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2004

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Articles 1 - 30 of 375

Full-Text Articles in Mechanical Engineering

Computational Studies Of Viscoelastic Multiphase Flows, Shriram B. Pillapakkam Dec 2004

Computational Studies Of Viscoelastic Multiphase Flows, Shriram B. Pillapakkam

Dissertations

A finite element code based on the level set method is developed for performing two and three dimensional direct numerical simulations (DNS) of viscoelastic two-phase flow problems. The Oldroyd-B constitutive equation is used to model the viscoelastic liquid. The code is used to study transient and steady state shapes of Newtonian and viscoelastic drops in simple shear and buoyancy driven flows. The roles of the governing dimensionless parameters: Capillary number (Ca), Deborah Number (De) and the polymer concentration parameter c, in determining deformation of drops and bubbles, are also analyzed.

The numerical code permits us to vary Ca, De and ...


Experimental Technique For Studying High-Temperature Phase Equilibria In Reactive Molten Metal Based Systems, Alexandre Ermoline Dec 2004

Experimental Technique For Studying High-Temperature Phase Equilibria In Reactive Molten Metal Based Systems, Alexandre Ermoline

Dissertations

The general objective of this work is to develop an experimental technique for studying the high-temperature phase compositions and phase equilibria in molten metal-based binary and ternary systems, such as Zr-O-N, B-N-O, Al-O, and others. A specific material system of Zr-O-N was selected for studying and testing this technique.

The information about the high-temperature phase equilibria in reactive metal-based systems is scarce and their studying is difficult because of chemical reactions occurring between samples and essentially any container materials, and causing contamination of the system.

Containerless microgravity experiments for studying equilibria in molten metal-gas systems were designed to be conducted ...


Investigation Of Static And Dynamic Enhancement Of Laminar Natural Convection Cooling Of Electronics, Laurie Ann Florio Dec 2004

Investigation Of Static And Dynamic Enhancement Of Laminar Natural Convection Cooling Of Electronics, Laurie Ann Florio

Dissertations

With the proliferation of consumer electronics devices and the increasingly demanding thermal control requirements for such devices, more effective and efficient means of cooling electronics are needed. The feasibility of three alternative approaches to enhancing pure natural convection cooling of electronics is investigated in the current research. The three static or dynamic methods investigated are alternate cross-flow passages, the strategic placement of transversely oscillating plates near the heat sources and a combined method using both the cross-flow passages and the strategically placed oscillating plates. These cooling methods are intended to operate in the regime for which natural convection cooling is ...


High Temperature Heat Exchanger Project: Quarterly Progress Report October 1, 2004 Through December 31, 2004, Anthony Hechanova Dec 2004

High Temperature Heat Exchanger Project: Quarterly Progress Report October 1, 2004 Through December 31, 2004, Anthony Hechanova

Publications (NSTD)

UNLV hosted an NHI Systems Interface Meeting on Dec. 16 and a UNLVRF HTHX Kickoff Meeting on Dec. 17. The purpose of the meetings was to coordinate the FY05 research and development effort of the UNLV Research Foundation portion of the Nuclear Hydrogen Initiative among the DOE, national program technical directors and the UNLVRF collaborators. Collaborators also had the opportunity to discuss their research program plan and update their progress. It was decided that these type of collaboration meetings were very useful and they will be held quarterly at the various collaborator sites. The next meeting will be in March ...


Dec 2004, Tractor Museum Dec 2004

Dec 2004, Tractor Museum

Museum Planning and Development Documents

Introductions Treasurer's Report Curator's Report


New Product Launch Decisions Under Competition And Uncertainty: A Real Options And Game-Theoretic Approach To New Product Development, James O. Ostler Dec 2004

New Product Launch Decisions Under Competition And Uncertainty: A Real Options And Game-Theoretic Approach To New Product Development, James O. Ostler

Theses and Dissertations

New product development is central to many firms' future success. Not only as a means to continue to maintain their piece of the market, but product development can also be a strategic means for a company to diversify, and/or alter focus to adapt to changing market conditions.

Most of the research in new product development has been on how to do it cheaper and faster than the next guy. However, early commercialization does not guarantee a position of strength in the market. Failures of EMI in CT scanners and Xerox in personal computers illustrate that being first to market ...


Dynamic Stability And Handling Qualities Of Small Unmanned-Aerial-Vehicles Unmanned-Aerial-Vehicles, Tyler Michael Foster Dec 2004

Dynamic Stability And Handling Qualities Of Small Unmanned-Aerial-Vehicles Unmanned-Aerial-Vehicles, Tyler Michael Foster

Theses and Dissertations

General aircraft dynamic stability theory was used to predict the natural frequencies, damping ratios and time constants of the dynamic modes for three specific small UAVs with wingspans on the scale from 0.6 meters to 1.2 meters. Using USAF DatCom methods, a spreadsheet program for predicting the dynamic stability and handling qualities of small UAVs was created for use in the design stage of new small UAV concept development. This program was verified by inputting data for a Cessna-182, and by then comparing the program output with that of a similar program developed by DAR Corporation. Predictions with ...


A Finite Element Simulation Of Temperature And Material Flow In Fricton Stir Welding, Mark J. Lasley Dec 2004

A Finite Element Simulation Of Temperature And Material Flow In Fricton Stir Welding, Mark J. Lasley

Theses and Dissertations

The purpose of this research was to use the Transvalor S.A. product, Forge3, to develop a finite element simulation of the friction stir welding process that improves the predictability of temperature evolution and material flow within the plunge portion of the process. Previous modeling created more heating within the billet than experimental results, probably due to the simplification of the simulation with adiabatic boundary conditions. More realistic tooling temperatures were included in this model as these affect heat evolution which is a determining factor in microcrystalline growth. These results were validated by experimental efforts using a billet and tooling ...


A Method For Winding Advanced Composites Of Unconventional Shapes Using Continuous And Aligned Fibers, Abraham K. Allen Dec 2004

A Method For Winding Advanced Composites Of Unconventional Shapes Using Continuous And Aligned Fibers, Abraham K. Allen

Theses and Dissertations

Advanced composites are extremely strong, rigid, and light, even when compared with advanced metals. Advanced composites are replacing high-tech metals as the material of choice for aerospace engineering. However, the processes used to manufacture advanced composites generally lose some of the properties of the materials by their process limitations.

One process that keeps the theoretically awesome qualities of the composite materials in tact is filament winding. Filament wound parts are used as rocket shells, bicycle frame tubes, drive shafts, pressure vessels, etc. Filament winding is an automated process and makes reliable parts to close tolerances. If a straight tube were ...


Stam: A System Of Tracking And Mapping In Real Environments, Ying Zhang, Lee Ackerson, David Duff, Craig Eldershaw, Mark Yim Dec 2004

Stam: A System Of Tracking And Mapping In Real Environments, Ying Zhang, Lee Ackerson, David Duff, Craig Eldershaw, Mark Yim

Departmental Papers (MEAM)

We have implemented a system of tracking mobile robots and mapping an unstructured environment, using up to 25 wireless sensor nodes in an indoor setting. These sensor nodes form an ad hoc network of beacons, self-localize with respect to three anchor nodes, and then track the locations of mobile robots in the field. The system described here was motivated by search and rescue applications, and has been demonstrated in real physical environments.


Yield Behavior Of Commercial Al-Si Alloys In The Semisolid State, Q. Y. Pan, Diran Apelian, A. N. Alexandrou Dec 2004

Yield Behavior Of Commercial Al-Si Alloys In The Semisolid State, Q. Y. Pan, Diran Apelian, A. N. Alexandrou

Mechanical Engineering Faculty Publications

Systematic experimental work and modeling efforts have been conducted to characterize the yield behavior of commercial aluminum alloys in the semisolid state. In this study, extensive compression experiments were performed to measure the yield stress of semisolid aluminum slurries at high solid fractions (0.5 to 1.0), and a cone penetration method was employed to measure yield stress at low solid fractions (<0.5). A functional relationship between yield stress and temperature/solid fraction has been established for these alloys. The effect of the processing route on the resultant yield stress of the material in the semisolid state was studied by evaluating commercial A356 billets manufactured via magnetohydrodynamic stirring, grain refining, and UBE'S new rheocasting (NRC) processes, respectively. Detailed microstructure observations and image analyses reveal that the difference in yield-stress values among the alloys evaluated is intricately related to the semisolid structure. At a given solid fraction, the yield stress of semisolid slurries depends on microstructural indices (i.e., entrapped-liquid content, shape factor of the alpha phase, and the alpha particle size). In addition, numerical simulation results indicate that the finite yield stress of semisolid metals plays a significant role in determining the flow pattern during die filling. Depending on processing conditions, five distinct filling patterns (shell, disk, mound, bubble, and transition) have been identified and confirmed through experimental observations. Recent simulations demonstrate that the finite yield stress is also responsible for flow instabilities encountered in commercial forming operations, such as "toothpaste behavior." Specifically, most flow instabilities can be avoided by properly controlling processing parameters and the initial semisolid microstructure. A stability map that provides a control guide for semisolid processing has been developed and is presented.


A Growth Pathway For Highly Ordered Quantum Dot Arrays, Jianyu Liang, Hailin Luo, Rod Beresford, Jimmy Xu Dec 2004

A Growth Pathway For Highly Ordered Quantum Dot Arrays, Jianyu Liang, Hailin Luo, Rod Beresford, Jimmy Xu

Mechanical Engineering Faculty Publications

To realize the desired zero-dimensional behavior of a quantum dot ensemble, the ability to fabricate quantum dots with a high packing density and a high degree of size, shape, and spacing uniformity is crucial. Here we report highly ordered InAs nanodot arrays grown by molecular-beam epitaxy on nonlithographically nanopatterned GaAs. Approximately 20 billion dots are grown in a 1 cm2 area with the smallest size dispersion ever reported and forming a lateral superlattice in hexagonal dense packing form. These techniques presage a pathway to controlled growth of periodic quantum dot superstructures, which offer macroscopic spatial coherence in the interaction of ...


Thermodynamic Analysis Of Separation Systems, Yasar Demirel Dec 2004

Thermodynamic Analysis Of Separation Systems, Yasar Demirel

Papers in Thermal Mechanics

Separation systems mainly involve interfacial mass and heat transfer as well as mixing. Distillation is a major separation system by means of heat supplied from a higher temperature level at the reboiler and rejected in the condenser at a lower temperature level. Therefore, it resembles a heat engine producing a separation work with a rather low efficiency. Lost work (energy) in separation systems is due to irreversible processes of heat, mass transfer, and mixing, and is directly related to entropy production according to the Gouy-Stodola principle. In many separation systems of absorption, desorption, extraction, and membrane separation, the major irreversibility ...


Effects Of Pressure And Equivalence Ratio On Minimum Ignition Energies Of Methane-Air Mixtures And Effect Of Pressure On Breakdown Threshold Energies Of Methane And Air, Sameer Vidyadhar Bondre Dec 2004

Effects Of Pressure And Equivalence Ratio On Minimum Ignition Energies Of Methane-Air Mixtures And Effect Of Pressure On Breakdown Threshold Energies Of Methane And Air, Sameer Vidyadhar Bondre

Masters Theses

An experimental investigation is conducted to determine the effect of pressure on breakdown threshold energies of methane and air. In addition the effect of pressure and equivalence ratios on minimum ignition energies of methane-air mixtures are also investigated. The pressures for the breakdown threshold energy experiments are varied from 0.02 to 1.17 MPa, and pressures and equivalence ratios for minimum ignition energy experiments are varied from 0.1 to 1.04 MPa and 0.6 to 1.2, respectively. The gas breakdown and the ignition of the methane-air mixture is achieved using a laser-induced spark from a 5 ...


Design And Parameter Identification Of A Discrete Variable Transmission System, Kelley Parker Brown Dec 2004

Design And Parameter Identification Of A Discrete Variable Transmission System, Kelley Parker Brown

Masters Theses

Complex and expensive electro-hydraulic systems have shouldered the workload for remote cleanup operations in radiological and toxicological areas in the past; the payload, reach and speed requirements of most applications have demanded their use. Electromechanically actuated systems (EAS) however offer an alternative that in comparison is much more reliable and maintainable. The problems faced in implementing the EAS are in high payload operations where the hydraulic systems hold a clear power density advantage. For the EAS to compete in the area of torque, very large DC motors have been implemented which make them obsolete in restricted work space areas and ...


Cure Behavior Study And Elastic Modulus Characterization Of Resin System Of A Quasi Poloidal Stellarator Modular Coil, Hariharanath Kavuri Dec 2004

Cure Behavior Study And Elastic Modulus Characterization Of Resin System Of A Quasi Poloidal Stellarator Modular Coil, Hariharanath Kavuri

Masters Theses

Composites materials are increasingly becoming choice materials because of their tremendous strength-to-weight properties and impressive design flexibility. A more recent application of composites is in nuclear fusion reactors. One such reactor is the Quasi-Poloidal Stellarator (QPS) being developed by Oak Ridge National laboratory. QPS, with a non-axisymmetric, near-poloidally symmetric magnetic configuration, has stranded copper/epoxy composite coils, used for magnetic confinement of plasma. CTD- 404 and CTD-101K are the resins under consideration for the modular coils with copper fiber as reinforcement. Structural integrity of the modular coils over wide range of temperatures, including liquid nitrogen temperature, is of vital importance ...


Lean Nox Trap Catalysis For Lean Burn Natural Gas Engines, Aaron Michael Williams Dec 2004

Lean Nox Trap Catalysis For Lean Burn Natural Gas Engines, Aaron Michael Williams

Masters Theses

As the nation’s demand for energy grows along with concern for the environment, there is a pressing need for cleaner, more efficient forms of energy. The internal combustion engine is well established as one of the most reliable forms of power production. They are commercially available in power ranges from 0.5 kW to 6.5 MW, which make them suitable for a wide range of distributed power applications from small scale residential to large scale industrial. In addition, alternative fuels with domestic abundance, such as natural gas, can play a key role in weaning our nations dependence on ...


Stress Corrosion Cracking And Hydrogen Embrittlement Of Martensitic Alloy Ep-823, Mohammad K. Hossain Dec 2004

Stress Corrosion Cracking And Hydrogen Embrittlement Of Martensitic Alloy Ep-823, Mohammad K. Hossain

UNLV Theses, Dissertations, Professional Papers, and Capstones

This investigation is focused on the evaluation of stress corrosion cracking (SCC), localized corrosion, and hydrogen embrittlement (HE) susceptibility of martensitic Alloy EP-823 in neutral and acidic solutions at ambient and elevated temperatures. While no failures were observed in smooth specimens in the neutral solution, failures were noticed in the 90°C acidic solution at constant-load (CL) leading to a threshold stress (O'th) of 102 ksi. The presence of a notch reduced the O'th value to 91 ksi in a similar environment. The ductility (%El and %RA), time-to-failure (TTF), and true failure stress (O'r) were gradually reduced ...


Stress Corrosion Cracking Resistance Of Martensitic Stainless Steels For Transmutation Applications, Phani P. Gudipati Dec 2004

Stress Corrosion Cracking Resistance Of Martensitic Stainless Steels For Transmutation Applications, Phani P. Gudipati

UNLV Theses, Dissertations, Professional Papers, and Capstones

The susceptibility of Alloy EP-823 to stress corrosion cracking has been evaluated using smooth and notched cylindrical specimens in neutral and acidic solutions at ambient and elevated temperatures using constant load and slow strain rate testing (SSR) techniques. C-ring and U-bend specimens have also been tested in the acidic solution. The effect of hydrogen on the cracking susceptibility has been evaluated under controlled cathodic potential. While no failures were observed with smooth specimens at constant load, the notched specimens showed failure. The SSR test results indicate that the true failure stress (o'f), time to failure and ductility parameters were ...


Cfd Analysis Of 3-D Thermalhydraulics Flow Effects On Wall Concentration Gradient Profiles For Lbe Loop Fittings, Narain Armbya Dec 2004

Cfd Analysis Of 3-D Thermalhydraulics Flow Effects On Wall Concentration Gradient Profiles For Lbe Loop Fittings, Narain Armbya

UNLV Theses, Dissertations, Professional Papers, and Capstones

The objective of the thesis is to study the effects of thermalhydraulics flows on the wall concentration gradient profiles in LBE loop fittings. To that end detailed models of the fittings have been constructed to study these effects. These fittings include sudden expansion, sudden contraction, t-joint and elbow. The typical flow rates chosen for these simulations are typical of design criteria chosen for the loop with Reynolds numbers expected around 200,000 and the usual axial temperature profiles which are being characterized in the DELTA loop at LANL. STAR-CD is the simulation package used to make these predictions, which include ...


Retrieval Of Nano-Size Particles From A Solid Substrate, Krishna Prasad Podila Dec 2004

Retrieval Of Nano-Size Particles From A Solid Substrate, Krishna Prasad Podila

Masters Theses

The retrieval of nano-size particles from suspects and crime scenes can significantly enhance surveillance and crime investigation. The Thesis deals with extensive study of free surface energy coupled with Hertzian contact energy under different conditions between a nano-sized particle and a substrate and the various methods of dislodging the particle. Using the Johnson-Kendall-Roberts (JKR) theory, a physical spring-mass-damper model is defined. Mathematical equations are formulated and solved with non-linear equations simulating the real world situation. Using Newmark’s β method, the system is solved for response of free and forced vibrations taking moisture to be responsible for damping. Key assumptions ...


Prediction Of Interlaminar Shear Strength Of A Thermally Aged Carbon/Epoxy Composite Material By Fourier Transform Infrared Photoacoustic Spectroscopy, Jeffrey J. Sweterlitsch, Roger W. Jones, David K. Hsu, John F. Mcclelland Dec 2004

Prediction Of Interlaminar Shear Strength Of A Thermally Aged Carbon/Epoxy Composite Material By Fourier Transform Infrared Photoacoustic Spectroscopy, Jeffrey J. Sweterlitsch, Roger W. Jones, David K. Hsu, John F. Mcclelland

Ames Laboratory Publications

Photoacoustic spectroscopy was used to predict the interlaminar shear strength of a carbon/epoxy composite. Samples were artificially aged by exposing the samples to elevated temperatures in an air environment. Short-beam shear tests were performed to determine mechanically the interlaminar shear strength of the samples. Photoacoustic spectra of the samples were also collected and compared to mechanical data. Chemometrics were performed on the spectral and mechanical data, and a good correlation was found between the near surface chemistry of the composite and overall mechanical integrity.


Pre-Impact Lower Extremity Posture And Brake Pedal Force Predict Foot And Ankle Forces During An Automobile Collision, Elizabeth C. Hardin, Anne Su, Antonie J. Van Den Bogert Dec 2004

Pre-Impact Lower Extremity Posture And Brake Pedal Force Predict Foot And Ankle Forces During An Automobile Collision, Elizabeth C. Hardin, Anne Su, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Background: The purpose of this study was to determine how a driver’s foot and ankle forces during a frontal vehicle collision depend on initial lower extremity posture and brake pedal force. Method of Approach: A 2D musculoskeletal model with seven segments and six right-side muscle groups was used. A simulation of a three-second braking task found 3647 sets of muscle activation levels that resulted in stable braking postures with realistic pedal force. These activation patterns were then used in impact simulations where vehicle deceleration was applied and driver movements and foot and ankle forces were simulated. Peak rearfoot ground ...


Environment Assisted Cracking Of Target Structural Materials Under Different Loading Conditions, Venkataramakrishnan Selvaraj Dec 2004

Environment Assisted Cracking Of Target Structural Materials Under Different Loading Conditions, Venkataramakrishnan Selvaraj

UNLV Theses, Dissertations, Professional Papers, and Capstones

Martensitic Alloy HT-9 has been tested for its evaluation of stress corrosion cracking resistance in neutral and acidic solutions at ambient and elevated temperatures incorporating smooth and notched cylindrical specimens under constant load and slow strain rate (SSR) conditions. C-ring and U-bend specimens have also been tested for stress corrosion cracking evaluation in the acidic solution. The role of hydrogen on the cracking tendency has been evaluated by cathodic applied potential.

The results of constant load testing enabled the determination of the threshold stress for stress corrosion cracking in susceptible environments. The magnitudes of ductility parameters were reduced with increasing ...


An Adaptive Tool-Based Telerobot Control System, Ge Zhang Dec 2004

An Adaptive Tool-Based Telerobot Control System, Ge Zhang

Doctoral Dissertations

Modern telerobotics concepts seek to improve the work efficiency and quality of remote operations. The unstructured nature of typical remote operational environments makes autonomous operation of telerobotic systems difficult to achieve. Thus, human operators must always remain in the control loop for safety reasons. Remote operations involve tooling interactions with task environment. These interactions can be strong enough to promote unstable operation sometimes leading to system failures. Interestingly, manipulator/tooling dynamic interactions have not been studied in detail. This dissertation introduces a human-machine cooperative telerobotic (HMCTR) system architecture that has the ability to incorporate tooling interaction control and other computer ...


Biomimetic Actuators: Where Technology And Cell Biology Merge [Review Article], Michael Knoblauch, Winfried Peters Nov 2004

Biomimetic Actuators: Where Technology And Cell Biology Merge [Review Article], Michael Knoblauch, Winfried Peters

Winfried S. Peters

The structural and functional analysis of biological macromolecules has reached a level of resolution that allows mechanistic interpretations of molecular action, giving rise to the view of enzymes as molecular machines. This machine analogy is not merely metaphorical, as bio-analogous molecular machines actually are being used as motors in the fields of nanotechnology and robotics. As the borderline between molecular cell biology and technology blurs, developments in the engineering and material sciences become increasingly instructive sources of models and concepts for biologists. In this review, we provide a – necessarily selective – summary of recent progress in the usage of biological and ...


Physical And Chemical Characteristics Of Commercially Available Brake Shoe Lining Materials: A Comparative Study Nov 2004

Physical And Chemical Characteristics Of Commercially Available Brake Shoe Lining Materials: A Comparative Study

A.S. Md Abdul Haseeb

The physical and chemical characteristics of four commercial automotive brake shoe lining materials used in heavy vehicles have been investigated and compared. Relevant physical properties viz. density, water absorption and swelling characteristics were determined using standard test methods. X-ray diffraction, infrared spectroscopy and optical microscopic techniques were used to identify the constituents. It has been observed that all of the four friction materials contain phenol formaldehyde resin as the matrix. Other major ingredients were also the same in all the samples but their amount and size varied. These include asbestos as fibre reinforcement, barium sulphate as filler and brass particles ...


Physical And Chemical Characteristics Of Commercially Available Brake Shoe Lining Materials: A Comparative Study Nov 2004

Physical And Chemical Characteristics Of Commercially Available Brake Shoe Lining Materials: A Comparative Study

A.S. Md Abdul Haseeb

The physical and chemical characteristics of four commercial automotive brake shoe lining materials used in heavy vehicles have been investigated and compared. Relevant physical properties viz. density, water absorption and swelling characteristics were determined using standard test methods. X-ray diffraction, infrared spectroscopy and optical microscopic techniques were used to identify the constituents. It has been observed that all of the four friction materials contain phenol formaldehyde resin as the matrix. Other major ingredients were also the same in all the samples but their amount and size varied. These include asbestos as fibre reinforcement, barium sulphate as filler and brass particles ...


Introduction To Mechanical Engineering, Lorik Abdullai, Joseph R. Dunn Nov 2004

Introduction To Mechanical Engineering, Lorik Abdullai, Joseph R. Dunn

Honors Theses

I can still remember back in high school when I was faced with a decision thousands of students experience every year: What college was I going to choose, and what major was I going to study? It seemed like every time I saw friends and relatives they asked me that question. Meanwhile, I knew that going to a major university would give me more choices in case I changed majors. As it turned out, Western Michigan University was the best package for me when I considered the financial aid, the program ofmy major, location of the university, and its friendly ...


Development Of Pole Impact Testing At Multiple Vehicle Side Locations As Applied To The Ford Taurus Structural Platform, Mark Halford Warner Nov 2004

Development Of Pole Impact Testing At Multiple Vehicle Side Locations As Applied To The Ford Taurus Structural Platform, Mark Halford Warner

Theses and Dissertations

A test method was developed whereby repeated pole impacts could be performed at multiple locations per test vehicle, allowing a comparison of energy and crush relationships. Testing was performed on vehicles moving laterally into a 12.75 inch diameter rigid pole barrier. Crush energy absorption characteristics at the different locations were analyzed, and the results compared to test data from broad moving barrier crashes and available crash tests with similar pole impacts. The research documents the crush stiffness characteristics for narrow impacts at various points on the side of the Taurus vehicle platform. Factors encountered during the research include the ...