Mechanical Engineering Commons^™

Shield Design For Maximum Deformation In Shape-Shifting Surfaces, Daniel Eduardo Perez

USF Tampa Graduate Theses and Dissertations

This research presents the initial studies and results on shield design for Shape-Shifting Surfaces (SSSs) seeking maximum compression and maximum expansion of a unit-cell. Shape-Shifting Surfaces (SSSs) are multilayered surfaces that are able to change shape while maintaining their integrity as physical barriers. SSSs are composed of polygonal unit-cells, which can change side lengths and corner angles. These changes are made possible by each side and corner consisting of at least two different shields, or layers of material. As the layers undergo relative motion, the unit-cell changes shape. In order for the SSS to retain its effectiveness as a barrier, …

Supercritical Co2 Brayton Cycles For Solar-Thermal Energy, Brian D. Iverson, Thomas M. Conboy, James J. Pasch, Alan M. Kruizenga

Faculty Publications

Of the mechanisms to improve efficiency for solar-­‐thermal power plants, one of the most effective ways to improve overall efficiency is through power cycle improvements. As increases in operating temperature continue to be pursued, supercritical CO2 Brayton cycles begin to look more attractive despite the development costs of this technology. Further, supercritical CO2 Brayton has application in many areas of power generation beyond that for solar energy alone.

One challenge particular to solar-­‐thermal power generation is the transient nature of the solar resource. This work illustrates the behavior of developmental Brayton turbomachinery in response to a fluctuating thermal input, much …

Molten Carbonates As An Effective Oxygen Reduction Catalyst For 550–650°C Solid Oxide Fuel Cells, Yunhui Gong, Xue Li, Lingling Zhang, Whitney Tharp, Changyong Qin, Kevin Huang

Faculty Publications

We report the first study that investigates the use of molten carbonates as an effective catalyst to promote electrochemical oxygen reduction reaction (ORR) at the cathode of intermediate temperature solid oxide fuel cells (IT-SOFCs). A series of binary Li-K carbonate compositions were incorporated into the porous backbones of a commercial cathode assembled in symmetrical impedance cells for electrochemical characterization. Within the temperature range of 550–650◦C, we observed that the polarization and ohmic area-specific resistances of the original sample can be significantly reduced by the introduction of molten carbonates. A new ORR charge-transfer model involving two intermediate species CO5 2− and …

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 …

Metal-Based Microchannel Heat Exchangers : Manufacturing And Heat Transfer Testing, Bin Lu

LSU Doctoral Dissertations

This dissertation focuses on improving the functionality of metal-based microchannel heat exchangers (MHEs), as well as pushing this technology toward real-world applications. Design optimization was carried out on MHEs for performance maximization. Double-layered microchannel layout was experimentally studied, and a significant reduction on liquid flow pressure drop penalty was achieved. Other than water, another commonly-used coolant, ethylene glycol, was applied to MHEs, and flow and heat transfer characteristics were quantified. Transient Liquid Phase (TLP) bonding was used for joining Cu structures. For further understanding of the MHE heat transfer, a detailed examination was carried out on the TLP bonding interface …

A Study On The Cleaning And Modification Of Metal Surfaces By Direct Current Cathodic Electrolytic Plasma Process, Jiandong Liang

LSU Doctoral Dissertations

The processes of surface treatments or surface modifications, more formally known as surface engineering, tailor the surfaces of engineering materials. The treatments are usually intended to change physical properties such as thermal or electrical conductivity, modify the surface dimensions, i.e. roughness, etc. A novel surface treatment method, Electrolytic Plasma Process (EPP), was developed for coating purposes, in its early developmental stage. In this work, the major effort is to avoid using any environmental hazardous chemical (coatings) and to extend such its application to some new fields. The general response of the substrate material under electrolytic plasma process was summarized including …

Generalizable Methods For Modeling Lumbar Spine Kinematics, Craig Joseph Simons

Electronic Theses and Dissertations

A more complete understanding of lumbar spine kinematics could improve diagnoses and treatment of low back pathologies and may advance the development of biomechanical models. Kinematics describes motion of the five lumbar vertebrae without consideration for the forces that cause the motion. Despite considerable attention from researchers and clinicians, lumbar spine kinematics are not fully understood because the anatomy is not accessible for direct observation and the complex governing biomechanics produce small magnitude, coupled intervertebral movements.

The overall goal of this project was to develop a descriptive model of intervertebral lumbar spine kinematics that is applicable to a generalizable subject …

Modeling Ultrasonic Field Emanating From Scanning Acoustic Microscope For Reliable Characterization Of Pathogens (Biological Materials), Rowshan Ara Rima

Theses and Dissertations

Acoustic microscopy provides extraordinary advantages over state-of-the-art invasive imaging techniques to determine the mechanical properties of living colonies of pathogens and micro-organisms. It is possible to obtain the morphomechanical parameters of the pathogenic colonies e.g. variation of thickness, stiffness and the coefficients of attenuation, using scanning acoustic microscope (SAM). However, the process requires an expert with extensive understanding of SAM and ultrasonic signals which is very time consuming and expensive for complex form of analysis. Due to lack of a suitable computational tool, presently the ultrasonic wave scattering, reflection and transmission through the biological specimens cannot be properly visualized. Without …

Improved Limits And Portability Over Currently Employed Cadmium Monitoring Systems Through Preconcentration For Detection By Way Of Micro-/Nanofluidic Mechanisms, Paul F. Wach

Theses and Dissertations

Due to risk of environmental and biological accumulation of Cadmium (Cd), improved methods of early detection and monitoring must be explored as a preventative measure. Listed as one of the top three toxic heavy metals by the Environmental Protection Agency (EPA), the effects on ecological and human systems have well documented side-effects of physical mutation, reproductive sterility, kidney failure, liver disease, bone loss, and death. Found in batteries, metal plating, pigments, plastics, and cigarettes, Cd is also used as a neutron absorber in the nuclear industry as well as having 3 known radioactive isotopes. Urine Cd levels, which have been …

Numerical Study Of Stable Tearing Crack Growth Events Using The Cohesive Zone Model Approach, Xin Chen

Theses and Dissertations

Numerical analysis of stable tearing crack growth events plays an important role in assessing the structural integrity and residual strength of critical engineering structures. The cohesive zone model (CZM) has been widely applied to simulate fracture processes in a variety of material systems. However, its application to the study of elastic-plastic stable tearing crack growth events in ductile materials, especially under mixed-mode loading conditions, has been limited. The current study is aimed at investigating the applicability of the CZM based approach in simulating mixed-mode stable tearing crack growth events in aluminum alloys. In the simulations, which are carried out using …

Structural Origin Of Mechanical Prowess In Conch Shells, Haoze Li

Theses and Dissertations

Conch shells are natural nanocomposites with an exquisite multiscale hierarchical architecture which exhibit coupled ultrahigh mechanical strength and toughness. What materials design strategy renders conch shells such mechanical prowess? In this study, micro/nanoscale structural and mechanical characterization of conch shells (Busycon carica) has been carried out. We demonstrate, for the first time, direct evidence that the previously claimed single-crystal third-order lamellae - the basic building blocks in conch shells are essentially assembled with aragonite nanoparticles of the size ranging from 20 to 45 nm. The third-order lamellae exhibit not only elasticity but also plasticity with the strain up to 0.7% …

Synthesis And Characterization Of One Dimensional Boron-Based Nanomaterials, Rui Li

Theses and Dissertations

One dimensional (1D) metal borate and boride nanomaterials have attracted tremendous attention due to their good chemical inertness, high-temperature stability, excellent mechanical properties, and low thermal expansion coefficient.

Beta-BaB2O4 (BBO) is a well-known nonlinear optical material with a high second-order nonlinear susceptibility, wide transparency range, and high damage threshold. Using a low temperature, organic-free hydrothermal technique, single-crystalline barium polyborate Ba3B6O9(OH)6 (BBOH) nanorods were synthesized. It was found that BBO nanospindles can be achieved by annealing the BBOH nanorods at a relatively low temperature of 810 oC. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were …

Dual-Phase Mixed Ion And Electron Conducting Co2-Selective Permeation Membranes, Lingling Zhang

Theses and Dissertations

Fossil fuels are the dominant energy source powering our modern society. However, burning fossil fuels emits carbon dioxide (CO2), a greenhouse gas that can cause climate change and ultimately threaten the survival of humanity. Effectively mitigating CO2 emissions from the use of fossil fuels has become an intense subject of scientific research as well as political debate in recent years. The current mainstream technical approach to achieving that goal is to curb the emission of CO2 by capturing CO2 at point-sources and geologically storing it. The CO2 separation and capture process, the first step toward the ultimate storage of CO2, …

Environmental Effects On Mechanical And Thermal Behaviors Of Zinc Oxide Nanobelts And Dispersion Of Carbon Nanostructures, Yingchao Yang

Theses and Dissertations

One-dimensional (1-D) nanostructures, such as nanowires, nanobelts, and nanotubes of different materials, have significant applications as nanoscale interconnects and active/functional components of electronic and optoelectronic devices, sensors, actuators, nanoelectromechanical systems (NEMS), and energy generation/conversion systems. The thermal and mechanical stabilities of those nanodevices and nanoenabled energy systems are of both theoretical and practical interests. Thermodynamic properties of nanomaterials are different from those of bulk materials. As the size of a solid particle reduces to the nanometer scale, the surface-to-volume ratio increases and the melting temperature may remarkably decrease. The functionality and/or reliability of those nanodevices and nanoenabled energy systems are …

Three-Dimensional Evolution Of Mechanical Percolation In Nanocomposites With Random Microstructures, Bethany Suzanne Fralick

Theses and Dissertations

One mechanism that is expected to play a large role in the enhanced, and sometimes novel, mechanical properties of nanocomposites is the probabilistic formation of percolated or connected microstructures. The majority of the models used to describe mechanical percolation have the functional form of a power law and depend on prior knowledge of a percolation threshold or critical volume fraction. While these models have been fairly accurate predictors of electrical conductivity in composites, they do not take any microstructural mechanisms, other than connectivity, into consideration. Classic mean-field micromechanics models, however, do not capture the variability in effective properties due to …

Structural Health Monitoring Of Composite Laminates Using Piezoelectric And Fiber Optics Sensors, Catalin Roman

Theses and Dissertations

This research proposes a new approach to structural health monitoring (SHM) for composite laminates using piezoelectric wafer active sensors (PWAS) and fiber optic bragg grating sensors (FBG). One major focus of this research was directed towards extending the theory of laminates to composite beams by combining the global matrix method (GMM) with the stiffness transfer matrix method (STMM). The STMM approach, developed by Rokhlin et al (2002), is unconditionally stable and is more computationally efficient than the transfer matrix method (TMM). Starting from theory, we developed different configurations for composite beams and validated the results from the developed analytical method …

Multi-Physicochemical Modeling Of Solid Oxide Fuel Cells And Electrolyzer Cells, Yuanyuan Xie

Theses and Dissertations

Multi-physicochemical models are developed for solid oxide fuel cells and electrolysis cells. The models describe the complicated transport processes of charge (electron/ion) conservation, mass/species conservation, momentum conservation, and energy conservation. Transport processes are coherently coupled with chemical reforming processes, surface elementary reaction processes, as well as electro-oxidation processes of both hydrogen and carbon monoxide. The models are validated with experimental data and utilized for fundamental mechanism studies of SOFCs fueled with different type of fuels, such as hydrogen, hydrocarbon, e.g., methane, H2S, and their mixtures. The fundamental mechanisms associated with syngas generation using electrolysis cell are also extensively investigated using …

Microstructural-Based Modeling Of Electrical Percolation In Polymer Nanocomposites, Neelima Yellepeddi

Theses and Dissertations

Polymer nanocomposites (PNCs) represent a radical alternative to conventional filled polymers or polymer blends. In contrast to conventional composites, where the included phase is on the order of micrometers, PNCs are defined as those that have discrete constituents on the order of a few hundred nanometers. The value of PNCs is not solely based on tailoring mechanical properties, as in traditional composite design and manufacture, but rather on the potential for the design and optimization of multi-functional properties. There is major interest in these polymeric materials embedded with a conductive nanoscale filler. This is due to the possibility of designing …

Modeling And Simulation Study Of A Dynamic Gas Turbine System In A Virtual Test Bed Environment, Eshwarprasad Thirunavukarasu

Theses and Dissertations

Gas Turbine is a complex system and highly non linear in its overall performance. For power generation applications, it is essential to develop a reliable gas turbine model for simulating the impact on electric power generated under various load conditions. This research focuses on development of a dynamic gas turbine model to simulate both single shaft and twin shaft engines. The model is developed on a virtual test bed platform which is an advanced dynamic multidisciplinary simulation environment. The modeling approach starts by developing mathematical models for individual components of gas turbines based on the thermodynamic laws and is coupled …

Boiling And Evaporation On Micro/Nanoengineered Surfaces, Xianming Dai

Theses and Dissertations

Two-phase transport is widely used in energy conversion and storage, energy efficiency and thermal management. Surface roughness and interfacial wettability are two major impact factors for two-phase transport. Micro/nanostructures play important roles in varying the surface roughness and improving interfacial wettability. In this doctoral study, five types of micro/nanoengineered surfaces were developed to systematically study the impacts of interfacial wettability and flow structures on nucleate boiling and capillary evaporation. These surfaces include: 1) superhydrophilic atomic layer deposition (ALD) coatings; 2) partially hydrophobic and partially hydrophilic composite interfaces; 3) micromembrane-enhanced hybrid wicks; 4) superhydrophilic micromembrane-enhnaced hybrid wicks, and 5) functionalized carbon …