Mechanical Engineering Commons^™

Manufacturing Of Single Solid Oxide Fuel Cells, Jonathan Torres-Caceres

Electronic Theses and Dissertations

Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable. The …

Three-Phase Contact Line Phenomena In Droplets On Solid And Liquid Surfaces: Electrocapillary, Pinning, Wetting Line Velocity Effect, And Free Liquid Surface Deformation, Roxana Shabani

Electronic Theses and Dissertations

In this dissertation physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wetting line) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL) phenomena which encompass the wetting line energy (WLE) or pinning, the wetting line velocity (WLV), and the contact angle hysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the interfacial phenomena such as the air film lubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium …

Nanofibers Reinforced Polymer Composite Microstructures, Andy Alubaidy, Krishnan Venkatakrishnan, Bo Tan

Books and Websites

The book Advances in Nanofibers is a research publication that covers original research on developments within the Nanofibers field of study. The book is a collection of reviewed scholarly contributions written by different authors. Each scholarly contribution represents a chapter and each chapter is complete in itself but related to the major topics and objectives. The target audience comprises scholars and specialists in the field.

Chapter 7 "Nanofibers Reinforced Polymer Composite Microstructures," by Andy Alubaidy, Krishnan Venkatakrishnan, and Bo Tan is designed to be a comprehensive source for nanofibers reinforced polymer studies. The fundamental properties, manufacturing techniques, and applications of …

Mode And Implementation Of A Hybrid Control System For A 2-Mode Hybrid Electric Vehicle, Zhenhua Zhu

Graduate Theses, Dissertations, and Problem Reports

Automotive transportation consumes more than 71% of the world's total petroleum energy. The vehicle will have to use less because it will take less than 30 years to consume the rest of the proven conventional oil reservoir if the fuel consumption keeps the current trend. One of the methods to improve the vehicle efficiency is to develop Hybrid Electric Vehicle (HEV). An HEV combines an internal combustion engine (ICE) and electric motor(s) powered by batteries or capacitors to achieve better fuel economy. Among the HEVs, 2-Mode HEV combines an ICE and two electric motors with two planetary gear sets and …

Enhanced Purity Andresolution Via Laser Assistedelectron Beam Induced Deposition Of Platinum,, Nick A. Roberts, J. D. Fowlkes, G. A. Magel, P. D. Rack

Nick Roberts

We introduce a laser assisted electron beam induced deposition (LAEBID) process which is a nanoscale direct write synthesis method that integrates an electron beam induced deposition process with a synchronized pulsed laser step to induce thermal desorption of reaction by-products. Localized, spatially overlapping electron and photon pulses enable the thermal desorption of the reaction by-product while mitigating issues associated with bulk substrate heating, which can shorten the precursor residence time and distort pattern fidelity due to thermal drift. Current results demonstrate purification of platinum deposits (reduced carbon content by ~50%) with the addition of synchronized laser pulses as well as …

Assess The Accuracy Of The Variational Asymptotic Plate And Shell Analysis Using The Generalized Uni, Luciano Demasi, Wenbin Yu

Mechanical and Aerospace Engineering Faculty Publications

The accuracy of the Variational Asymptotic Plate and Shell Analysis (VAPAS) is assessed against several higher order, zig zag and layerwise theories generated by using the invariant axiomatic framework denoted as Generalized Unified Formulation (GUF). These theories are also compared against the elasticity solution developed for the case of a sandwich structure with high Face to Core Stiffness Ratio. GUF allows to use an infinite number of axiomatic theories (Equivalent Single Layer theories with or without zig zag effects and Layerwise theories as well) with any combination of orders of the displacements and it is an ideal tool to precisely …

Thermal Conductivity Profile Determination In Proton-Irradiated Zrc By Spatial And Frequency Scanning Thermal Wave Methods, C. Jensen, M. Chirtoc, N. Horny, J. S. Antoniow, H. Pron, Heng Ban

Mechanical and Aerospace Engineering Faculty Publications

Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 °C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the …

Binaural Room Impulse Response Database Acquired From A Variable Acoustics Classroom, Zhao Peng, Siu Kit Lau, Lily M. Wang, Sean Browne, Kenneth P. Roy

Durham School of Architectural Engineering and Construction: Faculty Publications

Room measurements were conducted in a variable acoustics classroom mockup space (epod) at Armstrong World Industries in Lancaster, Pennsylvania, USA. Binaural room impulse responses were measured in the epod using a head and torso simulator. Five reverberation time (RT) scenarios were achieved with various combinations of absorptive wall panels and acoustical ceiling tile. These provided a range of mid-frequency RTs from 0.4 to 1.1 seconds. Three of the five RT scenarios were achieved using two different material configurations to also consider material location effects. For each of the eight material configurations, two student-teacher orientations were tested. One orientation had all …

Thermal Characterization Of As4/3501-6 Carbon-Epoxy Composite, Bradley R. Doleman

Theses

Thermal diffusivity, specific heat, and thermal conductivity are important thermophysical properties of composite materials and foams. Thermal characterization provides these material properties which play a significant role in the engineering design process of space systems, aerospace vehicles, transportation, energy storage devices, and power generation including fuel cells. Thermal conductivity is the parameter that is important in problems involving heat transfer and thermal structures. Because it determines the working temperature levels of a material, the thermal conductivity is critical when considering the performance of materials in high temperature applications as well as safety, process control, and quality assurance. As a result …

Carbon Dioxide Absorption And Channelling In Closed Circuit Rebreather Scrubbers, Shona Cunningham

Theses

Closed Circuit Rebreathers (CCRs) are a type of Self Contained Underwater Breathing Apparatus (SCUBA) used predominantly by the diving community. CCR technologies have become prevalent within the commercial, military and technical diving communities over recent years. CCRs work by recycling breathing gas, by-passing the gas through a carbon dioxide (CO₂) chemical scrubber and topping the resultant scrubbed gas up with pure oxygen to maintain the oxygen content at a level which supports life. One of the main dangers currently faced by divers using this equipment is the risk of CO₂ poisoning if the scrubber fails. This failure …

Enhanced Tribological Properties Of Surfaces Patterned With Su8/Dlc Microstructures, Luke Osborn

Inquiry: The University of Arkansas Undergraduate Research Journal

In tribology (the study of friction, wear, and lubrication), it is known that micro-textured surfaces can reduce friction due to decreased contact area between two surfaces. The problem with many micro-textures, however, is their inability to withstand significant amounts of wear, thus limiting their potential uses and overall effectiveness. In this study, connected and isolated microstructures of SU8, a negative tone photoresist, coated with and without diamond-like carbon (DLC), were designed to investigate the effects of these microstructures and DLC coating on the tribological performance of a surface. Friction and wear studies were conducted using a tribometer; surface topography and …

Dynamic Contact Analysis Of A Piezoelectrically Driven Ultrasonic Crawler-Actuator, Dwight Santiago Maness

Masters Theses

"A standing wave ultrasonic motor (SWUM) is presented in this thesis. The actuator is piezoelectrically powered and operates in the first and second bending modes to move forwards and backwards, respectively. The kinematic stability of the crawler, backed by experimental results is shown in the first paper presented in this thesis. This study demonstrates that in the absence of a preload or kinematic constraints, the crawler shows vertical stability. A full transient analysis using the finite element method is performed characterizing the speed and contact variables is conducted in the second paper. The results show that given enough time the …

Development Of Dynamic Thermal Performance Metrics For Eco-Roof Systems, Seth Sinclair Moody

Dissertations and Theses

In order to obtain credit for an eco-roof in building energy load calculations the steady state and time-varying thermal properties (thermal mass with evapotranspiration) must be fully understood. The following study presents results of experimentation and modeling in an effort to develop dynamic thermal mass performance metrics for eco-roof systems. The work is focused on understanding the thermal parameters (foliage & soil) of an eco-roof, further validation of the EnergyPlus Green Roof Module and development of a standardized metric for assessing the time-varying thermal benefits of eco-roof systems that can be applied across building types and climate zones. Eco-roof foliage, …

Near Wall Shear Stress Modification Using An Active Piezoelectric Nanowire Surface, Christopher R. Guskey

Theses and Dissertations--Mechanical Engineering

An experimental study was conducted to explore the possible application of dynamically actuated nanowires to effectively disturb the wall layer in fully developed, turbulent channel flow. Actuated nanowires have the potential to be used for the mixing and filtering of chemicals, enhancing convective heat transfer and reducing drag. The first experimental evidence is presented suggesting it is possible to manipulate and subsequently control turbulent flow structures with active nanowires. An array of rigid, ultra-long (40 μm) TiO₂ nanowires was fabricated and installed in the bounding wall of turbulent channel flow then oscillated using an attached piezoelectric actuator. Flow velocity …

Dnad, A Simple Tool For Automatic Differentiation Of Fortran Codes Using Dual Numbers, Wenbin Yu, Maxwell Blair

Mechanical and Aerospace Engineering Faculty Publications

DNAD (dual number automatic differentiation) is a simple, general-purpose tool to automatically differentiate Fortran codes written in modern Fortran (F90/95/2003) or legacy codes written in previous version of the Fortran language. It implements the forward mode of automatic differentiation using the arithmetic of dual numbers and the operator overloading feature of F90/95/2003. Very minimum changes of the source codes are needed to compute the first derivatives of Fortran programs. The advantages of DNAD in comparison to other existing similar computer codes are its programming simplicity, extensibility, and computational efficiency. Specifically, DNAD is more accurate and efficient than the popular complex-step …

A Novel Resistance Exercise Machine For Use In A Lower Body Negative Pressure Box To Counteract The Effects Of Weightlessness, Christine M. Dailey

Doctoral Dissertations and Master's Theses

Physiological deconditioning is a critical problem in space, especially during long-term missions. Resistance exercise coupled with lower body negative pressure (LBNP) has been shown to be effective in counteracting some of the deconditioning related problems. This thesis describes the development of a compact and effective resistance exercise machine that works within an existing environmentally controlled LBNP Box and is designed to simulate both exercise and sitting, to prevent microgravity-induced deconditioning by simulating physiological and biomechanical features of upright exercise and daily activities. Theoretical calculations are carried out to determine whether kinematics, musculoskeletal loadings, and metabolic rate during supine exercise within …

Process Study And Control Of Electron Beam Melting Technology Using Infrared Thermography, Jorge Mireles

Open Access Theses & Dissertations

An IR camera was installed in an Arcam A2 system (Arcam AB, Mölndal, Sweeden) and layer-by-layer image acquisition was achieved. The camera's capability to detect manufacturing defects was evaluated by implementing computer vision techniques using LabVIEW measurement and programming software (National Instruments, Austin, TX). Thermal maps acquired by the IR camera allowed layer-by-layer part temperature to be recorded. A core objective of this research was to study the impact of processing temperature on EBM-fabricated Ti-6Al-4V parts and achieve controlled mechanical properties. In this research, build variations were achieved by modifying parameters that change processing temperature from the standard processing temperature. …

A Block Operator Splitting Method For Heterogeneous Multiscale Poroelasticity, Paul M. Delgado

Open Access Theses & Dissertations

Traditional models of poroelastic deformation in porous media assume relatively homogeneous material properties such that macroscopic constitutive relations lead to accurate results. Many realistic applications involve heterogeneous material properties whose oscillatory nature require multiscale methods to balance accuracy and efficiency in computation.

The current study develops a multiscale method for poroelastic deformation based on a fixed point iteration based operator splitting method and a heterogeneous multiscale method using finite volume and direct stiffness methods. To characterize the convergence

of the operator splitting method, we use a numerical root finding algorithm to determine a threshold surface in a non-dimensional parameter space …

Assessment Of Abaqus Capabilities For Crack Growth And Calculation Of Energy Release Rate, Luis Alonso Hernandez

Open Access Theses & Dissertations

The purpose of this study was to benchmark ABAQUS modeling capabilities for crack propagation and calculation of energy release rate against closed-form analytical solutions. The crack growth capability for this study was evaluated using the following techniques: virtual crack closure technique (VCCT), X-FEM coupled with VCCT, and X-FEM coupled with cohesive segments. The capability of calculating the energy release rate was assessed by using the J-integral routine. A Double Cantilever Beam (DCB) specimen was used to conduct the study for mode I propagation, and a mixed mode bending (MMB) specimen was used to study the propagation for mixed mode I/II …

Trajectory Generation For Stair Ascent Walking Using Rayleigh Oscillator, T. Afzal, Andrew B. Wright, Kamran Iqbal

Journal of the Arkansas Academy of Science

This paper describes a trajectory generation technique for stair-ascent walking. The knee, hip and ankle joint trajectory during stair ascent are generated using mutually coupled, nonlinear oscillators. The parameters of the oscillators are tuned using the harmonic balance method, which converts the nonlinear differential equations to a set of algebraic equations. Fourier analysis of data generated by stair-ascent walking is performed to extract the amplitude and the phase of the dominant frequency components for each joint trajectory. The solution for the oscillator is assumed to be a sinusoidal wave and then by harmonic balance method the parameters of the oscillator …