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Title: Exploiting internal resonance in MEMS for signal processing applications
Creator: Strachan, Brian Scott
Date: 2017
Collection: Electronic Theses & Dissertations
Description: This research focuses on the development and analysis of predictive modelsfor frequency converters and frequency generators that are based on micro-electromechanical-system(MEMS) technology. In contrast to applications in which nonlinearityis sought to be avoided, frequency conversion and frequency generationnecessarily involve nonlinear processes, and while many existing technologies areavailable for realizing these operations, MEMS technology offers a potentially advantageouscombination of...
Show moreThis research focuses on the development and analysis of predictive modelsfor frequency converters and frequency generators that are based on micro-electromechanical-system(MEMS) technology. In contrast to applications in which nonlinearityis sought to be avoided, frequency conversion and frequency generationnecessarily involve nonlinear processes, and while many existing technologies areavailable for realizing these operations, MEMS technology offers a potentially advantageouscombination of size, power requirements, and noise characteristics.This dissertation describes a series of investigations related to MEMS frequencyconversion and generation, including: (i) an analytical investigation of a class ofpassive multi-stage frequency dividers, (ii) the design and realization of this behaviorin a MEMS device, (iii) the development of a model for nonlinear modalinteractions in closed loop MEMS and (iv) the development of a computationalmethod for optimizing their nonlinear resonant response through shape optimization.Items (ii) and (iii) were carried out in close collaboration with experimentalgroups at the University of California at Santa Barbara and Argonne NationalLabs, respectively. Item (iv) was carried out in collaboration with the topologyoptimization group at the Technical University of Denmark.The subharmonic frequency divider is based on a class of mechanical structureswith nonlinearly coupled high Q vibration modes with sequential 2:1 internal resonances,for which sequential parametric resonances are used to transfer energyfrom a high frequency mode down to lower frequency modes. We analyze thenormal form for this subharmonic resonance cascade and predict the system re-sponse based on system and driving signal parameters. We then show how todesign and experimentally implement this subharmonic cascade in MEMS, andwe demonstrate frequency division by a factor of eight.The frequency generator model is based on a closed loop oscillator in whichthe resonator element has vibration modes with 1:3 frequency ratio and nonlinearintermodal coupling. Experimental observations have shown that the oscillatorphase noise performance is significantly improved when operating in a coupledmode regime, in which a flexural mode is nonlinearly coupled to a torsionalmode. The device is characterized by comparing its measured open loop responseagainst a model based on 1:3 internal resonance, demonstrating good agreement.The closed loop version of the model is analyzed with a focus on how noise sourcesare filtered through the system into phase noise. This model predicts the signifi-cant drop in phase noise observed when operating with internal resonance. Thispredictive model provides a basis for future designs that take full advantage ofthis nonlinear behavior, which has potential for commercialization in the growingarea of MEMS oscillators.Lastly, we describe the development of a computational tool that allows oneto tailor the nonlinear resonant response of mechanical structures using a combinationof normal forms and structural optimization tools. This approach is usedto improve a device's nonlinear modal coupling by nearly an order of magnitude.Such tools will be important for the continuing development of MEMS that utilizenonlinear resonant behavior.In summary, it is shown that internal resonance, in addition to offering interestingdynamic behavior, can be used to improve the performance of signal processingdevices. This work also demonstrates that devices that use internal resonancecan be analyzed with generic dynamic models, thereby providing a basis for understandingfundamental device characteristics and future design development.
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Title: Torque generation during the unsteady expansion process in curved channels of a wave disc engine
Creator: Quispe-Abad, Raul
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "Worldwide demand for power has been growing exponentially, but its production is causing undeniably negative effects; environmental regulations are changing and becoming stricter. The desire for economical but environmentally friendly engines is focusing on toward alternative methods to produce power. "The Wave Disc Engine" (WDE) is a proposed technology to surpass these requirements. The reduction of mechanical parts in the drive train compared with an IC engine and the use of CNG or any...
Show more"Worldwide demand for power has been growing exponentially, but its production is causing undeniably negative effects; environmental regulations are changing and becoming stricter. The desire for economical but environmentally friendly engines is focusing on toward alternative methods to produce power. "The Wave Disc Engine" (WDE) is a proposed technology to surpass these requirements. The reduction of mechanical parts in the drive train compared with an IC engine and the use of CNG or any other renewable fuel gas make this WDE an attractive technology to generate power. This new engine concept is a radial rotor in which the typical processes of an Internal Combustion Engine (Compression, Combustion, and Expansion) are realized. Several prototypes were built between 2011 and 2013. For torque production, the unsteady expansion process of outflowing combusted gases is harnessed. This is a new engine concept with incipient research, investigating the mechanism to generate power under unsteady-state conditions. This research work focuses on determining factors that contribute to produce torque in radial rotor channels under unsteady-state conditions. Computational fluid dynamic numerical simulations and analytical method were employed in this investigation. The study initially focuses on the influence of channel parameters (width, height and length); and concludes that channel length and pressure side area all influence torque generation. Both length and pressure side area combine to raise the efficiency and power generated. Because of the unsteady expansion of the gas, an alternative approach was used to evaluate the performance. The Exergetic efficiency produced results for the channel geometry and conditions tested in the range of 31 to 67%. In addition to that, the approach revealed between 82 to 89% of the exergy, initially contained in the channel, still has the potential to be converted into torque in subsequent stages. In addition, a zero dimensional macroscopic approximate balance equation was derived based on the first law of thermodynamics to calculate the unsteady generated work from the unsteady expansion process. Results show prolonging the duration of unsteady expansion process enhances the isentropic extracted work toward the maximum value. In addition to that, the gas expands more efficiently at lower pressure ratios. The impact on the tangential force by the parameters: beta angle, area of influence, and static pressure on pressure and suction sides of a constant cross-section channel, are investigated. The first two parameters change inversely but when combined show similar values at each pressure and suction wall location. Also, most of the generated torque was found in zones near the channel outlet. Furthermore, the torque generation composed of the action of two effects: the change of the angular momentum of the fluid within channel and the outflow rate of the angular momentum at the channel outlet is investigated. These two components are referred as unsteady and steady effects respectively based on the mechanism to produce torque. Results show the torque production benefits when the channel opens quickly. The increase of rotational velocity approximates the quick opening. Unsteady effects produce a significant part of the generated torque and the steady effect can be small at high speed."--Pages ii-iii.
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Title: Gas-phase synthesis of semiconductor nanocrystals and its applications
Creator: Rajib, Md, 1983-
Date: 2016
Collection: Electronic Theses & Dissertations
Description: Luminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties...
Show moreLuminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties owing to their size as compared to their bulk counterparts. Here we describe the use of plasmas in synthesis, modification, and deposition of semiconductor nanomaterials for luminescence applications.Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications in several areas. To date, however, luminescent silicon nanocrystals (NCs) have been used exclusively in traditional rigid devices. For the field to advance towards new and versatile applications for nanocrystal-based devices, there is a need to investigate whether these NCs can be used in flexible and stretchable devices. We show how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made of polydimethylsiloxane (PDMS). Synthesis of these NCs was performed in a nonthermal, low-pressure gas phase plasma reactor. To our knowledge, this is the first demonstration of direct deposition of NCs onto stretchable substrates.Additionally, in order to prevent oxidation and enhance the luminescence properties, a silicon nitride shell was grown around Si NCs. We have demonstrated surface nitridation of Si NCs in a single step process using non‒thermal plasma in several schemes including a novel dual-plasma synthesis/shell growth process. These coated NCs exhibit SiNx shells with composition depending on process parameters. While measurements including photoluminescence (PL), surface analysis, and defect identification indicate the shell is protective against oxidation compared to Si NCs without any shell growth.Gallium Nitride (GaN) is one of the most well-known semiconductor material and the industry standard for fabricating LEDs. The problem is that epitaxial growth of high-quality GaN requires costly substrates (e.g. sapphire), high temperatures, and long processing times. Synthesizing freestanding NCs of GaN, on the other hand, could enable these novel device morphologies, as the NCs could be incorporated into devices without the requirements imposed by epitaxial GaN growth. Synthesis of GaN NCs was performed using a fully gas-phase process. Different sizes of crystalline GaN nanoparticles were produced indicating versatility of this gas-phase process. Elemental analysis using X-ray photoelectron spectroscopy (XPS) indicated a possible nitrogen deficiency in the NCs; addition of secondary plasma for surface treatment indicates improving stoichiometric ratio and points towards a unique method for creating high-quality GaN NCs with ultimate alloying and doping for full-spectrum luminescence.
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Title: Control of hybrid dynamics with application to a hopping robot
Creator: Mathis, Frank Benton
Date: 2016
Collection: Electronic Theses & Dissertations
Description: "Control of dynamic motion is an important subject of study in robotics as it is desirable for robots to have a specific motion pattern rather then moving to a set point. The motions of robots also involve changing dynamic behaviors due to interaction with the environment, such as during contact, and this leads to hybrid system dynamics. A popular example of a hybrid dynamical system is a legged robot; the hybrid dynamics is due to the periodic switching of swing and stance legs and impulsive...
Show more"Control of dynamic motion is an important subject of study in robotics as it is desirable for robots to have a specific motion pattern rather then moving to a set point. The motions of robots also involve changing dynamic behaviors due to interaction with the environment, such as during contact, and this leads to hybrid system dynamics. A popular example of a hybrid dynamical system is a legged robot; the hybrid dynamics is due to the periodic switching of swing and stance legs and impulsive dynamics due to ground contacts. Legged robots require control of a dynamic trajectory defined by the walking gait or running motion. For legged robots, the spring loaded inverted pendulum (SLIP) model is commonly used to describe the dynamic motion in a simplified manner. The SLIP model has also been used for control of hopping robots and a fundamental limitation of the model is that it fails to account for impact with the ground; this is due to its single degree-of-freedom in the vertical direction. We investigate the control of a hopping robot starting from a more general two-mass model and then expand the theory to planar multi-link robot systems. The investigation involves two ground contact models, rigid and elastic, for the objective of apex height control. In the rigid case, the ground is assumed to provide an impulsive force to the hopping robot resulting in an inelastic collision. A hybrid control strategy is designed to deal with the hybrid dynamical system: a continuous controller based on partial feedback linearization is used in conjunction with a discrete controller that updates a control parameter at each hop to achieve the control objective. In the elastic case, the ground acts as a massless spring, which deflects as the robot exerts a force upon contact. In this case, we show that a continuous controller based on the backstepping algorithm can ensure asymptotic convergence to the desired apex height. Several robot configurations are considered, and for each configuration the complete hybrid dynamics is taken into account while designing the controller. The controllers compensate for the impulsive dynamics as well as higher order dynamics that are ignored in simplified models such as the SLIP model. Experimental validation of apex height control of a two-mass hopping robot on a rigid foundation is provided"--Pages ii-iii.
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Title: A robust crash simulation model for composite structures
Creator: Shi, Danghe
Date: 2016
Collection: Electronic Theses & Dissertations
Description: Fiber reinforced composites are widely used in aerospace, automotive and other industries due to their high stiffness & strength-to-weight ratio, corrosion resistant and energy absorption ability. The use of composites in primary energy absorbing components in vehicles, however, is very limited. The lack of robust and accurate models for the prediction of crashworthiness performance of composite structures is a critical factor. The capability of crash simulations is often examined with axial...
Show moreFiber reinforced composites are widely used in aerospace, automotive and other industries due to their high stiffness & strength-to-weight ratio, corrosion resistant and energy absorption ability. The use of composites in primary energy absorbing components in vehicles, however, is very limited. The lack of robust and accurate models for the prediction of crashworthiness performance of composite structures is a critical factor. The capability of crash simulations is often examined with axial impact of tubes, a benchmark problem. Among the large amount of published works on modeling composite tubes under axial impact, very few were able to predict both the failure morphologies and force-displacement responses of a crushing tube, especially for the ones without a plug initiator at the crash front. One of the problems is related to the limitations of material constitutive models. The existing composite material models used in crash simulations generally contain a few non-measurable parameters while ignoring the irreversible strains which can be important to the prediction of energy absorption. The other problem is related to the robustness of the finite element (FE) models. Traditional elements tend to have instability issues under in-plane compression.In order to solve these problems, this study proposes a new crash model which composes of an Enhanced Continuum Damage Mechanics (ECDM) model and a Shell-Beam (SB) element modeling method. The ECDM model consists of a pre-failure sub-model, based on the modified Ladevèze model, and a post-failure sub-model. It considers both the matrix plasticity and irreversible strains due to damage. The SB element method enhances the shell element with real out-of-plane properties by introducing beam elements in the out-of-plane direction. As a result, the SB element is stable under in-plane compression while retaining the efficiency of the shells. The ECDM has been implemented in LS-DYNA as a user-defined material model.To evaluate the predictive capability of this new crash model, simulations are carried out for both quasi-static tests and dynamic tube crash tests of 2D triaxial braided composites (2D3A). For dynamic tube crash tests, two different groups of tests are done on composite tubes, with and without a plug initiator. The results show that the ECDM model is able to simulate the force and energy responses as well as the failure morphologies more accurately than a widely used CDM model available in LS-DYNA. On the other hand, the SB element method allows one to capture most of the damage modes of a composite tube under axial crash without the numerical difficulties experienced by using traditional elements, like negative element volume, infinite small timesteps, and instability. Both ECDM model and SB element method are also robust enough to be used on different geometries.To have a better understanding of ECDM model and shell-beam method, a sensitivity study is carried out at the end of this study for key model parameters, such as the tiebreak contact strength, friction coefficient, element deletion strain, etc.
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Title: Numerical simulations for performance enhancement of a radial, pressure wave driven, internal combustion engine
Creator: Kiran, Rohitashwa
Date: 2013
Collection: Electronic Theses & Dissertations
Description: The Wave Disk Engine is a new engine concept which employs pressure wave compression and expansion, constant volume combustion, and power extraction within a compact rotating disk. It is a logical next step in the advancement of internal combustion wave rotor technology. Such devices achieve compression of a combustible mixture by the sudden closing of a port and power extraction when a port opens. The timing of port opening and closing is determined by the time required for compression and...
Show moreThe Wave Disk Engine is a new engine concept which employs pressure wave compression and expansion, constant volume combustion, and power extraction within a compact rotating disk. It is a logical next step in the advancement of internal combustion wave rotor technology. Such devices achieve compression of a combustible mixture by the sudden closing of a port and power extraction when a port opens. The timing of port opening and closing is determined by the time required for compression and expansion waves to travel along the length of the channel. Most of the research in this field has been directed at finding the correct port timings purely on the basis of fluid mechanics. However combustion inside these devices has not been studied in a thorough manner either numerically or experimentally. The first part of this work discusses numerical investigations attempting to understand the combustion process in the presence of a periodic flow induced by the opening and closing of ports. Numerical evaluations are provided for the detailed flame shape for simplified chemistry and a simulation using the detailed San Diego mechanism. Other quantities examined are vorticity, pressure fluctuations, mass consumption rate, flame surface area and the influences of adiabatic and non-adiabatic channel walls. The focus of the study is on quantities that influence overall burning rate and completeness of combustion.The second part of this work deals with the introduction of certain design features to the Wave Disk Engine which can help in increasing the power extraction and overall efficiency of the device. These include - reinjection of combusted gas into fresh combustible mixture, a second row of turbine blades outside the wave disk, and an external combustion chamber. The overall thermodynamic efficiency of this device, which references the Humphrey thermodynamic cycle, increases with the increased pressure inside the combustion channel prior to combustion. One possible and sustainable way of achieving pre-compression in a combustion channel is to re-inject combusted gas from the previous cycle, before it is expanded. Computational fluid dynamic simulations are run for different angular speeds of the engine and widths of the re-injection passage. A balance is sought between loss of mass and enthalpy in a high pressure combustion channel and the gain in pressure and enthalpy in the low pressure channel, which would maximize overall cycle efficiency. A Wave Disk Engine equipped with a reinjection passage as well as a second row of turbine blades is provides the highest thermodynamic efficiency in this study. Another Wave Disk Engine design is proposed which addresses the problem of seizing by using two discs made of ceramic stacked on top of each other. One disc serves as a combustion chamber and the other to compress fuel-air mixture and generate power.
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Title: Multiscale modeling of polymer nanocomposites
Creator: Sheidaei, Azadeh
Date: 2015
Collection: Electronic Theses & Dissertations
Description: In recent years, polymer nano-composites (PNCs) have increasingly gained more attention due to their improved mechanical, barrier, thermal, optical, electrical and biodegradable properties in comparison with the conventional micro-composites or pristine polymer. With a modest addition of nanoparticles (usually less than 5wt. %), PNCs offer a wide range of improvements in moduli, strength, heat resistance, biodegradability, as well as decrease in gas permeability and flammability. Although...
Show moreIn recent years, polymer nano-composites (PNCs) have increasingly gained more attention due to their improved mechanical, barrier, thermal, optical, electrical and biodegradable properties in comparison with the conventional micro-composites or pristine polymer. With a modest addition of nanoparticles (usually less than 5wt. %), PNCs offer a wide range of improvements in moduli, strength, heat resistance, biodegradability, as well as decrease in gas permeability and flammability. Although PNCs offer enormous opportunities to design novel material systems, development of an effective numerical modeling approach to predict their properties based on their complex multi-phase and multiscale structure is still at an early stage. Developing a computational framework to predict the mechanical properties of PNC is the focus of this dissertation. A computational framework has been developed to predict mechanical properties of polymer nano-composites. In chapter 1, a microstructure inspired material model has been developed based on statistical technique and this technique has been used to reconstruct the microstructure of Halloysite nanotube (HNT) polypropylene composite. This technique also has been used to reconstruct exfoliated Graphene nanoplatelet (xGnP) polymer composite. The model was able to successfully predict the material behavior obtained from experiment. Chapter 2 is the summary of the experimental work to support the numerical work. First, different processing techniques to make the polymer nanocomposites have been reviewed. Among them, melt extrusion followed by injection molding was used to manufacture high density polyethylene (HDPE) – xGnP nanocomposties. Scanning electron microscopy (SEM) also was performed to determine particle size and distribution and to examine fracture surfaces. Particle size was measured from these images and has been used for calculating the probability density function for GNPs in chapter 1. A series of nanoindentation tests have been conducted to reveal the spatial variation of the superstructure developed along and across the flow direction of injection-molded HDPE/GNP.The uniaxial tensile test and shear test have been conducted on HDPE and xGnP/HDPE specimens. The stress-strain curves for HDPE obtained from these experiments have been used in chapter 5 to calibrate the modified Gurson–Tvergaard–Needleman to capture the damage progression in HDPE. In chapter 3, the 3D microstructure model developed in chapter 1 was incorporated in a damage modeling problem in nanocomposite where damage initiation has been modeled using cohesive-zone model. There is a significant difference between the properties of inclusion and the host polymer in polymer nanocomposite, which leads to the damage evolution during deformation due to a huge stress concentration between nanofiller and polymer. The finite element model of progressive debonding in nano-reinforced composite has been proposed based on the cohesive-zone model of the interface. In order to model cohesive-zone, a cohesive zone traction displacement relation is needed. This curve may be obtained either through a fiber pullout experiment or by simulating the test using molecular dynamics. In the case of nano-fillers, conducting fiber pullout test is very difficult and result is often not reproducible. In chapter 4, molecular dynamics simulation of polymer nanocomposite has been performed. One of the goals was to extract the load-displacement curves of graphene/HDPE pullout test and obtain cohesive zone parameters in chapter 3. Finally, in chapter 5, a damage model of HDPE/GNP nanocomposite has been developed based on matrix cracking and fiber debonding. This 3D microstructure model was incorporated in a damage modeling problem in nanocomposite where damage initiation and damage progression have been modeled using cohesive-zone and modified Gurson-Tvergaard-Needleman (GTN) material models.
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Title: Permeability of fiber reinforcements for liquid composite molding : sequential multi-scale investigations into numerical flow modeling on the micro- and meso-scale
Creator: Luchini, Timothy John Franklin
Date: 2015
Collection: Electronic Theses & Dissertations
Description: Composites are complex material mixtures, known to have high amounts of variability, with unique properties at the micro-, meso-, and macro-scales. In the context of advanced textile composite reinforcements, micro-scale refers to aligned fibers and toughening agents in a disordered arrangement; meso-scale is the woven, braided, or stitched fabric geometry (which compacts to various volume fractions); and macro-scale is the component or sub-component being produced for a mechanical...
Show moreComposites are complex material mixtures, known to have high amounts of variability, with unique properties at the micro-, meso-, and macro-scales. In the context of advanced textile composite reinforcements, micro-scale refers to aligned fibers and toughening agents in a disordered arrangement; meso-scale is the woven, braided, or stitched fabric geometry (which compacts to various volume fractions); and macro-scale is the component or sub-component being produced for a mechanical application. The Darcy-based permeability is an important parameter for modeling and understanding the flow profile and fill times for liquid composite molding. Permeability of composite materials can vary widely from the micro- to macro-scales. For example, geometric factors like compaction and ply layup affect the component permeability at the meso- and macro-scales. On the micro-scale the permeability will be affected by the packing arrangement of the fibers and fiber volume fraction. On any scale, simplifications to the geometry can be made to treat the fiber reinforcement as a porous media. Permeability has been widely studied in both experimental and analytical frameworks, but less attention has focused on the ability of numerical tools to predict the permeability of reinforced composite materials. This work aims at (1) predicting permeability at various scales of interest and (2) developing a sequential, multi-scale, numerical modeling approach on the micro- and meso-scales. First, a micro-scale modeling approach is developed, including a geometry generation tool and a fluids-based numerical permeability solver. This micro-scale model included all physical fibers and derived the empirical permeability constant directly though numerical simulation. This numerical approach was compared with literature results for perfect packing arrangements, and the results were shown to be comparable with previous work. The numerical simulations described here also extended these previous investigations by including the ability to study binary mixtures of commingled fibers, random packing, particulate loadings, and permeability variation at a single volume fraction as a function of the mean inter-fiber spacing. Extending this approach from the micro-scale to the meso-scale creates an opportunity to quantify the effect of dual-scale porous media. More specifically, direct numerical simulations of carbon fiber reinforcement on the micro-scale were compared to measurements of unidirectional carbon fabrics on the meso-scale. The results showed a quantifiable effect of dual-scale porous media in composite processing, with generally higher permeability on the meso-scale. Next, a three-dimensional meso-scale analysis of a plain weave composite fabric was performed using the homogenized micro-scale permeability. Comparisons were made between the numerical modeling approaches developed in this dissertation with the available permeability measurement techniques for validation. The meso-scale permeability calculations compared well with experimental permeability measurements. The effect of fabric variability is seen in all scales of interest. Finally, this work included a meso-scale, two-phase, transient simulation to investigate tow saturation and the formation of meso-scale voids. The results qualitatively show the nature of the advancing fluid front and the lagging tow saturation, which is seen though experimental analysis.
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Title: Design considerations and estimated on-vehicle performance for a compression-couple based thermoelectric generator
Creator: Mansouri Boroujeni, Nariman
Date: 2015
Collection: Electronic Theses & Dissertations
Description: Approximately 55% percent of the energy produced from conventional vehicle resources is lost in the form of heat. An efficient waste heat recovery process will undoubtedly lead to improved fuel efficiency, reduced greenhouse gas emissions and increased profit. Thermoelectric generators (TEGs) are one of the most viable waste heat recovery approaches that are being widely studied among energy-intensive industries which focus on the ways to convert waste heat energy to electrical energy. With...
Show moreApproximately 55% percent of the energy produced from conventional vehicle resources is lost in the form of heat. An efficient waste heat recovery process will undoubtedly lead to improved fuel efficiency, reduced greenhouse gas emissions and increased profit. Thermoelectric generators (TEGs) are one of the most viable waste heat recovery approaches that are being widely studied among energy-intensive industries which focus on the ways to convert waste heat energy to electrical energy. With the rising cost of fuel and increasing demand for clean energy, solid-state thermoelectric (TE) devices are good candidates to reduce fuel consumption and CO2 emissions in an automobile. Although they are reliable energy converters, there are several barriers that have limited their implementation into wide market acceptance for automotive applications. These barriers include: the unsuitability of conventional thermoelectric materials for the automotive waste heat recovery temperature range; the rarity and toxicity of some otherwise suitable materials; and the limited ability to mass-manufacture thermoelectric devices from certain materials. However, skutterudite is one class of material that has demonstrated significant promise in the transportation waste heat recovery temperature domain. These materials have little toxicity, relatively abundant, and have been studied and developed by NASA-JPL and others for the past 20 years.The converted electrical energy can be used to recharge batteries, run auxiliary electrical accessories, support heating system, and etc. However, durability and reliability of the thermoelectric generators are the most significant concerns in the product development process. Cracking of the skutterudite materials at hot-side interface is found to be a major failure mechanism of thermoelectric generators under thermal cyclic loading. Cracking affects not only the structural integrity but also the energy conversion and overall performance of the system. In this project, cracking of thermoelectric material as observed in performance testing is analyzed using numerical simulations and analytic experiments. With the help of finite element analysis, the detailed distribution of stress, strain, and temperature are obtained for each design. Finite element based simulations show the tensile stresses as the main reason causing radial and circumferential cracks in the skutterudite. For thermoelectric generator design, loading conditions, closed-form analytical solutions of stress/strain distributions are derived and scenarios with minimum tensile stresses are sought. All these approaches yield a minimum stress/strain necessary to produce any cracks. Finally, based on FE and computational fluid dynamic (CFD) analysis, strategies in tensile stress reduction and failure prevention are proposed followed by the reasons to change the thermoelectric couple design for having a reliable thermoelectric generator.Using a modified compression couple technology, a 15-watt thermoelectric generator prototype was designed, built and tested. Experimental results of the TEG are presented. This prototype was analyzed using 1-D engine simulation and computational fluid dynamics (CFD), and the resulting analysis is presented. In a model configuration utilizing eight of these 15-watt TEGs, each having a 4% conversion efficiency, an estimated 136 watts of electricity could be produced at an operating point of 2000 RPM and 3 bar engine load in a 4.7L V6 gasoline engine.
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Title: A kinematics-based model of hand function for clinical evaluation and design of handheld objects
Creator: Leitkam, Samuel Thomas
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Hand function is quantified in different ways for clinical evaluation and object design. It is measured in the clinical environment to evaluate changes in function and levels of function with respect to the population. In design, it is used to understand what healthy hands can do so that objects can be made to fit the abilities of users. However, no hand function quantification method is currently applied to both evaluation and design, allowing for design of objects for individuals with...
Show moreHand function is quantified in different ways for clinical evaluation and object design. It is measured in the clinical environment to evaluate changes in function and levels of function with respect to the population. In design, it is used to understand what healthy hands can do so that objects can be made to fit the abilities of users. However, no hand function quantification method is currently applied to both evaluation and design, allowing for design of objects for individuals with reduced functional abilities in their hands.The goals of the research were to: 1) develop a kinematics-based model of the 3D reachable space of the fingers of the hand, weighted by objective measures of functional ability; 2) assess the model's ability to evaluate levels of function between individuals with varying levels of hand function; and 3) demonstrate that the model could be applied to a design scenario to assist in designing handheld objects for groups of individuals, specifically groups with reduced functional abilities. These goals were addressed by three different research studies. The first study presented the mathematical development of the weighted fingertip space (WFS) model and an initial evaluation of the model as applied to a theoretical 50th percentile male hand and nine healthy individuals. The WFS model transformed hand dimensions and finger joint ranges of motion into a three-dimensional representation of all of the points in space reachable by the fingertips. The reachable points were then weighted based on the number of ways each point could be reached, the range of fingertip pad orientations possible at each point, and the range of force application directions that could be applied at each point. The results showed that the model was capable of calculating and presenting the weighted functional space, and the theoretical 50th percentile male model showed similarities in size, shape, and weighting patterns to the models developed from the individuals with similar sized hands. In addition, the models all showed distinct spatial patterns for each of the three weighting parameters. From this, it was shown that the WFS model could have potential application in both evaluation of function and design.The second study examined the differences between WFS models of healthy and arthritic individuals to assess the model's ability to evaluate function for clinical purposes. Hand dimensions and ranges of motion were measured for 22 healthy and 21 arthritic individuals, and WFS models were calculated for each participant. In addition, the models from the individuals were combined to evaluate whether a universally reachable space existed for each group. The results showed that the model was capable of differentiating levels of function as the arthritic group showed lower functional values than the healthy group. Further, the group models showed that a universally reachable space existed for the healthy group, but not for the entire arthritic group. However, the arthritic group's most reachable spaces overlapped with the universally reachable space of the healthy group.The third study showed the WFS model's ability to aid in design by demonstrating that the model's 3D representation of functional weighting values could be mapped to the surface a 3D modeled handheld object and interpreted for a given task. The models developed in the second study were all mapped to the surfaces of cylinders of varying size representative of a handheld device, an auto-injector. The mappings of the model to the cylinders were used to evaluate the diameter of cylinder that best matched the abilities of the individuals. It was shown that for both the healthy and arthritic groups, the WFS models mapped the highest levels of functional weightings to the 40 mm cylinder diameter. From this research, it was shown that the WFS model can be used to evaluate handheld object designs for groups of individuals based on objective hand function quantifications.
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Title: Topology optimization applied to design of solid oxide fuel cells
Creator: Song, Xiankai
Date: 2014
Collection: Electronic Theses & Dissertations
Description: A topology optimization method is used to identify optimal designs of the cathode microstructure and the anode support in a solid oxide fuel cell (SOFC). Two dimensional and three dimensional models are considered. A 2D topology optimization model is developed to minimize the cathode resistance. A simplified analysis model is used in computations. Results highlight the importance of the cathode geometry in the performance. Optimal geometric features are found to depend on the material...
Show moreA topology optimization method is used to identify optimal designs of the cathode microstructure and the anode support in a solid oxide fuel cell (SOFC). Two dimensional and three dimensional models are considered. A 2D topology optimization model is developed to minimize the cathode resistance. A simplified analysis model is used in computations. Results highlight the importance of the cathode geometry in the performance. Optimal geometric features are found to depend on the material properties and various geometric parameters.To improve upon the accuracy available from a purely 2D model, a 3D finite element model is established to make an accurate prediction of the cathode resistance. A detailed 3D microstructure is reconstructed from images obtained using the 3D focused ion beam-scanning electron microscopy. A 3D topology optimization formulation is set up to minimize cathode resistance. The effect of the material properties on the geometric features is investigated. Improvements up to 35% are achieved by properly organizing the cathode microstructure.The thermal stress problem of the anode support in the SOFC stacks is also of great interest. Fuel flow, heat transfer, thermo-mechanical and electrochemical processes are considered in a coupled model. A Weibull distribution evaluating the probability of failure is used as a measure of the strength of the anode. A new material model is developed aiming at the topology optimization of the anode strength. Optimal designs for two types of objective functions, including minimum thermal compliance and minimum probability of failure, are obtained. It is observed that the designs obtained using the two objective functions can improve the performance for 10%.
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Title: Simultaneous flow visualization and unsteady-surface-pressure measurements in normally and obliquely laminar impinging jets
Creator: Al-Aweni, Malek Omar
Date: 2013
Collection: Electronic Theses & Dissertations
Description: Impinging jets are important in many engineering applications, such as heating, cooling, drying and Short Takeoff and Landing (STOL) aircrafts, as well as in understanding some of nature's phenomena, such as microbursts. There are numerous studies on the heat transfer from the surface upon which the jet impinges, but comparatively very few investigations of the space-time characteristics of the pressure fluctuations acting on the impingement wall. Moreover, the bulk of the latter...
Show moreImpinging jets are important in many engineering applications, such as heating, cooling, drying and Short Takeoff and Landing (STOL) aircrafts, as well as in understanding some of nature's phenomena, such as microbursts. There are numerous studies on the heat transfer from the surface upon which the jet impinges, but comparatively very few investigations of the space-time characteristics of the pressure fluctuations acting on the impingement wall. Moreover, the bulk of the latter investigations lack concurrent flow-field information, and therefore their conclusions regarding the pressure generation mechanisms remain largely hypothetical. The current study investigates the impinging-jet flow structures and their relation to the wall-pressure signature employing simultaneous unsteady-surface-pressure measurements, using a microphone array, and time-resolved flow visualization, using the smoke-wire technique, in an axisymmetric jet in normal and oblique impingement. The investigation is conducted at a jet Reynolds number based on diameter of 7334 for separations between the jet exit and the impingement plate ranging from two to four jet diameters, at normal and 30o oblique impingement angles. Spectral analysis of the surface pressure fluctuations show that the flow above the wall contains higher Strouhal numbers when the plate is placed closer to the jet exit. The flow structures and mechanisms responsible for generating the pressure fluctuations at these Strouhal numbers are revealed using the simultaneous pressure and flow visualization information. It is found that within the wall-jet region, where the highest pressure fluctuations are observed, the pressure fluctuations are predominantly influenced by the advection and evolution of the jet vortices and their interaction with each other and with the wall. These vortices are observed to exhibit one of two scenarios within the wall jet zone: to pass without mutual interaction, or to merge as they travel above the wall. In the passage scenario, as the vortex travels above the wall, it very often forms a secondary vortex, via interaction with the wall. This interaction leads to the generation of a strong negative pressure spike at the radial locations where the pressure fluctuation is large. A qualitatively similar signature is also found in the vortex merging scenario, although in this case the pressure spike is substantially stronger and secondary-vortex formation could not be seen in the smoke visualization. In order to study this phenomenon in more details, numerical computations of related model problems are carried out using Ansys Fluent. These problems involve the evolution of a single and dual axisymmetric vortex rings that interact with a flat wall. The resulting databases are analyzed by studying the volumetric distribution of the wall-pressure sources and their wall-pressure imprint using Green's function solution of Poisson's equation for pressure. The results reveal pressure signatures that are qualitatively similar to those observed experimentally in the impinging jet. The pressure-source analysis reveals the mechanisms leading to these signatures and the associated contribution of the individual flow features.
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Title: Reaction-based modeling and control of an electrically boosted diesel engine
Creator: Men, Yifan
Date: 2019
Collection: Electronic Theses & Dissertations
Description: This dissertation presents the reaction-based modeling of diesel combustion and model-based control of diesel engine air path.The dissertation first presents a control-oriented reaction-based diesel combustion model that predicts the time-based rate of combustion, in-cylinder gas temperature and pressure over one engine cycle. The model, based on the assumption of a homogeneous thermodynamic combustion process, utilizes a two-step chemical reaction mechanism that consists of six species:...
Show moreThis dissertation presents the reaction-based modeling of diesel combustion and model-based control of diesel engine air path.The dissertation first presents a control-oriented reaction-based diesel combustion model that predicts the time-based rate of combustion, in-cylinder gas temperature and pressure over one engine cycle. The model, based on the assumption of a homogeneous thermodynamic combustion process, utilizes a two-step chemical reaction mechanism that consists of six species: diesel fuel (C10.8H18.7), oxygen (O2), carbon dioxide (CO2), water (H2O), nitrogen (N2), and carbon monoxide (CO). The temperature variation rate is calculated based on the rate of change of species concentrations, and the heat loss correlation is also used to study the model performance. The accuracy of the model is evaluated using the test data from a production GM 6.6 L, 8-cylinder, turbocharged engine. The model is calibrated over large engine speed and load range as well as different injection timings and exhaust gas recirculation (EGR) rates by solving the optimization problem. The calibrated reaction-based model accurately predicts the indicated mean effective pressure, while keeping the errors of in-cylinder pressure and temperature small, and at the same time, significantly reduces the calibration effort, especially when the engine is operated under multiple fuel injection operations, comparing to Wiebe-based combustion models. The calibrated model parameters have a strong correlation to engine speed, load and injection timings, and as a result, a universal parameter calibration structure is proposed for entire operational conditions.The second part of the dissertation is to obtain a parametric understanding of diesel combustion by developing a physics-based model that is able to predict the combustion metrics, such as in-cylinder pressure, burn rate, and indicated mean effective pressure (IMEP) accurately, over a wide range of operating conditions, especially with multiple injections. In the proposed model, it is assumed that the engine cylinder is divided into three zones: a fuel zone, a reaction zone, and an unmixed zone. The formulation of reaction and unmixed zones is based on the reaction-based modeling methodology, where the interaction between them is governed by Fick's law of diffusion. The fuel zone is formulated as a virtual zone, which only accounts for mass and heat transfer associated with fuel injection and evaporation. The model is validated using test data under different speed and load conditions, with multiple fuel injections and EGR. It is shown that the three-zone model outperformed the single-zone model in in-cylinder pressure prediction and calibration effort with a mild penalty in computational time. One set of calibration parameters are used for all engine operating conditions.The third part of the dissertation is modeling and control of engine air path with an electrically assisted boosting system. A physics-based control-oriented engine air path model with electrical assistance has been developed. The model is validated with steady-state engine test data and standard driving cycle data. Through one-dimensional simulation, it is found that the electrically assisted boosting system is able to improve engine performance under both steady-state and transient conditions. A model-based controller has been developed for the electric booster (eBoost) and bypass valve to improve the transient performance of engine load response. Experiments have been performed on a Ford 6.7 L, 8-cylinder, turbocharged diesel engine equipped with a prototype eBoost and a standard EGR valve as the bypass valve. Steady-state test results have shown that eBoost is capable of improving engine efficiency by reducing pumping loss, due to reduced turbine speed when eBoost is providing additional boost energy. In the transient process, eBoost is able to significantly reduce the response time of boost pressure tracking, as validated by load step tests.
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Title: Microscale medium-to-high-temperature reactors via modified binder jet printing processes and pitch control in nanosphere patterns via soft lithography
Creator: Huang, Xiaolu
Date: 2019
Collection: Electronic Theses & Dissertations
Description: A conventional approach to making miniature or microscale reactor components (e.g., heat exchangers, microreactors, separators, etc.) relies on silicon as a base material and MEMS fabrication as manufacturing processes. These Si-based microfluidic devices, however, often fail in applications involving medium-to-high-temperature operations due to lack of robust fluidic interconnects and a high-yield bonding process required to make those devices. Here we explore additive manufacturing (AM),...
Show moreA conventional approach to making miniature or microscale reactor components (e.g., heat exchangers, microreactors, separators, etc.) relies on silicon as a base material and MEMS fabrication as manufacturing processes. These Si-based microfluidic devices, however, often fail in applications involving medium-to-high-temperature operations due to lack of robust fluidic interconnects and a high-yield bonding process required to make those devices. Here we explore additive manufacturing (AM), also known as metal 3D printing, as an alternative platform to produce small scale microfluidic devices that can operate at temperature much higher than what polymers can withstand. Binder jet printing (BJP), is utilized to make stainless steel (SS) preconcentrators (PCs) with submillimeter internal features. Small-scale PCs can increase the concentration of gaseous analytes or serve as an inline injector for micro gas chromatography system (micro-GC) or portable gas sensor applications. Normally, parts printed by BJP are highly porous and thus unsuitable as fluidic components due to leaks. By adding to SS316 powder sintering additives such as boron nitride (BN), which reduces the liquid temperature, we produce near full-density SS PCs at sintering temperatures much lower than the SS melting temperature and importantly without any measurable shape distortion. Next, we leverage high initial porosity and decoupling of printing and sintering in BJP to fabricate 3D-printed heterogeneous metal/ceramic structures that are functionally graded. Functionally-graded materials (FGMs) are particularly challenging to produce in AM because of the material and processing incompatibilities caused by the thermal shrinkage/expansion mismatch and residual stress issues. We introduce a selective-reactive sintering (SRS) process to locally tune the electrical properties of BJP-derived SS parts. The SRS process utilizes reactive gaseous environments such as oxygen during sintering and partially converts metal powders to more resistive metal oxides. The combination of BJP and SRS allows the portion of the resulting structures to possess much higher electrical resistance than the other regions, facilitating efficient electrothermal conversion for heat exchanger or reactor applications. Moreover, the heterogeneous nature of the metal/metal oxide structures significantly increases the temperature coefficient of resistance (TCR) compared to that of the raw metal. Large TCR values of the heterogeneous FGM structure makes it highly sensitive to the temperature variation, i.e., useful as resistance-temperature detectors (RTD) or anemometer-like flow sensors at medium-to-high temperatures. The second part of the dissertation is to address the intrinsic limitation of nanosphere lithography (NSL). NSL is known as one of the most inexpensive and widespread nanopatterning approaches, and in conjunction with metal-assisted chemical etching (MACE), can create an array of vertically-aligned silicon nanowires (VA-SiNWs) for various applications including highly-sensitive gas detectors and Li-ion battery anodes. However, VA-SiNWs obtained from NSL and MACE are limited in their size and spacing because the array pitch and wire diameter are inherently linked to the original nanosphere size. Here, we present deformable soft lithography using controlled deformation of elastomeric substrates and subsequent contact printing transfer to systematically control the lattice spacing and arrangements of the nanosphere array. The unique aspect of our approach is to utilize a custom-made radial stretching apparatus that allows the nanospheres to be stretched without disrupting original hexagonal arrangements over large areas. This is different from the patterns obtained from the more conventional uniaxial or biaxial stretching method whose anisotropic nature breaks the hexagonal symmetry.
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Title: Fabrication and assembly of one-dimensional semiconductor nanostructures and their application to multi-functional devices
Creator: Zhang, Yaozhong
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "One-dimensional (1D) semiconducting nanostructures have been extensively studied in the past few decades due to their excellent electrical, chemical and optical properties, which enable remarkable performance in various applications such as electronic/optoelectronic devices, chemical/biological sensors and energy harvesting. Since water pollution becomes as one of the most challenging global issues, photocatalytic degradation has received considerable attentions as an efficient water...
Show more"One-dimensional (1D) semiconducting nanostructures have been extensively studied in the past few decades due to their excellent electrical, chemical and optical properties, which enable remarkable performance in various applications such as electronic/optoelectronic devices, chemical/biological sensors and energy harvesting. Since water pollution becomes as one of the most challenging global issues, photocatalytic degradation has received considerable attentions as an efficient water treatment technology with regard to removing organic contaminants. Upon receiving UV or sunlight irradiation with energy higher than their bandgap, semiconducting materials generate charge carriers such as electrons and holes that react with water and produce reactive species for decomposition. TiO2 and ZnO are the most widely used photocatalysts because of their higher degradability and lower production cost. Especially, TiO2 and ZnO nanostructures exhibit better degradability thanks to their low recombination of charge carriers and large active surface areas. However, the challenges like low utilization of sunlight (mainly responsive to UV light) and non-recyclability limit their large-scale use as photocatalysts. In this work, we tackle these limitations by developing a new immobilized photocatalytic system to improve their recyclability and investigating a novel semiconductor-semiconductor heterogeneous material to enhance their optical response in the visible region. First, ZnO nanowires (NWs) have been synthesized using a hydrothermal process and hybridized with silicon nanocrystals (SiNCs). This heterojunction lowers the ZnO bandgap (more active under visible light) and exhibits superior photodegradation performance under the visible and white light conditions compared to original ZnO NW photocatalysts. Second, we have developed a novel fabrication technique to create a vertically-aligned ZnO NW array on a polymer substrate with strong adhesion. The proposed two-step fabrication process allows the part of NWs to be embedded into the polymer matrix, securing the nanomaterials for harsh operating environments. A ZnO-NW/Polydimethylsiloxane (PDMS) film presents the unique immobilized photocatalytic system that can float on the water surface, targeting buoyant pollutants. In particular, crude oil has been used a model pollutant for degradation experiment. A strong adhesion of ZnO NWs to the polymer substrate also enables two new implementations of the photocatalytic system including the application with high shear stresses and piezoelectrocalysis. The latter application is particularly interesting as organic pollutants were degraded via mechanical vibration without resorting to light energy. Finally, this two-step synthesis technique combined with strain engineering allows us to create multifunctional soft micromotors, i.e., the ZnO-NWs/PDMS submillimeter 3D structures integrated with various nanomaterials (metal nanoparticle catalysts, magnetic nanoparticles, etc.). The micromotors possess multiple functionalities such as photocatalysis, piezoelectrocatalysis, locomotion/self-propulsion, and magnetic response. This level of multifunctionality integration on a single platform can be rarely found in the literature. In the end, an immobilized photocatalytic system with high surface areas, improved mass transfer, and easy recyclability has been developed, which can find its uses in biomedical and environmental applications. Apart from the photocatalytic applications, the research has also been oriented to address some technical challenges in deterministic assembly of the solution-processed 1D nanostructures for device integration."--Pages ii-iii.
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Title: Experimental and numerical investigation of confined premixed flame
Creator: Najim, Younis Mahal
Date: 2017
Collection: Electronic Theses & Dissertations
Description: Understanding the dynamics of premixed flames propagating during constant volume combustion is key to enhancing the performance of existing combustion devices, which provide 80% of the world’s energy supply, and reducing the impact of pollution on the environment. This work experimentally and numerically investigates confined premixed flame propagation in an initially quiescent mixture. Three combustion chambers are used; a curved wave disc engine channel and rectilinear channels of aspect...
Show moreUnderstanding the dynamics of premixed flames propagating during constant volume combustion is key to enhancing the performance of existing combustion devices, which provide 80% of the world’s energy supply, and reducing the impact of pollution on the environment. This work experimentally and numerically investigates confined premixed flame propagation in an initially quiescent mixture. Three combustion chambers are used; a curved wave disc engine channel and rectilinear channels of aspect ratio 7 and 10. The mixture is methane/air and syngas (H2/CO)/air initially at atmospheric pressure and room temperature. The channel walls are assumed to be isothermal to incorporate the effect of heat transfer. For two-dimensional analysis, the reaction rate is modeled using both detailed and reduced kinetic mechanisms. The mass diffusion is investigated using three different diffusion models with different levels of approximation; the multicomponent diffusion model of Chapman-Enskog including the Soret effect; the mixture-averaged model; and constant Lewis number. For three-dimensional analysis, a large eddy simulation coupled with the transport equation of the reaction progress variable is used. In this work, the reaction rate predicted using the Boger model of algebraic flame surface density is modified by incorporating a transient flame speed that accounts for the variation in the temperature and pressure of the unburned gases. The experimental measurements include schlieren photography to track the flame structure and propagation speed, and the pressure-time history during the combustion process is measured by a pressure sensor mounted in the channel wall. The experimental measurements validate the numerical simulation results and provide further understanding of the flame and pressure dynamics. Unlike behavior previously reported in straight or 90◦ bend channels, premixed flame propagation in the wave disc engine channel exhibits different features: the convex tulip flame converts back into a concave flame and thus reveals the influence of channel geometry on flame evolution. The experiments show that the rate of pressure change eventually becomes negative mainly due to heat losses that engender a correspondingly slower flame propagation during the final stage of burning. The analysis of the numerical results reveals the effect of the interaction between the flame front, pressure field, and flame-induced flow on flame evolution during all stages of flame structure development. The results also demonstrate that both multicomponent diffusion with the Soret effect and the mixture-averaged model produce slightly different results in flame speed, structure, peak temperature, and average pressure for the methane/air mixture, while the deviation is more pronounced for syngas flames. The methane/air flame produced by the unity Lewis number model, however, lags behind its counterparts during early stages and dramatically accelerates, at which time the values of peak temperature and average pressure show unrealistic behavior. Furthermore, unity Lewis number flames develop an artificial second tulip flame after the first tulip flame is annihilated. This second tulip flame is neither observed in the Chapman-Enskog and mixture-average simulations, nor in the experiments. This reveals the role of the Lewis number in the intrinsic thermodiffusive flame instabilities and tulip flame formation. The three-dimensional simulation uncovers an interesting behavior for the flame structure that is introduced here as a “transverse tulip” flame, which has not been previously reported. The “transverse tulip” flame evolves in the direction perpendicular to that of the initial tulip flame after the latter undergoes the transition from cusped convex back to the concave finger shape. The commonly used Zimont model produces an unrealistically diffused flame front. The large eddy simulation coupled with the here-modified algebraic flame surface density overcomes this issue and reproduces the experimental observations of the flame structure, pressure-time history, and burning time with good agreement.
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Title: Finger-powered thermoplastic microfluidic electrochemical assay for diagnostic testing using a mobile phone
Creator: Lin, Tung-Yi
Date: 2018
Collection: Electronic Theses & Dissertations
Description: "Point-of-care (POC) testing has gained considerable attention in recent years due to its ability to provide diagnostic information without the need for centralized laboratory facilities or bulky equipment. This has been achieved, in part, by advances in micro-electro-mechanical system (MEMS) and analytical chemistry, which has resulted in the miniaturization and integration of sensitive biosensors and fluidic components. Recently, researchers have demonstrated the use of mobile phones for...
Show more"Point-of-care (POC) testing has gained considerable attention in recent years due to its ability to provide diagnostic information without the need for centralized laboratory facilities or bulky equipment. This has been achieved, in part, by advances in micro-electro-mechanical system (MEMS) and analytical chemistry, which has resulted in the miniaturization and integration of sensitive biosensors and fluidic components. Recently, researchers have demonstrated the use of mobile phones for POC testing, which offers the advantages of portability and wireless data transmission. Many mobile phone-based POC tests are based on optical imaging or colorimetric assays, which are useful for some diagnostic applications, but lack the accuracy and sensitivity required for the diagnosis of many important diseases. Moreover, these devices employ microfluidic chips fabricated using glass, polydimethylsiloxane (PDMS) or paper, which require complex microfabrication or surface treatments, or offer limited fluidic control. In this dissertation, we explored the development of plastic-based microfluidic chips for rapid electrochemical measurements of protein biomarkers using a mobile phone biosensing platform. We first investigated UV/ozone (UVO) surface treatment on plastics to better understand its usefulness for microfluidic POC applications. We found that UVO-treated poly(methyl methacrylate) (PMMA), cyclic olefin copolymer (COC) and polycarbonate (PC) experience hydrophobic recovery within 4 weeks and the rate at which it occurs is dependent on the UVO treatment duration. Furthermore, we discovered that the hydrophobic recovery of UVO-treated COC and PC can be inhibited by storing them in dehumidified or vacuum conditions. UVO-treated plastics were also used for protein adsorption measurements, which showed that UVO treatment minimized protein adsorption and this effect is correlated with the treatment duration. Lastly, we demonstrated capillary-driven flows in UVO-treated PMMA microchannels, which revealed that the flow rate can be tuned by adjusting the treatment duration. We also explored the development of new fabrication methods for generating plastic microfluidic devices. In particular, we have demonstrated for the first time the use of 3D printed metal molds for fabricating plastic microchannels via hot embossing. Through the optimization of the powder composition and processing parameters, we generated stainless steel molds with superior material properties (density and surface finish) and replication accuracy compared with previously reported 3D printed metal parts. 3D printed molds were used to fabricate PMMA replicas, which exhibited good feature integrity and replication quality. Microchannels fabricated using these replicas exhibited leak-free operation and comparable flow performance as microchannels fabricated from CNC milled molds for both capillary and pressure-driven flows. Toward the realization of a shelf stable, electricity-free microfluidic assay for POC testing, we developed a finger-powered microfluidic chip for electrochemical measurements of protein biomarkers. This device employs a valveless, piston-based pumping mechanism which utilizes a human finger for the actuation force. Liquids are driven inside microchannels by pressing on a mechanical piston, which generates a pressure-driven flow. Dried reagents are preloaded in microwells allowing for the entire testing process to be completed on-chip. Additionally, a nonenzymatic detection scheme is employed which circumvents the need for refrigeration. For proof-of-concept, this microfluidic assay was coupled with a mobile phone biosensing platform for quantitative measurements of Plasmodium falciparum histidine-rich protein-2 (PfHRP2) in human blood samples. Using this platform, PfHRP2 was detected from 1 to 20 æg/mL with high specificity and each measurement could be completed in 2264 5 min. In addition, this assay can be stored at room temperature for up to one month with a negligible loss in performance. The results and knowledge presented in this dissertation will provide new insights into the development of plastic microfluidic devices for POC testing as well as other biomedical application."--Pages ii-iii.
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Title: A Stirling engine for use with lower quality fuels
Creator: Paul, Christopher J.
Date: 2014
Collection: Electronic Theses & Dissertations
Description: There is increasing interest in using renewable fuels from biomass or alternative fuels such as municipal waste to reduce the need for fossil based fuels. Due to the lower heating values and higher levels of impurities, small scale electricity generation is more problematic. Currently, there are not many technologically mature options for small scale electricity generation using lower quality fuels. Even though there are few manufacturers of Stirling engines, the history of their development...
Show moreThere is increasing interest in using renewable fuels from biomass or alternative fuels such as municipal waste to reduce the need for fossil based fuels. Due to the lower heating values and higher levels of impurities, small scale electricity generation is more problematic. Currently, there are not many technologically mature options for small scale electricity generation using lower quality fuels. Even though there are few manufacturers of Stirling engines, the history of their development for two centuries offers significant guidance in developing a viable small scale generator set using lower quality fuels. The history, development, and modeling of Stirling engines were reviewed to identify possible model and engine configurations. A Stirling engine model based on the finite volume, ideal adiabatic model was developed. Flow dissipation losses are shown to need correcting as they increase significantly at low mean engine pressure and high engine speed. The complete engine including external components was developed. A simple yet effective method of evaluating the external heat transfer to the Stirling engine was created that can be used with any second order Stirling engine model. A derivative of the General Motors Ground Power Unit 3 was designed. By significantly increasing heater, cooler and regenerator size at the expense of increased dead volume, and adding a combustion gas recirculation, a generator set with good efficiency was designed.
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Title: Textile-based electrochemical sensors and batteries for wearable biosensing
Creator: Liu, Xiyuan (College teacher)
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "In this work, we explored the development of robust, textile-based electrochemical sensors and batteries for wearable sensing applications." -- Abstract.

Title: Design and performance analysis of gas and liquid radial turbines
Creator: Tan, Xu
Date: 2016
Collection: Electronic Theses & Dissertations
Description: "In the first part of the research, pumps running in reverse as turbines are studied. This work uses experimental data of wide range of pumps representing the centrifugal pumps' configurations in terms of specific speed. Based on specific speed and specific diameter an accurate correlation is developed to predict the performances at best efficiency point of the centrifugal pump in its turbine mode operation. The proposed prediction method yields very good results to date compared to previous...
Show more"In the first part of the research, pumps running in reverse as turbines are studied. This work uses experimental data of wide range of pumps representing the centrifugal pumps' configurations in terms of specific speed. Based on specific speed and specific diameter an accurate correlation is developed to predict the performances at best efficiency point of the centrifugal pump in its turbine mode operation. The proposed prediction method yields very good results to date compared to previous such attempts. The present method is compared to nine previous methods found in the literature. The comparison results show that the method proposed in this paper is the most accurate. The proposed method can be further complemented and supplemented by more future tests to increase its accuracy. The proposed method is meaningful because it is based both specific speed and specific diameter. The second part of the research is focused on the design and analysis of the radial gas turbine. The specification of the turbine is obtained from the solar biogas hybrid system. The system is theoretically analyzed and constructed based on the purchased compressor. Theoretical analysis results in a specification of 100lb/min, 900ºC inlet total temperature and 1.575atm inlet total pressure. 1-D and 3-D geometry of the rotor is generated based on Aungier's method. 1-D loss model analysis and 3-D CFD simulations are performed to examine the performances of the rotor. The total-to-total efficiency of the rotor is more than 90%. With the help of CFD analysis, modifications on the preliminary design obtained optimized aerodynamic performances. At last, the theoretical performance analysis on the hybrid system is performed with the designed turbine."--Pages ii-iii.
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