream turbulence was generated by fixing a perforated plate to the entrance of the test section. The wake was characterized using a normal constant-temperature hotwire at 30D, 40D and 50D (11.25d, 15d & 18.75d respectively) downstream of the sphere (where D = 3.75 cm is the diameter of the perforated plate hole, and d is the diameter of the sphere). The Reynolds number of the flow, based on the mean velocity and the diameter of the sphere, was 6.6 × 104. Based on the instantaneous velocity measurement, Kolmogorov length scale, integral length scale and relative turbulence intensity in the wake were deduced.
Temperature-Dependent Luminescence Quenching in Random Nano Porous Media
Authors: Ruan Xiulin , Kaviany Massoud
Published: April 2008

The luminescence quenching of a random, crystalline one-dimensional model porous medium doped with rare-earth elements, is analyzed by considering the transport, transition, and interaction of the fundamental energy carriers. The quenching in nano porous media is enhanced compared to a single crystal, due to multiple scattering, enhanced absorption, and low thermal conductivity. The coherent wave treatment is used to calculate the photon absorption, in order to allow for field interference and enhancement. The luminescent and thermal emission is considered as incoherent. The luminescence quenching and non-linear thermal emission, occurring with increasing irradiation intensity, are predicted.
Thermal Control of Laser Powder Deposition: Heat Transfer Considerations
Authors: Langerman Michael A. , Buck Gregory A. , Korde Umesh A. , Kalanovic Vojislav D.
Published: April 2008

Laser based solid free-form fabrication is an emerging metallurgical forming process aimed at rapid production of high quality, near net shape products directly from starting powders. Laser powder deposition shares, with other free-form technologies, the common characteristic that part fabrication occurs directly from a 3-D computer aided design (CAD) model. The microstructure evolution and resulting material properties of the component part (strength, ductility, etc.) fabricated using laser deposition are dependent upon process operating parameters such as melt pool size, laser power, head (manipulator) speed, and powder flow rate. Presently, set points for these parameters are often determined through manual manipulation of the system control and trial and error. This paper discusses the development of a path-planning, feed-forward, process-driven control system algorithm that generates a component part thermal history within given constraints, thereby assuring optimal part quality and minimizing final residual stresses. A thermal model of the deposition process drives the control algorithm. The development of the thermal model is the subject of this paper. The model accounts for temperature-dependent properties and phase change processes. Model validation studies are presented including comparisons with known analytic solutions as well as comparisons with data from experiments conducted in the laser laboratory at SDSM&T.
Development and Testing of a Small-Scale Collins Type Cryocooler
Authors: Hannon C. L. , Krass B. J. , Gerstmann J. , Chaudhry G. , Brisson J. G. , Smith J. L.
Published: April 2008

Future spacecraft cooling and sensing systems will require advanced multi-stage cryocoolers capable of providing continuous cooling at multiple temperature levels ranging from 10K to 95K. A multi-stage 10K cryocooler is under development that applies modern microelectronic sophistication to achieve high efficiency in a reliable, compact design. The cryocooler is based upon a novel modification of the Collins cycle, a cycle commonly used in many high-efficiency terrestrial cryogenic machines. Innovations of the design include floating piston expanders and electromagnetic smart valves, which eliminate the need for mechanical linkages and thereby reduce the input power, size, and weight of the cryocooler in an affordable modular design. The floating piston expander and smart valves have been successfully developed in room temperature experiments using a series of proof-of-concept component prototypes. These experiments have resulted in a new warm-end configuration with improved expansion power dissipation and a new cryogenic valve design that reduces expander clearance volume and improves cold-end integration. A sophisticated LabView based control algorithm was developed over the course of the room temperature experiments that enables electronic control of the expansion cycle. Software based control will enable variable valve timing and adaptive control logic. This will result in a cryocooler with rapid cool-down and transient response capabilities as well as the ability to operate at high efficiency at arbitrary steady state load points. In parallel to this effort, a manufacturing method was developed to enable production of very long continuous lengths of small bore finned tubing. This tubing is used in the highly effective recuperative heat exchanger associated with each stage of the cryocooler. An engineering prototype has been designed that integrates the floating piston expander and recuperative heat exchanger as a functional cryocooler. The engineering prototype has been assembled and is currently undergoing development testing. This paper will present the results of the room temperature component development testing, the design of the engineering prototype, the results of initial engineering prototype development testing, and the direction of future development.
Thermal Characterization of an All-Active Microring Resonating Laser
Authors: Fleischer Amy S. , Troppenz Ute , Hamacher Michael , John Werner
Published: April 2008

Active microring optical devices are promising candidates for use in next generation optical signal processing and sensor products. In this design, an InP based microring laser is vertically coupled to a passive feeding waveguides using a waferbonding technology. The vertical coupling is expected to detrimentally affect the operating temperature and device performance through the low thermal conductivity of the bond material. Thus, a thermal analysis is undertaken in the design stage to better understand the implications of this fabrication process. A thermal analysis of a basic microring resonator of 50 μm radius and 100 mW power dissipation is presented and thermal design variations are discussed.
HP-Adaptive Time-Discontinuous Galerkin Finite Element Methods for Time-Dependent Waves
Authors: Subbarayalu Sethuramalingam , Thompson Lonny L.
Published: April 2008

hp-Adaptive time-discontinuous Galerkin methods are developed for second-order hyperbolic systems. Explicit a priori error estimates in terms of time-step size, approximation order, and solution regularity are derived. Knowledge of these a priori convergence rates in combination with a posteriori error estimates computed from the jump in time-discontinuous solutions are used to automatically select time-step size h and approximation order p to achieve a specified error tolerance with a minimal number of total degrees-of-freedom. We show that the temporal jump error is a good indicator of the local error, and the summation of jump error for the total interval is good indicator for the global and accumulation errors. In addition, the accumulation error at the end of a time-step can be estimated well by the summation of the local jump error at the beginning of a time-step provided the approximation order is greater or equal to the solution regularity. Superconvergence of the end points of a time-step for high-order polynomials are also demonstrated.
Investigation of the Complex Two Degrees of Freedom Systems for Force Limited Vibration
Authors: Cote Andre , Sedaghati Ramin , Soucy Yvan
Published: April 2008

Force Limited Vibration (FLV) Testing developed at Jet Propulsion Laboratory offers many opportunities to decrease the overtesting problem associated with traditional vibration testing. Among the force limited vibration methods, the complex two degrees of freedom system (TDFS) appears to be the most complete and versatile model which gives reasonably conservative force limits, and does not require extrapolation of interface force data for similar mounting structures and test articles. However there are some limitations to the complex TDFS model. The model is well adapted for nicely separated modes but issues regarding the closely space modes have not been fully addressed in the literature. Also, the complex TDFS model is based on free boundary conditions for the mounting structure, which appear to be natural for many cases such as spacecraft mounted on a launch vehicle. However this is not necessarily true for some other cases such as an electronic component mounted on a spacecraft antenna, which requires fixed boundary conditions. The main objective of this paper is to give greater insights into the complex TDFS method and propose methodologies to overcome its limitations. It is shown that a simple approach can be used to assure conservative estimate of the force limits in situations regarding closely spaced modes. It is also demonstrated that although the complex TDFS method is not perfectly adapted to fixed boundary conditions of the mounting structure, given certain precautions, it still provides good estimates of the force limits.
Improvement and Evaluation of Metal Thin Films by Very Low Energy Argon Ion Irradiation
Authors: Sasaki Tomonori , Yang Ming , Fujimoto Kinuko
Published: April 2008

A new methodology using very low energy Ar ion irradiation is proposed to improve the mechanical properties of thin metal films deposited by sputtering. In this study, accelerating voltage of Ar ion plasma was set to lower than 100V, and several conditions were applied to irradiations. Consequently, it is found that Young’s modulus and hardness of Aluminum and Nickel thin film increases about 10% by the irradiation compared with a non-irradiated thin film. (111)–oriented integrated intensity of diffraction of Al and Ni thin film was increased by the irradiation. It is considered that crystalline orientation was changed and column spacing of the film be filled by the irradiation. It is shown that the proposed technique is effective to improve the mechanical properties of metal thin films with proper irradiation conditions.
Torque Saturation Analysis in Electromechanical Motor
Authors: Yoo Jae Gu , Tesar Delbert
Published: April 2008

This paper describes the torque and magnetic flux analysis using an advanced dynamic dynamometer test bed for electromechanical motors. Test motor was tested under different levels of continuous loads and high bandwidth complex duty cycle loads in order to provide data to characterize the nonlinear properties of electric motors. The test bed to obtain torque saturation limit data is comprised of a servo motor which serves as a dynamic load emulator, a brake, a clutch, and full sensor array for comprehensive monitoring of test variables, (including magnetic flux density sensor). The magnetic flux test was conducted to discriminate magnetic saturation from torque saturation. Given the permanent magnet motor test system designed for a desired saturation limit, it is possible to predict saturation using a properly defined dynamic duty cycle norm as a function of the operating conditions and the actuator design parameters. In this paper, the temperature effects on the magnetic properties of the permanent magnet material were the principal objectives.
Performance Evaluation of a Miniaturized Machining Center for Precision Manufacturing
Authors: Cox Daniel , Newby Glynn , Park Hyung Wook , Liang Steven Y.
Published: April 2008

The ability to manufacture at the micrometric and even nanometric precision is in strong demand today in view of the increasing need to reduce the size of parts and products in many industrial and commercial sectors. For many of these applications, the technology of mechanical solid tool machining offers promising applicability as it can create truly three-dimensional and one-of-a-kind parts of extremely high resolutions without placing significant limitation on the part materials. For mechanical solid tool machining, the control of three-dimensional motions between machines, tools, and parts to sub-micron level of precision is a perquisite to the realization of manufacturing at such fine scales. One important factor that contributes to the machining process accuracy is the overall size of the machine tool due to the effects of thermal, static, and dynamic stabilities. This paper will assess the technological benefits of miniaturization of machine tools in the context of machine stiffness and accuracy. This paper also presents the design and configuration of a 4-axis miniaturized vertical machining center of positioning accuracy of 4 to 10 nm and a machine volumetric envelop less than 0.03m3, which is several hundred times smaller than traditional machining centers. A series of tests are discussed for performance evaluation of the miniaturized machining center in terms of the achievable finish and part form accuracy with respect to the process parameters and part geometrical complexity in 1-D, 2-D, and 3-D cases.
Tribological Design of Grinding Wheels Using X-Ray Diffraction Techniques
Authors: Jackson M. J.
Published: April 2008

Grinding wheel wear is a significant problem when the wheel has to be continuously dressed in order to maintain high productivity and high quality ground surfaces, especially during the manufacture of camshafts and crankshafts for automotive applications. This paper describes the use of x-rays to specifically engineer bonding systems for conventional abrasive grinding wheels so the wheel wears less during continuous dressing operations. The paper explains how the use of x-rays can be used to develop the next generation of bonding systems that will allow the grinding wheel to be cleaned and dressed with a laser without damaging the structure of the grinding wheel.
Survey of Active Aeroelastic Control for Flutter Suppression
Authors: Anderson Kevin R. , White Kevin , Neal Joe
Published: April 2008

Aeroelastic flutter is the potentially destructive aerodynamic vibration of an elastic body in an air-stream. The interactions of aerodynamic, inertial and structural forces cause coupled torsional and bending modes on the aircraft, which can exceed its structural strength. An aircraft’s wing, tail and control surfaces are at the greatest risk of experiencing flutter. The goal of a flutter suppression system is to clear the flight envelope from flutter. This paper provides an overview regarding the current state-of-the-art hardware, techniques and analytical methods used in implementing Active Aeroelastic Control (AAC) in the design of a flutter suppression system.
Heat Transfer Study of a Novel Low-Crossflow Design for Jet Impingement
Authors: Hebert Ryan , Ekkad Srinath V. , Khanna Vivek , Abreu Mario , Moon Hee-Koo
Published: April 2008

Impingement heat transfer is significantly affected by initial cross-flow or by the presence of cross-flow from upstream spent jets. In this study, a zero cross-flow design is presented. The zero-crossflow design creates spacing between hole arrays to allow for spent flow to be directed away from impinging jets. Three configurations with different impingement holes placements are studied and compared with pure impingement with spent crossflow cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. The zero-cross flow design clearly shows minimal degradation of impingement heat transfer due to crossflow compared to conventional design with lower mass flow rate requirement and lesser number of overall impingement holes due to the reduced cross-flow effect on the impingement region.
Estimation and Control of Heat Transfer in Screw Compressor Rotors
Authors: Stosic N. , Smith I. K. , Kovacevic A.
Published: April 2008

Stage pressure ratios in screw compressors, operating without oil injection, are limited by deformation of the rotors, caused by the temperature rise of the compressed gas. Rotor cooling would reduce this restriction. As a result of identification of the main modes of heat transfer both in the rotors and between the rotors and their surroundings and the relative significance of each, a novel procedure is suggested to cool the rotors by injection of minute quantities of a volatile fluid. By this means the compressed gas should attain higher temperatures without rotor distortion. To confirm these concepts and quantify both the heat transfer rates and the rate of liquid injection required for rotor cooling, both a one dimensional flow study and a more complex 3-D numerical analysis were performed, the latter with the aid of a CFD code. The results indicated that the rotors could be maintained at a far lower temperature than that of the discharged gas by flash evaporative cooling, as a result of injecting a fractional percentage by mass of a volatile fluid. This was confirmed by experiment. This technique may be used to operate dry compressors at substantially higher pressure ratios than are currently possible in such machines. It is also shown that only minor design changes are needed to implement it.
Obstacle Avoidance for Groups of Mobile Robots Using Potential Field Technique
Authors: Fahimi F. , Nataraj C. , Ashrafiuon H.
Published: April 2008

An efficient real time path planning method for groups of mobile robots in dynamic environments is introduced. Harmonic potential functions are utilized along with the panel method known in fluid mechanics. First, a complement to the traditional panel method is introduced to generate a more effective harmonic potential field for obstacle avoidance in dynamically changing environments. Second, a group of mobile robots working in an environment containing stationary and moving obstacles is considered. Each robot is assigned to move from its current position to a goal position. The group is not forced to maintain a formation during the motion. Every robot considers the other robots of the group as moving obstacles and hence the physical dimensions of the robots are also taken into account. The path of each robot is planned based on the changing position of the other robots and the position of stationary and moving obstacles. Finally, the effectiveness of the scheme is shown by modeling groups of an arbitrary number of mobile robots and the theory is validated by several computer simulations and hardware experiments.
Reinventing Engineering Statics to Address the Conceptual Difficulties of Students
Authors: Steif Paul S. , Dolla´r Anna
Published: April 2008

The goal of Statics instruction should be its application to gaining insight into, and to designing, engineering systems. The typical textbook experience, relying strongly on mathematical manipulations, is not adequate to preparing students to model mechanical systems. Experienced users of mechanics rely on an intuitive, even visceral, sense for the forces which are present in mechanical systems, and how they combine to maintain the system in equilibrium (or produce its motion). With the observation that students do not readily perceive forces between inanimate objects, we have reorganized Statics instruction to focus initially on situations in which they can experience forces directly: forces exerted by hand or that are evident from motion or deformation. Within this overall philosophy, we developed learning modules that address discrete concepts with which students traditionally have difficulty. Learning modules include simple objects to manipulate, PowerPoint presentations, and multiple-choice questions relevant to the concepts that the modules convey. In this paper we identify a series of important concepts in Statics, and we offer several excerpts from new or improved Learning Modules, focusing on how the Learning Module seeks to address students’ conceptual difficulties.
The Evolution of Games of Innovation in Regulated Complex Industries: The Case of Aviation Training
Authors: Kamel Michael , Miller Roger
Published: April 2008

The study of industrial games of innovation is often associated with dominant theories representing various generic forms of organizational design and dynamics. The dominant theories in this area were traditionally Schumpeter’s destructive innovation, Porter’s five-force competitive analysis and Nalebuff’s value net. Other frameworks for analyzing industrial behavior include game theory and its derivative innovation games theory. For regulated high-technology industries, theoretical frameworks that do not account for interfirm coordination are often insufficient to understand or predict the industry behavior. Innovation in the aviation simulation and training industry will be presented in this paper as typical of the regulated high-technology industries. The aviation simulation and training industry emerged at the turn of the twentieth century and it was mostly demand-driven at its onset. The increase in the volume and importance of aviation resulted in government regulation of the industry in the late 1960’s. This has radically changed the industry’s game of innovation into a regulation-based coordination game. Literature described the regulation-centered innovation coordination as “an internally-coherent system of innovation.” The new game had the regulatory frameworks at the core of the innovation process as they defined the market’s acceptance and value capturing from innovative technologies. The evolution of these regulatory frameworks was almost entirely reactive to accidents and catastrophic failures that highlighted existing deficiencies in training methodologies or technologies. This ex-ante regulator-driven system of innovation exhibited recent evolutionary changes towards being a pedagogy-centered service-based system of innovation. The reason behind this transformation was a combination of endogenous and exogenous forces. Technological opportunities, economic pressures and strategic transformation by industry leaders were the three main categories of these forces. The resulting mode of innovation coordination in the industry was a service-oriented pedagogical platform, lead by supplier-user partnerships and monitored by regulation authorities. Compliance to equipment regulatory guidelines is not the principal means of value creation anymore. Rather, the pedagogic value of the training curriculum, encompassing the training devices, is the main source of value creation. A new stable equilibrium of innovation coordination is being reached by the industry, driven by its downstream-most service provision component.
Static and Dynamic Loading Behaviour of Auxetic Thermoplastic Foams
Authors: Pastorino Paolo , Scarpa Fabrizio
Published: April 2008

The paper describes the manufacturing and tensile testing of auxetic (negative Poisson’s ratio) thermoplastic polyurethane foams. The foams are produced from conventional flexible polyurethane basis following a manufacturing route developed in previous works. The Poisson’s ratio behavior over tensile strain has been analyzed using an Image Data processing technique based on Edge Detection from digital images recorded during quasi-static tensile test. The samples have been subjected to tensile and compressive tests at quasi-static and constant strain-rate values (up to 12 s−1). Analogous tests have been performed over iso-volumetric foams samples, i.e., foams subjected to the same volumetric compression of the auxetic ones, without exhibiting a negative Poisson’s ratio behavior. A model describing the compressive stress-strain behavior of the auxetic foams has been developed considering the stress-strain performance of single unit cell and making use of statistical distributions of relative densities and buckling loads on auxetic foam cells during loading.
Amplitude-Limiting Feedback Control of Combustion Instability With a High-Momentum Air Jet
Authors: Uhm Jong Ho , Acharya Sumanta
Published: April 2008

A new strategy that integrates low-frequency modulation of a high-momentum air-jet with amplitude feedback is presented for control of combustion oscillations in a swirl-stabilized spray combustor. The oscillations in the combustor of interest are dominated by an acoustic mode (235 Hz) with a low frequency (13 Hz) bulk-mode (of the upstream cavity) superimposed. An effective strategy for control is shown to be achieved through the use of a concept which utilizes low bandwidth modulation of a high-momentum air-jet that penetrates into the regions of positive Rayleigh index. It is shown that with a low frequency modulation (5 Hz) of the high momentum air-jet, the pressure oscillations can be reduced significantly (by a factor of nearly 6). Further improvement in control is achieved with an amplitude-limiting feedback strategy, in which, the valve opening and closing of the control air-jet is driven by the pressure amplitude relative to a specified threshold. The goal of the controller is to maintain pressure oscillations below the pre-set threshold level. With this strategy, the valve frequency and duty cycle are automatically adjusted based on the amplitude of the pressure signal. It is observed that modulation frequencies are typically in the range of 5–30 Hz (although higher frequencies, as high as 130 Hz, are needed occasionally). Duty cycles less than 50% are required for effective control. The amplitude-limiting feedback controller is shown to combine the benefits of low-bandwidth actuation, low-duty cycles, and greater reductions in pressure oscillations.
Effectiveness of Utilizing Computer Assisted Instruction in Teaching CAD to Engineering Students
Authors: Attia Farouk , Elsamahy Ibrahim
Published: April 2008

This paper presents the results of an experimental study to investigate and evaluate the effectiveness of utilizing computer-assisted instruction (CAI) as a stand-alone educational tool to teach computer-aided drafting (CAD) in engineering and technology programs. While the literature is rich with research in the field of evaluating CAI as a supplementary educational tool [11], a very limited number of publications dealt with evaluating CAI as a stand-alone system [7, 16, 9]. Also, none of the published studies focused on engineering or engineering technology education utilizing CAD systems. In this way, the present study serves as benchmark in devising a system to evaluate the effectiveness of CAI modules as a stand-alone instructional tool in engineering and technology education. In the present study, the students’ cognitive performance was measured in an entry-level CAD course. The participating students were divided into two groups: 1) the Primary Experimental group, which received only the CAI module as their sole source of instruction. This group was strictly involved in self-learning, self-paced instruction with minimum interaction with the instructors or lab assistants during the length of the study. 2) The Control group, which received only conventional instruction (lectures, handouts, textbook, and lab workbook) with all the necessary support from the instructors and lab assistants. A pilot study was conducted to pre-test the measuring instrument and the grading procedures as well as the methodology of assigning the students into groups. It was concluded one semester prior to the start of the main experiment. The main study was conducted over a period of three regular semesters with a new set of two groups of students selected for each semester. At the end of each experiment, the students were given a test (the measuring instrument) that was identical for both groups. The test results were tabulated and analyzed statistically. Statistical analysis of the data collected indicated that the group of students who received conventional instruction performed better than those receiving only computer-assisted instruction (CAI). Since several factors could have contributed to these findings, a major significance of the current study is that it demonstrates the necessity to conduct similar studies at different institutions in order to evaluate the effectiveness of CAI technology as it becomes more prevalent in engineering education programs [13].
Fabrication of Meso- and Micro-Structured Devices by Direct-Write Deposition and Laser Processing of Dry Fine Powders
Authors: Kumar Pranav , Das Suman
Published: April 2008

We present a multi-material rapid prototyping technique for producing 2D and layered 3D meso- and micro-structured multi-functional devices with spatially varying heterogeneous material compositions. This technique involves direct-write deposition of multiple, patterned powder materials followed by laser sintering. The direct-write deposition system features miniature hopper-nozzles for depositing dry powdered materials by gravity or by high frequency vibration-assisted flow on to a movable substrate. Deposition of 10–125μm powder particles via 100μm-2mm hopper-nozzles orifices has yielded a 100μm minimum attainable feature size for device footprints ranging from sub-milimeter to a few centimeters. The feasibility of this direct-write concept was proved by patterning single and multiple materials onto substrates to demonstrate various prototype devices envisaged by this technique. These include micro-battery, interdigitated capacitor, fractal antenna, Swiss-roll microcombustor, and functionally graded polymeric bioimplants.
Control Valve Design Impact on Piping Vibration
Authors: McGhee James , Newlands Doug , Farquhar Stuart , Miller Herbert L.
Published: April 2008

Vibration of the recycle piping system on the Main Oil Line (MOL) Export Pumps from a platform in the North Sea raised concern about pipe breakage due to fatigue. Failures had already occurred in associated small bore piping and the instrument air supply lines and control accessories on the recycle flow control valves. Concern also existed due to the vibration of non-flowing pipe work and systems such as the deck structure, cable trays and other instrumentation, which included fire and gas detection systems. Many changes involving bracing of small bore attachments, stiffening of supports, adding supports and stiffing the deck structure were implemented without resolving the problem. The vibration was finally solved by adding enough pressure stages to assure the valve trim exit velcoities and energy levels were reduced to levels demonstrated historically as needed in severe service applications. This vibration energy reduction was more than 16 times. This was achieved by reducing the valve trim exit velocity from peaks of 74 m/s to 12 m/s (240 ft/s to 40 ft/s).
Anisotropic Elastoplastic Behavior of SiCp/Al Composite Sheets
Authors: Skolnik D. A. , Liu H. T. , Sun L. Z. , Wu H. C.
Published: April 2008

Experimental research was performed to study the anisotropic elastoplastic responses of SiCp/Al composite sheets. To investigate the effects of the composite processing, two sets of specimens cut from the heat-treated and as-rolled composite sheets are tested using a universal material-testing machine. The dependence of the strength, plastic flow, and strain ratios on the rolling angles are discussed in detail. To model the phenomena observed in the experiments, a micromechanics based damage framework is developed. The interfacial debonding and the rolling angle’s effects are integrated into this model. Good consistence between the experimental results and the analytical predications shows the validity of the theoretical model.
Efficient Methods for Numerical Modelling of Laminar Friction in Fluid Lines
Authors: Johnston D. Nigel
Published: April 2008

An improved method for simulating frequency-dependent friction in laminar pipe flow using the Method of Characteristics (MOC) is proposed. It has a higher computational efficiency than previous methods whilst retaining a high accuracy. By lumping the frequency-dependent friction at the ends of the pipeline the computational efficiency can be improved further, at the expense of a slight reduction in accuracy. The technique is also applied to the Transmission Line Method (TLM) and found to give a significant improvement in accuracy over previous methods, whilst retaining a very high computational efficiency.
Investigation of Electrode Degradation in Alkaline Fuel Cells: A Research Proposal
Authors: Rivas J. M. , Martinez-Frias J. , Aceves Salvador M.
Published: April 2008

Recent efforts in the development of fuel cell technology have concentrated on Proton Exchange Membrane, Solid Oxide, Molten Carbonate, and more recently, Direct Methanol fuel cells. Alkaline fuel cells, on the other hand, have received considerably less attention despite their successful use in the early years of the NASA Space Program. Alkaline fuel cells, however, still offer considerable potential as a viable energy conversion alternative, especially if the cell is incorporated into a regenerative system where the required reaction gases are produced. In this work, a review of the current status of development of alkaline fuel cells is undertaken with the objective of identifying areas for advancement of alkaline fuel cell technology. Specific areas of research have been identified and are described. These areas include detailed studies characterizing the evolution of the degradation of electrodes in alkaline fuel cells.
Is There a Best Fixed-Geometry Valve for Micropumps?
Authors: Gamboa Adrian R. , Forster Fred K.
Published: April 2008

Two frequently used geometries for fixed-valve micropumps are the nozzle-diffuser and Tesla-type valve. However, little work has been done to investigate the relative merits of optimal shapes for each type of valve. In this study 2D steady-state computational fluid dynamics coupled with a formal optimization procedure and experimental evaluation were performed to address this problem. Non-dimensionalization of the problem allowed a comparison of the two valve types independent of physical size, i.e. shape alone was studied. Optimal shapes were found based on maximizing calculated diodicity as a function of Reynolds number in conjunction with a weighting function used to control forward pressure drop. The optimal shape for each valve was then compared numerically and experimentally to reference valves similar to those reported in the literature. The optimal shape for each valve type was found to be significantly different from the reference shape and exhibited significantly improved performance. Both valve types achieved a maximum diodicity of approximately two in the range of Reynolds number 0 ≤ Re ≤ 2000. The optimal Tesla-type valve was characterized by a large return loop and shallow return loop angle. The optimal nozzle-diffuser was characterized by a very long diffuser section that prevented flow separation in the forward flow direction along with increased wall shear stress in the reverse flow direction. The diodicity vs Reynolds number curve for the Tesla-type valve monotonically increased, while the nozzle-diffuser exhibited a local maximum in the mid-Reynolds number range. These characteristics may play an important role when valve size is determined to maximize resonant behavior of a micropump. Thus they influence numerous pump design criteria such as target flow rate-pressure characteristics and overall pump size.
Coalescence Criterion of Part-Through Wall Cracks in Steam Generator Tubes of Nuclear Power Plants
Authors: Abou-Hanna Jeries , McGreevy Timothy , Majumdar Saurin , Trivedi Amit J. , Al-Hayek Ashraf
Published: April 2008

In scheduling inspection and repair of nuclear power plants, it is important to predict failure pressure of cracked steam generator tubes. Nondestructive evaluation (NDE) of cracks often reveals two neighboring cracks. If two neighboring part-through cracks interact, the tube pressure, under which the ligament between the two cracks fails, could be much different than the critical burst pressure of an individual equivalent part-through crack. The ability to accurately predict the ligament failure pressure, called “coalescence pressure,” is important. The coalescence criterion, established earlier for 100% through cracks using nonlinear finite element analyses [1–3], was extended to two part-through-wall axial collinear and offset cracks cases. The ligament failure is caused by local instability of the radial and axial ligaments. As a result of this local instability, the thickness of both radial and axial ligaments decreases abruptly at a certain tube pressure. Good correlation of finite element analysis with experiments (at Argonne National Laboratory’s Energy Technology Division) was obtained. Correlation revealed that nonlinear FEM analyses are capable of predicting the coalescence pressure accurately for part-through-wall cracks. This failure criterion and FEA work have been extended to axial cracks of varying ligament width, crack length, and cases where cracks are offset by axial or circumferential ligaments. The study revealed that rupture of the radial ligament occurs at a pressure equal to the coalescence pressure in the case of axial ligament with collinear cracks. However, rupture pressure of the radial ligament is different from coalescence pressure in the case of circumferential ligament, and it depends on the length of the ligament relative to crack dimension.
A Numerical Study Concerning Indirect Ice Storage Tanks Performance
Authors: Stampa Cleyton S. , Nieckele Angela O.
Published: April 2008

A numerical investigation regarding the charging process behavior occurring in a typical indirect ice storage tank is presented. It consists of analyzing the heat transfer and removal of energy, applicable to storage systems, which are chiller-based. In this sense the secondary coolant circulates through a heat exchanger that is submerged in a tank of water and it is used to freeze (charge) the phase-change material (water), which never leaves the storage tank. The thermal exchange process is investigated in critical regions formed between the heat exchanger wall and the tank wall. The present study simulates such regions through a channel formed by parallel flat plates, one of which is the heat exchanger, and investigates the heat transfer effects considering it in two different positions. In the first one the channel is in the vertical position, while for the second, it is horizontally positioned. Our task is to provide helpful qualitative results for the heat transfer performance of ice storage tanks. The results are analyzed through streamlines and isotherms, for specific instants of time. Further, the heat transfer effectiveness, average heat flux and solid formed at one of the two plates of the channel, are compared for the vertical and horizontal positions of the channel, as well as different distances from the heat exchanger and tank wall.
Algebraically Explicit Analytical Solutions of Unsteady Conduction With Variable Thermal Properties in Spheroidal Coordinates
Authors: Cai Ruixian , Zhang Na
Published: April 2008

The analytical solutions of unsteady heat conduction with variable thermal properties (thermal conductivity, density and specific heat are functions of temperature or coordinates) are meaningful in theory. In addition, they are very useful to the computational heat conduction to check the numerical solutions and to develop numerical schemes, grid generation methods and so forth. Such solutions in rectangular coordinates have been derived by the authors; some other solutions for unsteady point symmetrical heat conduction in spherical coordinates are given in this paper to promote the heat conduction theory and to develop the relative computational heat conduction.
A Novel Ammonia-Water Cycle for Power and Refrigeration Cogeneration
Authors: Zhang Na , Cai Ruixian , Lior Noam
Published: April 2008

Cogeneration can improve the energy utilization efficiency significantly. In this paper, a new ammonia-water system is proposed for the cogeneration of refrigeration and power. The plant operates in a parallel combined cycle mode with an ammonia-water Rankine cycle and an ammonia refrigeration cycle, interconnected by absorption, separation and heat transfer processes. The performance was evaluated by both energy and exergy efficiencies. The influences of the key parameters, which include the rectifier operation pressure, reflux ratio and reboiler temperature, the basic working solution concentration, the cooling water temperature and the Rankine cycle turbine inlet parameters on the cycle performance, were investigated. It is found that the cycle has a good thermal performance, with energy and exergy efficiencies of 25% and 50.9%, respectively, for the base-case studied (having a maximum cycle temperature of 450°C). Comparison with the conventional separate generation of power and refrigeration having the same outputs, shows that the energy consumption of the cogeneration cycle is lower by 21.6%.
Mechanical Engineering Education: Not Just About the Math
Authors: Foroudastan Saeed D. , Saxby Dyani
Published: April 2008

It is of utmost importance that universities seek out creative ways to enhance the written and oral communication skills of their engineering students. Too many engineering students graduate and enter today’s competitive job market without sufficient communication skills that will ultimately give them an edge in their profession. It takes hard work and perseverance to obtain a four-year engineering degree, yet many talented students may be overlooked due to inadequate communication skills. Although a student may be more than qualified for an engineering position, a lack of written and oral communication skills could have a negative impact on his or her perceived level of skill. Employers today are searching for well-rounded individuals who are capable of performing multiple job tasks. They demand engineers who are not only technically astute, but who can also conduct research and effectively communicate their ideas to others. This paper examines the importance of written and oral communication skills in engineering professions. Additionally, it investigates various methods of teaching written and oral communication skills to many engineering students, including mechanical engineering, in higher education. It also describes the methods employed by the authors to enhance the communication skills of engineering technology students at Middle Tennessee State University (MTSU). Top priority should be given to see that students are able to live up to the highest standards both academically and professionally. It is time that universities empowered their students with the additional skills necessary to survive and flourish in today’s competitive and demanding job market.
Sites of Kinetically Critical Femoral Head Roughening for Third Body Acceleration of Total Hip Implant Wear
Authors: Lundberg Hannah J. , Stewart Kristofer J. , Brown Thomas D.
Published: April 2008

Polyethylene debris shed during the use of total hip implants can result in debris-induced aseptic loosening. This aseptic loosening is the leading cause of implant failure. Total hip implant wear is highly variable and can be accelerated by third body ingress and subsequent roughening of the metal femoral head counterface. Up to 40% of clinical wear rate variance may be attributable to third body effects [1]. It is hypothesized that the location of counterface roughening will have dramatic effects on the induced implant wear. Using a previously validated sliding-distance-coupled contact finite element (FE) model of total hip implant wear [2], we identified regions of the femoral head surface that, when roughened, result in maximal wear. By implication, these are the sites most important to protect from third body access.