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University of Arkansas, Fayetteville

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Articles 151 - 180 of 187

Full-Text Articles in Mechanical Engineering

Characterization Of Nano-Porous Si-Cu Composites To Enhance Lubricant Retention Impacting The Tribological Properties Of Sliding Surfaces, Julius Sheldon Morehead May 2015

Characterization Of Nano-Porous Si-Cu Composites To Enhance Lubricant Retention Impacting The Tribological Properties Of Sliding Surfaces, Julius Sheldon Morehead

Graduate Theses and Dissertations

As the expectations for modern machinery's tribological and thermal performances continue to rise, the retention of lubricant on the contact surfaces of their sliding components becomes an increasingly important issue. Friction and wear cause heat-related failures which lead to catastrophic damage to machinery. Evaporation of a lubricant's volatile constituents as well as lubricant migration leads not only to a reduction in lubricant quantity but also in its quality, thus facilitating component failures. In order to enhance component reliability, the surface should incorporate features that actively retain lubricants. The unique properties of nano-porous topographies such as their high surface area-to-volume ratio …


Three Dimensional Simulations Of Tornado Sheltering Effect Of Man-Made Structures, Piotr Gorecki May 2015

Three Dimensional Simulations Of Tornado Sheltering Effect Of Man-Made Structures, Piotr Gorecki

Graduate Theses and Dissertations

A three dimensional computational fluid dynamics (CFD) model was utilized to investigate tornado-like vortex interactions with wide man-made structures. The tornado-like wind profile was approximated using Rankine vortex model. By utilizing the CFD model, it was explained why tornadoes exhibit less damage on leeward side of large structures. During the preliminary stage of this study, a perpendicular vortex-prism interaction was analyzed. The prism height and the length were equal to the vortex core radius. The prism was also 12 times wider than the vortex core radius. During the vortex-prism interaction, the near-ground portion of the vortex was blocked by the …


Maximum Power Point Tracking And Solar Power For Developing Countries Around The World, Christopher M. Plate May 2015

Maximum Power Point Tracking And Solar Power For Developing Countries Around The World, Christopher M. Plate

Electrical Engineering Undergraduate Honors Theses

Renewable energy is becoming increasingly important as more and more countries become industrialized. Using solar power as opposed to fossil fuels and coal is becoming cheaper and easier to access throughout the world, yet there are still efficiency hurdles to be overcome. Designing a cheap, easily modifiable and reparable Maximum Power Point Tracker would be a stepping stone to bringing solar power to remote parts of the globe. Once designed and made portable, these devices could be distributed throughout developing countries to enhance renewable energy output. An Arduino-based tracker was chosen for ease of use and access. This base also …


Fusion Of Short-Mid Wavelength Infrared Image And Long Wavelength Image Using Discrete Wavelet Transform For Image Quality Enhancement, Rocky Hedrick May 2015

Fusion Of Short-Mid Wavelength Infrared Image And Long Wavelength Image Using Discrete Wavelet Transform For Image Quality Enhancement, Rocky Hedrick

Electrical Engineering Undergraduate Honors Theses

Infrared technology advancements have led to an expansive set of infrared applications in both the private and public sectors. New materials and manufacturing techniques have continued to reduce the cost while improving the quality of infrared cameras, but the cost is still high when compared to the cost versus quality of visible light spectrum cameras. Innovative image processing techniques can be implemented to help bridge this gap between the cost and quality of infrared cameras. The goal of this research is to improve the overall quality of infrared imaging by fusing short-mid wavelength infrared images and long wavelength images of …


Experimental Verification And Integration Of A Next Generation Smart Power Management System, Tavis Clemmer May 2015

Experimental Verification And Integration Of A Next Generation Smart Power Management System, Tavis Clemmer

Graduate Theses and Dissertations

With the increase in energy demand by the residential community in this country and the diminishing fossil fuel resources being used for electric energy production there is a need for a system to efficiently manage power within a residence. The Smart Green Power Node (SGPN) is a next generation energy management system that automates on-site energy production, storage, consumption, and grid usage to yield the most savings for both the utility and the consumer. Such a system automatically manages on-site distributed generation sources such as a PhotoVoltaic (PV) input and battery storage to curtail grid energy usage when the price …


Utilizing Failure Information For Mission Assessment And Optimization For Complex Systems, Charlie Destefano Dec 2014

Utilizing Failure Information For Mission Assessment And Optimization For Complex Systems, Charlie Destefano

Graduate Theses and Dissertations

This paper presents a new failure analysis method, Failure Identification for Mission Analysis (FIMA), which performs a general failure analysis for the overall state of a system, as well as a mission-specific analysis that identifies how failures may have differing effects on the various mission tasks that a system must complete. The FIMA method is capable of being implemented at any point in the design process. During early design stages, the FIMA method will identify various qualitative failure scenarios based on programmed functional relationships and any number of initial failures wished to be simulated. The functional relationships for this method …


Wear Resistant Polydopamine/Ptfe Nanoparticle Composite Coating For Dry Lubrication Applications, Samuel George Beckford Dec 2014

Wear Resistant Polydopamine/Ptfe Nanoparticle Composite Coating For Dry Lubrication Applications, Samuel George Beckford

Graduate Theses and Dissertations

This dissertation presents an investigation into the effect of nanoparticle fillers and a polydopamine adhesive primer on the tribological performance of thin PTFE films. The principal objective of this investigation was to reduce wear in PTFE films, an issue which precludes the use of PTFE films in tribological applications requiring high durability. The friction and wear of the composite films were evaluated using a ball-on-flat configuration in linear reciprocating motion. It was found that the use of a polydopamine adhesive primer reduces the wear of PTFE films more than 600 times. X-ray photoelectron spectroscopy (XPS) results show that a tenacious …


Highly Transparent, Self-Cleaning, And Antireflective Nanoparticle Coatings, Corey Seth Thompson Dec 2014

Highly Transparent, Self-Cleaning, And Antireflective Nanoparticle Coatings, Corey Seth Thompson

Graduate Theses and Dissertations

Current solar panel technologies require a sheet of glass to serve as both mechanical support and to protect the cells from the environment. The reflection from the glass sheet can reflect up to 8% of the incident light, reducing the power output of the panel. Antireflective coatings can be used to allow more light to enter the panel to be converted into usable electricity. However, no solid thin film materials exhibit a low enough index of refraction to serve as antireflective coatings for common solar glass. The main goal of this research was to investigate the self-cleaning, antifogging, and antireflective …


Atomistic Simulation And Virtual Diffraction Characterization Of Alumina Interfaces: Evaluating Structure And Stability For Predictive Physical Vapor Deposition Models, Shawn Patrick Coleman Aug 2014

Atomistic Simulation And Virtual Diffraction Characterization Of Alumina Interfaces: Evaluating Structure And Stability For Predictive Physical Vapor Deposition Models, Shawn Patrick Coleman

Graduate Theses and Dissertations

The objectives of this work are to investigate the structure and energetic stability of different alumina (Al2O3) phases using atomistic simulation and virtual diffraction characterization. To meet these objectives, this research performs molecular statics and molecular dynamics simulations employing the reactive force-field (ReaxFF) potential to model bulk, interface, and surface structures in the θ-, γ-, κ-, and α-Al2O3 system. Simulations throughout this study are characterized using a new virtual diffraction algorithm, developed and implemented for this work, that creates both selected area electron diffraction (SAED) and x-ray diffraction (XRD) line profiles without assuming …


Electroencephalography(Eeg) Data Collection And Processing Through Machine Learning, Jayshree Desai Aug 2014

Electroencephalography(Eeg) Data Collection And Processing Through Machine Learning, Jayshree Desai

Graduate Theses and Dissertations

Machine learning methods are an excellent way for understanding the neural basis of human decision making. Some machine learning systems try to eradicate the need for human intuition in data analysis whereas others embrace a collective approach between humans and machines. The objective of this project is to collect Electroencephalography (EEG) signals through wireless sensors, and the process the collected signals through machine learning methods. The EEG data is collected using three EEG electrodes, each being the positive, negative and ground terminals respectively. Since the signal measures in the unit of micro-volts it needs to be amplified using amplifier circuit. …


Phase Transformation In Monolayer Molybdenum Disulphide With And Without Defects Under Tension Predicted By Atomistic Simulations, Khanh Quoc Dang May 2014

Phase Transformation In Monolayer Molybdenum Disulphide With And Without Defects Under Tension Predicted By Atomistic Simulations, Khanh Quoc Dang

Graduate Theses and Dissertations

In addition to its use as a solid lubricant, molybdenum disulphide (MoS2) has gained recent attention as a possible substitute for silicon as it is increasingly difficult to keep shrinking down electronic devices made of silicon, the conventional electronic material. When thinned down to atomic thickness, monolayer MoS2 possesses very unique and promising electronic and electrical properties. Unlike electronic and electrical properties, knowledge of the mechanical properties and role of structural defects on these properties of monolayer MoS2 is unexplored. For this thesis, the two main objectives are (1) to gain insight about the failure mechanism of monolayer MoS2 by …


High Temperature Ltcc Based Sic Double-Sided Cooling Power Electronic Module, Hao Zhang May 2014

High Temperature Ltcc Based Sic Double-Sided Cooling Power Electronic Module, Hao Zhang

Graduate Theses and Dissertations

This objective of this dissertation research is to investigate a module packaging technology for high temperature double-sided cooling power electronic module application. A high-temperature wire-bondless low-temperature co-fired ceramic (LTCC) based double-sided cooling power electronic module was designed, simulated and fabricated. In this module, the conventional copper base plate is removed to reduce the thermal resistance between the device junctions to the heat sink and to improve the reliability of the module by eliminating the large area solder joint between the power substrate and the copper base plate. A low-temperature co-fired ceramic (LTCC) substrate with cavities and vias is used as …


Crack Growth Behavior Under Creep-Fatigue Conditions Using Compact And Double Edge Notch Tension-Compression Specimens, Santosh B. Narasimha Chary Dec 2013

Crack Growth Behavior Under Creep-Fatigue Conditions Using Compact And Double Edge Notch Tension-Compression Specimens, Santosh B. Narasimha Chary

Graduate Theses and Dissertations

The American Society for Testing and Materials (ASTM) has recently developed a new standard for creep-fatigue crack growth testing, E 2760-10, that supports testing compact specimens, C(T), under load controlled conditions. C(T) specimens are commonly used for fatigue and creep-fatigue crack growth testing under constant-load-amplitude conditions. The use of these specimens is limited to positive load ratios. They are also limited in the amount of crack growth data that can be developed at high stress intensity values due to accumulation of plastic and/or creep strains leading to ratcheting in the specimen. Testing under displacement control can potentially address these shortcomings …


Development Of A Pdms Based Micro Total Analysis System For Rapid Biomolecule Detection, Balaji Srinivasan Venkatesh May 2013

Development Of A Pdms Based Micro Total Analysis System For Rapid Biomolecule Detection, Balaji Srinivasan Venkatesh

Graduate Theses and Dissertations

The emerging field of micro total analysis system powered by microfluidics is expected to revolutionize miniaturization and automation for point-of-care-testing systems which require quick, efficient and reproducible results. In the present study, a PDMS based micro total analysis system has been developed for rapid, multi-purpose, impedance based detection of biomolecules. The major components of the micro total analysis system include a micropump, micromixer, magnetic separator and interdigitated electrodes for impedance detection. Three designs of pneumatically actuated PDMS based micropumps were fabricated and tested. Based on the performance test results, one of the micropumps was selected for integration. The experimental results …


Design And Fundamental Understanding Of Minimum Quantity Lubrication (Mql) Assisted Grinding Using Advanced Nanolubricants, Parash Kalita May 2013

Design And Fundamental Understanding Of Minimum Quantity Lubrication (Mql) Assisted Grinding Using Advanced Nanolubricants, Parash Kalita

Graduate Theses and Dissertations

Abrasive grinding is widely used across manufacturing industry for finishing parts and components requiring smooth superficial textures and precise dimensional tolerances and accuracy. Unlike any other machining operations, the complex thermo-mechanical processes during grinding produce excessive friction-induced energy consumption, heat, and intense contact seizures. Lubrication and cooling from grinding fluids is crucial in minimizing the deleterious effects of friction and heat to maximize the output part quality and process efficiency. The conventional flood grinding approach of an uneconomical application of large quantities of chemically active fluids has been found ineffective to provide sufficient lubrication and produces waste streams and pollutants …


Development Of Mems-Based Corrosion Sensor, Feng Pan Dec 2012

Development Of Mems-Based Corrosion Sensor, Feng Pan

Graduate Theses and Dissertations

This research is to develop a MEMS-based corrosion sensor, which is used for monitoring uniform, galvanic corrosion occurring in infrastructures such as buildings, bridges. The corrosion sensor is made up of the composite of micro/nano metal particles with elastomers. The mechanism of corrosion sensor is based on the mass transport of corrosive species through the sensor matrix. When the metal particles in the matrix corrode, the electrical resistivity of the material increases due to increasing particle resistances or reduction of conducting pathways. The corrosion rate can be monitored by detecting the resistivity change in sensing elements. The life span of …


Silica Nanoparticle-Based Coatings With Superhydrophilic And Superhydrophobic Properties, Robert Andrew Fleming Dec 2012

Silica Nanoparticle-Based Coatings With Superhydrophilic And Superhydrophobic Properties, Robert Andrew Fleming

Graduate Theses and Dissertations

Superhydrophilic and superhydrophobic surfaces have potential for implementation into a variety of fields, including self-cleaning surfaces, anti-fogging transparent materials, and biomedical applications. In this study, sandblasting, oxygen plasma treatments, silica nanoparticle films, and a low surface energy fluorocarbon film were employed to change the natural surface wettability of titanium, glass, and polyethylene terephthalate (PET) substrates, with an aim to produce superhydrophilic and superhydrophobic behavior. The effects of these surface modifications are characterized by water contact angles (WCAs), surface wetting stability, surface morphology and roughness, surface elemental composition, and optical transmittance measurements. The results show that stable superhydrophilic and superhydrophobic surfaces …


Distribution Map Of Multi-Walled Carbon Nanotubes In A Refrigerant/Oil Mixture Within A 2.5 Ton Unitary Air-Conditioner, Warren Russell Long Dec 2012

Distribution Map Of Multi-Walled Carbon Nanotubes In A Refrigerant/Oil Mixture Within A 2.5 Ton Unitary Air-Conditioner, Warren Russell Long

Graduate Theses and Dissertations

In recent years, nanoparticles have received considerable attention as a potential additive to heat transfer fluids (i.e. refrigerant) in order to increase the heat transfer capabilities of these fluids. The potential of carbon nanotubes (CNTs) to exit the compressor, migrate throughout a vapor compression air conditioning system, and possibly foul the components of such a system was experimentally investigated in this research. Six grams of CNTs were dispersed in the polyol ester oil used by a 2.5 ton (8.79 kW) unitary air conditioning system, which was continuously operated for 168 hours. After this time, the unit was shut down and …


Design, Fabrication, Testing Of Cnt Based Isfet And Characterization Of Nano/Bio Materials Using Afm, Zhuxin Dong Dec 2012

Design, Fabrication, Testing Of Cnt Based Isfet And Characterization Of Nano/Bio Materials Using Afm, Zhuxin Dong

Graduate Theses and Dissertations

A combination of Carbon Nanotubes (CNTs) and Ion Selective Field Effect Transistor (ISFET) is designed and experimentally verified in order to develop the next generation ion concentration sensing system. Micro Electro-Mechanical System (MEMS) fabrication techniques, such as photolithography, diffusion, evaporation, lift-off, packaging, etc., are required in the fabrication of the CNT-ISFET structure on p-type silicon wafers. In addition, Atomic Force Microscopy (AFM) based surface nanomachining is investigated and used for creating nanochannels on silicon surfaces. Since AFM based nanomanipulation and nanomachining is highly controllable, nanochannels are precisely scratched in the area between the source and drain of the FET where …


Computational Design Of The Electrical And Mechanical Performance Of Steerable Mems Antennas, Morgan Andrew Roddy Dec 2012

Computational Design Of The Electrical And Mechanical Performance Of Steerable Mems Antennas, Morgan Andrew Roddy

Graduate Theses and Dissertations

This thesis describes the origins, improvements, and variations of a broadband microwave antenna that can be beam-steered by a micro-electromechanical system (MEMS). The steerable MEMS antenna of this work was comprised of a planar antenna on top of a Silicon membrane. The membrane is etched to create a gimbal hinge structure and a platform which supported the antenna and gave it one or two degrees of freedom of rotation. The antennas presented were broadband and fed by a coplanar waveguide (CPW) transmission line which traversed the hinge structure. The antenna's orientation in space was designed to be changed through electrostatic …


Computer Modeling Of The Influence Of Structure Plan Areas On Tornado Forces, Nashmi Hassan M Alrasheedi May 2012

Computer Modeling Of The Influence Of Structure Plan Areas On Tornado Forces, Nashmi Hassan M Alrasheedi

Graduate Theses and Dissertations

The study of the conventional Straight Line (SL) wind flow dominates research into wind loads on structures. Most structure design takes into account only research into SL flow. Few researchers have studied tornado forces on buildings and attempted to distinguish between tornadic wind loads and SL flow loads. Using a computer simulation, this research addresses and distinguishes between the tornadic forces and SL forces on structures. In the numerical simulation, tornado forces and SL forces will be compared on large structure plan areas and on thin structure plan areas. Additionally this research investigates how the increase in the vortex strength …


Design And Implementation Of A Small Electric Motor Dynamometer For Mechanical Engineering Undergraduate Laboratory, Aaron Farley May 2012

Design And Implementation Of A Small Electric Motor Dynamometer For Mechanical Engineering Undergraduate Laboratory, Aaron Farley

Graduate Theses and Dissertations

This thesis set out to design and implement a new experiment for use in the second lab of the laboratory curriculum in the Mechanical Engineering Department at the University of Arkansas in Fayetteville, AR. The second of three labs typically consists of data acquisition and the real world measurements of concepts learned in the classes at the freshman and sophomore level. This small electric motor dynamometer was designed to be a table top lab setup allowing students to familiarize themselves with forces, torques, angular velocity and the sensors used to measure those quantities, i.e. load cells and optical encoders. The …


Design Of Orbital Maneuvers With Aeroassisted Cubesatellites, Stephanie Clark May 2012

Design Of Orbital Maneuvers With Aeroassisted Cubesatellites, Stephanie Clark

Graduate Theses and Dissertations

Recent advances within the field of cube satellite technology has allowed for the possible development of a maneuver that utilizes a satellite's Low Earth Orbit (LEO) and increased atmospheric density to effectively use lift and drag to implement a noncoplanar orbital maneuver. Noncoplanar maneuvers typically require large quantities of propellant due to the large delta-v that is required. However, similar maneuvers using perturbing forces require little or no propellant to create the delta-v required. This research reported here studied on the effects of lift on orbital changes, those of noncoplanar types in particular, for small satellites without orbital maneuvering thrusters. …


Energy Consumption And Greenhouse Gas Emissions From Commercial And Manufacturing Sectors Specific Studies On Hvac Equipment And Dairy Processing, Aik Jong Tan May 2012

Energy Consumption And Greenhouse Gas Emissions From Commercial And Manufacturing Sectors Specific Studies On Hvac Equipment And Dairy Processing, Aik Jong Tan

Graduate Theses and Dissertations

Commercial and manufacturing sectors in United States consumed approximately 50% of the total End use energy in 2010. In 2009, 81.5% of the greenhouse gas (GHG) emitted in the United States was energy related. From the broad aspects of commercial and manufacturing sectors; two relatively narrow and specific topics, commercial building's HVAC equipment and dairy processing were chosen to increase the understanding of the energy use and GHG emission in these two sectors. Few published studies related to these two specific areas are available. The first study in this thesis discussed the energy use and GHG emissions by HVAC equipment …


A Study On The Effects Of Solar Power, Jonathan Hayes May 2012

A Study On The Effects Of Solar Power, Jonathan Hayes

Electrical Engineering Undergraduate Honors Theses

The utilization of new and alternative energy sources, specifically solar energy, has been on the rise and will continue to grow as we attempt to diminish our use and dependency on older, nonrenewable energy sources. One of the biggest challenges involved with the use of solar energy, or renewable energy in general, is how to provide this energy for general public use. Some of the limiting factors to this are the efficiency in which solar power can be harvested and converted into usable energy, and the cost of the technology to do this. Recent technological developments have included the microinverter, …


Surface Wetting And Friction Studies Of Nano-Engineered Surfaces On Copper Substrate, Julius Sheldon Morehead Dec 2011

Surface Wetting And Friction Studies Of Nano-Engineered Surfaces On Copper Substrate, Julius Sheldon Morehead

Graduate Theses and Dissertations

Nano-engineered-textures on a material surface can dramatically improve the wetting and non-wetting properties of a surface, and they also show promise to address friction issues that affect surfaces in contact. In this work, aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was used to produce nano-textures on copper (Cu) substrates. A study was performed to examine the effects of changing the annealing conditions and a-Si thickness on nano-texture formation. The creation of various nano-topographies and chemically modifying them using octafluorocyclobutane (C4F8) was performed to control hydrophilicity, hydrophobicity, and oil affinity of nano-textured surfaces. A video-based contact angle measurement system was used …


Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown Dec 2011

Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown

Graduate Theses and Dissertations

The past couple of decades have shown a concern when considering the way the world obtains its power. The focus has been switching from fossil fuels that have been used for hundreds of years to renewable energy sources, such as the sun. Solar energy is readily and infinitely available for harnessing. One problem with solar energy, though, is its inability to be used during the night time and during cloud covered weather. A solution to this problem is the use of energy storage mechanisms. For solar plants that use solar thermal energy (concentrating solar power plants), thermal energy storage (TES) …


Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans Dec 2011

Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans

Graduate Theses and Dissertations

The thermal demands of modern day electronic systems require innovative thermal solutions. Spray cooling has proven to be able to cool heat fluxes orders of magnitude higher than traditional cooling methodologies. This work includes a comparison of spray cooling to standard thermal management methodologies. Key system parameters and considerations are discussed. The properties of available packaging materials and their effect on the reliability of a spray cooled system are presented. Parameters such as fluid temperature, droplet size, fluid velocity and flow rate all directly impact performance and are detailed in this work. Finally, results from of a wide range of …


Understanding The Role Of A Bio-Inspired Surface Modification For Delayed Icing, Clayton Schenk Aug 2011

Understanding The Role Of A Bio-Inspired Surface Modification For Delayed Icing, Clayton Schenk

Graduate Theses and Dissertations

Atmospheric icing event is problematic for outdoor structures because it can damage, slow, impede, and danger general routine. For a wind turbine blade, it can damage, disrupt movement, and cause potentially dangerous ice throw. Anti-icing based on a surface texture is advantageous due to the low cost of maintenance and there is no additional requirement of energy output for preventing the icing problem. This work is based on the biomimicry of the superhydrophobic nature of the lotus leaf, whereas the limited wettability supports the water to flow freely from the surface structure. The phenomenon is based on a morphology and …


A Solid State Nitrogen Gas Generating Chip And Applications For Picosatellites, Kyle Godin Aug 2011

A Solid State Nitrogen Gas Generating Chip And Applications For Picosatellites, Kyle Godin

Graduate Theses and Dissertations

A microscale gas generating chip has many applications; in this study, applications relating to picosatellites have been considered. Cube satellites, a type of picosatellite, are of mass around one kilogram and side length 10cm x 10cm x 10cm. Their launches are becoming more numerous since their debut ten years ago. Their low cost and deployment system makes space accessible to agencies hitherto barred from it, such as universities and small governments. However, their power, mass, and volume budget is extremely tight. A microscale gas chip could compete with other designs for attitude control devices, most not flown yet as cube …