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Title: DESIGN AND PERFORMANCE ASSESSMENT OF MULTI-MODAL MOBILE ROBOTS
Creator: Kalantari, Arash
Date: 2015, 2015-05
Description: This thesis is focused on developing multi-modal mobile robots, i.e. robots that can operate in more than one domain. For decades, researchers...
Show moreThis thesis is focused on developing multi-modal mobile robots, i.e. robots that can operate in more than one domain. For decades, researchers have been trying to improve locomotion capabilities of robots that operate in a single domain: on the ground, on inclined surfaces, in the air, or in water. A prevailing approach in design of hybrid robots is to simply attach systems designed for a single domain together. In order to reduce the complexity of the hybrid robot, a different design approach is taken in this thesis by attempting to keep the hardware resources on the system as low as possible. To this end, two hybrid aerial and terrestrial platforms have been developed: the walking quadrotor and the HyTAQ, the Hybrid Terrestrial and Aerial Quadrotor. In both platforms, ight is achieved through a quadrotor configuration; four actuators provide the required thrust. The walking quadrotor uses a single actuator set for both walking and ying by means of a unique compliant mechanism. This mechanism uses two separate linear movements to make walking possible. The horizontal movement of the leg is driven by running the propellers in reverse and the vertical movement is actuated by shape memory alloy (SMA) wires. An experimental prototype of this robot proves the functionality of the design. However, the experiments suggest that the application of the robot is efficient only where ground movement is a small portion of the whole mission. This is mainly due to the low efficiency of the propellers rotating in reverse and large time constant of the SMA wires, which makes walking slow. The terrestrial locomotion of HyTAQ has been made possible by adding a cylindrical cage, connected to the quadrotor through a revolute joint. This allows the cage to roll freely with respect to the body of the quadrotor, making the terrestrial locomotion possible. Moreover, the same ight actuators and control commands can be used to control terrestrial mode. An analysis of the system's energy consumption shows that the addition of the terrestrial locomotion improves the efficiency of the aerial-only quadrotor by increasing the overall operation range and time. This has been experimentally verified by showing that the HyTAQ's terrestrial range is 11 times greater compared to ight range of the quadrotor at the same speeds. Developing a hybrid aerial and scansorial robot is the next goal of this research. The first step toward this goal has been taken as part of this thesis by developing a method that enables a quadrotor to land and take-off from smooth vertical surfaces autonomously. A Microsoft Kinect sensor is used to localize the MAV and a PID controller is used to control the perching maneuver. A servo actuated gripper, mounted in front of the robot, makes attachment and detachment possible. The experimental results show that the robot can perch successfully in more than 90% of the experiments, which indicates the robustness of the proposed method.
Ph.D. in Mechanical and Aerospace Engineering, May 2015
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Title: ADVANCED MATERIALS ENABLED BY ATOMIC LAYER DEPOSITION FOR HIGH ENERGY DENSITY RECHARGEABLE BATTERIES
Creator: Chen, Lin
Date: 2017, 2017-05
Description: In order to meet the ever increasing energy needs of society and realize the US Department of Energy (DOE)’s target for energy storage,...
Show moreIn order to meet the ever increasing energy needs of society and realize the US Department of Energy (DOE)’s target for energy storage, acquiring a fundamental understanding of the chemical mechanisms in batteries for direct guidance and searching novel advanced materials with high energy density are critical. To realize rechargeable batteries with superior energy density, great cathodes and excellent anodes are required. LiMn2O4 (LMO) has been considered as a simpler surrogate for high energy cathode materials like NMC. Previous studies demonstrated that Al2O3 coatings prepared by atomic layer deposition (ALD) improved the capacity of LMO cathodes. This improvement was attributed to a reduction in surface area and diminished Mn dissolution. However, here we propose a different mechanism for ALD Al2O3 on LMO based on in-situ and ex-situ investigations coupled with density functional theory calculations. We discovered that Al2O3 not only coats the LMO, but also dopes the LMO surface with Al leading to changes in the Mn oxidation state. Different thicknesses of Al2O3 were deposited on nonstoichiometric LiMn2O4 for electrochemical measurements. The LMO treated with one cycle of ALD Al2O3 (1×Al2O3 LMO) to produce a sub-monolayer coating yielded a remarkable initial capacity, 16.4%higher than its uncoated LMO counterpart in full cells. The stability of 1×Al2O3 LMO is also much better as a result of stabilized defects with Al species. Furthermore, 4×Al2O3 LMO demonstrates remarkable capacity retention. Stoichiometric LiMn2O4 was also evaluated with similar improved performance achieved. All superior results, accomplished by great stability and reduced Mn dissolution, is thanks to the synergetic effects of Al-doping and ALD Al2O3 coating.Turning our attention to the anode, we again utilized aluminum oxide ALD to form conformal films on lithium. We elaborately designed and studied, for the first time, the growth mechanism during Al2O3 ALD on lithium metal in-situ quart crystal microbalance (QCM) measurements and found larger growth than expected during the initial cycles. Besides, we discovered that electrolytes show much enhanced wettability on Li with Al2O3 coating, leading to uniform and dense solid electrolyte interphase formation as well as less electrolyte required for battery operations. Also, we achieved more than 2 times longer cycling life with protected Li and obtained Coulombic efficiencies as high as ~98% at a practical current rate of 1 mA/cm2, compared to bare Li. More significantly, when the electrolyte volume is limited (10 μL and 5 μL), the cycling life is about 4 times longer. X-ray photoelectron spectroscopy (XPS) for electrodes after cycles and in-situ transmission electron microscopy (TEM) demonstrate that most of lithium is deposited beneath the film. The more uniform Al2O3 coated lithium after cycling observed by scanning electron microscopy (SEM) verifies that ALD Al2O3 isexceptionally effective to prevent lithium dendrite formation. These results demonstrate that ALD Al2O3 coatings offer a promising route towards energy storage devices that utilize lithium metal anodes, such as Li-S batteries.
Ph.D. in Materials Science and Engineering, May 2017
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Title: LEAKAGE DETECTION AND QUANTIFICATION TECHNIQUES USING VARIOUS METHODS OF NEARFIELD ACOUSTIC HOLOGRAPHY
Creator: Chelliah, Kanthasamy
Date: 2016, 2016-07
Description: This thesis proposes an acoustic technique to detect and relatively quantify leakages in buildings and enclosures using various methods of...
Show moreThis thesis proposes an acoustic technique to detect and relatively quantify leakages in buildings and enclosures using various methods of nearfield acoustic holography (NAH). This laboratory study was performed on a scaled, wooden building model. Known leakages can be created in the wooden model and the acoustic method was tested to localize and relatively quantify these known leakage areas. An acoustic source was placed inside the building model and a planar hologram measurement was performed near the surface of the building model. Various methods of NAH were applied on the hologram data to reconstruct the sound pressure field on the wall of the building model. The detection and quantification capabilities of four different NAH methods, namely, discrete Fourier transform (DFT) based NAH, equivalent source model (ESM) based NAH, boundary element method (BEM) based NAH and statistically optimized NAH (SONAH), were compared in this study. It was shown that the NAH methods were able to successfully locate and relatively quantify the area of the leakages using the reconstructions. Although all the four algorithms produced comparable results in the very nearfield, at larger hologram distances, ESM and SONAH reconstructions were more accurate than the reconstructions using the other methods. Although, ESM and SONAH produced similar results for most of the cases, ESM is more preferable due to its simplicity in implementation and less computational time requirements. Lower frequency reconstructions were found to be more accurate and advantageous in the context of leakage detection and quantification. When the hologram distance was increased more than a particular limit, all the four algorithms arrive at inaccurate reconstructions due to the very ill-conditioned propagation matrices. New filtering methods to alleviate these larger reconstruction errors were introduced and the results were demonstrated. Effects of large sensor phase mismatch were also studied. It was demonstrated that larger phase error in the measurements could result in less accurate reconstructions. Performances of various regularization parameter choice methods applied to different approaches of nearfield acoustic holography were compared at various distances of reconstructions. Generalized cross validation and Morozov methods were implemented to arrive at filtering parameters to regularize the NAH reconstructions. Morozov method did not provide any significant filtering for the geometries considered in this study. GCV method produced very accurate reconstructions when a very nearfield measurement was supplied. Four new parameter choice methods were introduced to obtain the appropriate regularization parameters for very ill-conditioned inverse problems such as NAH. These methods work very well even at larger hologram distances and when the matrix dimension is very large where other available methods fail. These new parameter choice methods are not specific for the NAH problem. They can be applied to any ill-conditioned inverse problem. The advantages of each parameter choice method were explored and discussed in detail. Effects of signal quality on the NAH reconstructions were also studied. Patch NAH was implemented successfully to extend the aperture of computational domain more than that of the measurement. Also, the challenges in obtaining a smooth solution through patch NAH were discussed. A unique, MEMS based microphone array was designed, fabricated and tested keeping the future field tests in mind. The tests show that this array produces reasonably accurate measurements that can be used for the NAH methods. GCV method was found to work well for the reconstructions from the array even at larger distances because of the smaller propagation matrix due to the less number of microphones. This portable array can be used for field tests due to its portable form factor and reasonably accurate reconstructions.
Ph.D. in Mechanical and Aerospace Engineering, July 2016
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Title: EFFECTS OF ARRAY SCALING ON THE ANGULAR RESOLUTION OF MICROPHONE ARRAY SYSTEMS
Creator: Aldeman, Matt
Date: 2016, 2016-12
Description: Array detection systems have been in use for nearly a century and have proven useful in a variety of applications. The most ubiquitous form of...
Show moreArray detection systems have been in use for nearly a century and have proven useful in a variety of applications. The most ubiquitous form of array is the active radar array, but in the past four decades microphone arrays have become increasingly common. Microphone arrays have traditionally been very large devices. This is because of the limited angular resolution of the traditional Delay-and-Sum (DAS) beamforming algorithm. Improved frequency-domain beamforming (FDBF) methods were developed in the 1980’s using the Fast Fourier Transform. More advanced methods have been developed in the past decade, including deconvolution methods (DAMAS, DAMAS2), methods based on the spatial coherence of point sources and sidelobes in the frequency domain (CLEAN-SC), and spatial coherence methods in the time domain (TIDY). In this investigation two sets of experiments were carried out to better understand the angular resolution characteristics of scaled microphone arrays and associated beamforming algorithms. In the first experiment five scaled microphone arrays with diameters from 0.73m to 10.98m were constructed and tested, and the data was analyzed with a variety of beamforming algorithms. In the second experiment three scaled microphone arrays and one alternative array geometry were tested with both free-field and reflective boundary conditions. The results show that the Rayleigh criterion can be exceeded under certain conditions. However, several other parameters are also important. For example, Signal-to-Noise Ratio (SNR), z-axis correction, and reflective boundaries all impact aspects of the array’s performance. In addition to increasing the array diameter and the signal frequency, results show that effective strategies to improve the angular resolution performance of an array include careful selection of beamforming algorithm, the use of appropriate beamforming integration times, and minimizing boundary reflections. The DAS algorithm is shown to offer the lowest angular resolution performance because it does not separate the acoustic source map from the point spread function of the array. The DAMAS algorithm offers the greatest angular resolution because it numerically deconvolutes the acoustic source map from the point spread function. However, deconvolution-based algorithms are the most negatively affected by the boundary reflection effects commonly seen with larger arrays. This is because the pressure field becomes contaminated with reflections and image sources, and the deconvolution approach does not make use of significant simplifying assumptions as several of the other algorithms do. The logarithmic spiral array is shown to offer versatile performance across a wide range of frequencies, while an alternative quasiperiodic array yields results that are highly frequency-dependent. It is demonstrated that this is because of gaps in the source-to-element differences coverage, and the gaps in coverage correspond to half-wavelengths of frequency bands with significantly lower angular resolution performance.
Ph.D. in Mechanical and Aerospace Engineering, December 2016
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Title: MECHANICAL PROPERTIES AND DEFORMATION MECHANISMS OF TERNARY γ-γ’-δ NICKEL-BASED SUPERALLOYS
Creator: Di Sciullo Jones, Alexander
Date: 2012-12-03, 2012-12
Description: The primary drive towards the continued development of nickel-based superalloys lies in the turbine industry, both for propulsion and power...
Show moreThe primary drive towards the continued development of nickel-based superalloys lies in the turbine industry, both for propulsion and power generative uses, where approximately 90% of such materials are used. The ongoing trend is to increase the temperature, increase the rotational speed, and decrease the weight of turbines to increase their efficiency. Thus, much of the improvement of the efficiency of these machines rests on what materials are available to the industry. This has led to the design of superalloys specifically tailored to withstand the varied and increasingly demanding properties of turbine parts. Turbine discs, as one such part, experience substantially lower temperatures than the turbine blades, thus the creep properties of materials to be used in such an application are not quite as important. However, in the drive to increase turbine rotation speed and reduce weight, the industry is looking for materials which can withstand higher stresses. It is with this goal in mind that the material focused on in this work, V204H, was designed. The material utilizes a novel, three-phase microstructure consisting of γ-γ’-δ rather than a conventional two-phase γ-γ’ microstructure. It has been theorized that the addition of δ precipitates, formed through the addition of niobium, will behave as a reinforcement phase as in a particulate composite. The material was also heavily alloyed to increase strengthening and improve creep behavior via the addition of elements which decrease diffusion rate and deter grain boundary damage. It was discovered that this material has a fourth phase between the γ’ precipitates, and this was identified using SAD to be γ”. Flow stress tests over a range of temperatures and creep tests, both performed in compression, were conducted. These properties were seen to be exemplary for use in a turbine disc. It was, however, found that such properties deteriorated when the testing was conducted in tension. This xv
M.S. in in Materials Science and Engineering, December 2012
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Title: GRAIN BOUNDARY ENGINEERING IN INCONEL 600
Creator: Li, Baishun
Date: 2013, 2013-12
Description: Grain Boundary Engineering (GBE) is a process consisting of deformation-anneal iterations that increase special boundaries, especially the...
Show moreGrain Boundary Engineering (GBE) is a process consisting of deformation-anneal iterations that increase special boundaries, especially the fraction of Σ3 boundaries, to improve material properties such as corrosion resistance, intergranular fracture resistance or ductility. In this work, Inconel 600 super alloy was chosen as the research material. Different levels of compression at various temperatures followed by a subsequent anneal were used on the Inconel 600 to investigate the respective Σ3 boundary fractions as a function of processing. Orientation Image Microscopy (OIM) was applied to scan, observe and analyze the microstructures of the samples before and after deformation. The work was aimed at investigating the effect of hot deformation on the Σ3 boundary fraction in Inconel 600 and understanding the mechanisms of Grain Boundary Engineering. The formation of twins was studied with emphasis on their formation following elevated temperature deformation.
M.S. in Material Science and Engineering, December 2013
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Title: ELECTROSTATIC SPRAY DEPOSITION OF SOLID OXIDE FUEL CELL ELECTROLYTE
Creator: He, Quanzhi
Date: 2013-04-30, 2013-05
Description: 8mol% yttria-stabilized zirconia (YSZ) is the most currently used electrolyte material for solid oxide fuel cell (SOFC) due to is chemical and...
Show more8mol% yttria-stabilized zirconia (YSZ) is the most currently used electrolyte material for solid oxide fuel cell (SOFC) due to is chemical and thermal stability and its high oxygen ion conductivity at high temperature. However, SOFC based on YSZ electrolyte operate generally at very high temperatures (900-1000℃) for adequate oxygen conductivity, therefore the selection of materials for other cell components has a lot of problems, such as high materials costs and degradation of performance. To avoid the problem associated with high temperatures, it would be desirable to reduce the operating temperature from 900℃ to intermediate temperatures, typically 600-800℃. But, at these temperature, the ohmic losses due to the low ionic conductivity of the electrolyte become too high for thick (100μm) YSZ electrolyte. Therefore, a thin (less than 10μm) but dense and tight electrolyte is needed. Because the thin film YSZ electrolyte makes the oxygen ions have a shorter conducting path, unit cells have less ohmic resistance at a reduced temperature. To make SOFC working at intermediate temperature, a thin (less than 10μm) but dense and tight electrolyte is needed. This work takes a closer look at electrostatic spraying of ceramic suspensions and the ability of sprayed layer to sinter into dense layer under the 10μm thickness range. In this study, a new ESD deposition system was designed and produced, the relationship between ESD parameters and the deposition results was established, most of all, pore free and complete dense ultra-thin YSZ electrolyte thin film (less than 1μm) was successfully made with ESD technique.
M.S. in MaterialsS ciencea ndE ngineering, May 2013
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Title: COMPUTATION OF THIN AIRFOIL AERODYNAMICS FOR MICRO AIR VEHICLE APPLICATIONS
Creator: Baez Guada, Alejandro
Date: 2013-04-29, 2013-05
Description: With the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main...
Show moreWith the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main challenge in enhancing flight conditions. The current flow control techniques are limited at suppressing fluctuations in the lift induced by unsteady freestreams and while undergoing fast maneuvers. As a result of the time delay associated with the actuation input and formation of the leading edge vortex, closed-loop controllers are limited by the bandwidth to suppress fluctuation in the lift under unsteady freestreams. Therefore, the recognition of the direct interaction of the controller with the formation of vortex shedding suggests the development of new techniques for flow control. For the sinusoidal oscillating freestream, the knowledge of the time scales in response to actuation and the phase between the unsteady freestream and lift time series are useful in the implementation of the feed forward controllers suppressing lift fluctuations. Moreover, prospective solutions have been conceptualized in the implementation of the leading edge separation sensor and the gust load alleviation controller that would allow the instantaneous response to enhance lift under unsteady freestreams conditions. With the increasing computational power and reliance on turbulence models, the numerical simulations facilitate the investigation of thin airfoil aerodynamics at post-stall angles of attack under steady and unsteady freestreams. The computations of turbulent flows for external flow aerodynamics are challenging as a result of the presence of separated flow. The detachment of boundary layers is by nature three-dimensional and time dependent. Therefore, simulating these flows is problematic and requires high computational cost. Thin shear layers are common in external aerodynamic flows demanding very fine near-wall discretization to solve for separation points. The growth of the boundary layer, separation, and mixing length scales require complex approaches for accurate results. xviii In the present study, the performance of the turbulence models is investigated in numerical predictions of thin airfoil aerodynamics at post-stall angles of attack. The results suggest that low computational cost turbulence models fail at treating separated flows. Moreover, the instantaneous locations of separation and stagnation points in response to the changes in the lift for steady and unsteady flows were investigated. The amplitude and frequency of the time series of the separation and stagnation point location are highly correlated with the characteristics of the lift oscillations. Therefore, the recognition of separation or stagnation point locations at the leading edge of the wing could provide the direct information of the gains and drops in the lift for active flow control applications.
M.S. in Aerospace and Mechanical Engineering, May 2013
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Title: DOUBLE AGING AND THERMOMECHANICAL HEAT TREATMENT OF ALUMINUM EXTRUSIONS
Creator: Emani, Satyanarayana
Date: 2012-08-27, 2012-12
Description: Double aging and thermo mechanical treatment of AA7075 and AA6061 aluminum alloys was studied and optimized to accelerate the kinetics of...
Show moreDouble aging and thermo mechanical treatment of AA7075 and AA6061 aluminum alloys was studied and optimized to accelerate the kinetics of aging process. This novel process is highly energy efficient and reduces the time of heat treatment of AA7075 alloys by 96%. It also achieves excellent mechanical properties compared to the conventional T6 heat treatment while improving ductility and energy efficiency. Hardness curves for different aging times and temperatures and TEM analysis was used to develop an empirical model was which explains the precipitation mechanism of η’ precipitates on GP zones and the effect of time and temperature on the double aging process.
PH.D in Materials Science, December 2012
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Title: RECRYSTALLIZATION MECHANISM FOR TWO NICKEL BASED SUPERALLOYS
Creator: Balandra, Ombeline
Date: 2016, 2016-05
Description: The demand for enhanced structural performances materials is growing every year. A lot of technological advancements in the sector of...
Show moreThe demand for enhanced structural performances materials is growing every year. A lot of technological advancements in the sector of aerospace or nuclear are in constant need for materials with good mechanical properties and high temperature resistance. The alloys commonly used for these features are Nickel-based superalloys as they exhibit high strength and good resistance to corrosion and oxidation. To improve their mechanical behavior, recent studies have focused on grain refinement methods. Among these methods to obtain the finest grain size distribution, one is particularly advantageous for it low cost and feasibility: severe plastic deformation.In this study, the deformation mechanism of two high performance, low stacking fault energy nickel-based alloys are investigated. The first alloy, Monel 400, it is a single FCC phase material. The second one is Inconel 625 wich has a two-phase (γ and γ’) microstructure. During hot deformation, the γ’ precipitate may be present in the γ phase and above a certain solvus temperature, the γ phase exists in the material. The restoration mechanism for FCC crystals is well known, and particular attention was given in this report to the recrystallization response and flow behavior of Inconel 625 for sub-solvus temperatures. In the introduction a brief review of the current state of literature on the deformation response of Nickel-based superalloys is provided. Samples were compressed under various temperatures and strain rate conditions using a Gleeble-3500 thermo-mechanical simulator and flow stress curves were extracted. To characterize both qualitatively and quantitatively the deformation, samples were then analyzed using standard microscopy, scanning electron microscopy and electron backscatter diffraction analysis. The resulting images and maps combined with flow stress curves have lead to the formulation of constitutive models of the recrystallization process using three parameters, the stress, grain size and recrystallized volume fraction.The data shows that deformation is first accommodated through dynamic recovery with the formation of sub-grains structures. Then, after the experimental strain reaches a critical value, recrystallized grains form within the microstructure. EBSD analysis show a trend for new recrystallized grain to grow under certain conditions. Results show a trend of increasing the grain size with increasing the strain and decreasing the Zener-Hollomon parameter and an increasing recrystallized volume fraction with increasing the strain and Zener-Hollomon parameter.
M.S. in Material, Mechanical and Aerospace Engineering, May 2016
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Title: VALIDATION AND CHARACTERIZATION OF TURBULENCE IN AN AORTIC COARCTATION
Creator: Arzani, Amirhossein
Date: 2012-04-25, 2012-05
Description: Image based, patient speci c computational uid dynamics (CFD) modeling has gained dramatic attention in evaluation of health and disease...
Show moreImage based, patient speci c computational uid dynamics (CFD) modeling has gained dramatic attention in evaluation of health and disease progression. With the popularity of these techniques in clinical settings the need to address how these numerical predictions validate against the empirical data becomes more imperative. Validation studies have primarily been used in vitro models, since experiments are dif- cult to control in vivo, and in vivo conditions are challenging to replicate numerically. However, in vivo validations are essential for a more reliable assessment. Moreover, direct quanti cation of turbulence, necessary for diagnostic purposes, makes the validation process more challenging in turbulent ows. A phase-contrast magnetic resonance imaging (PCMRI) method was used to obtain turbulent kinetic energy (TKE) in an aortic coarctation, a congenital disease, where the aorta narrows blocking the passage of blood to a great portion of the body. A 3D patient-speci c computer model of the aortic coarctation was constructed from the MRI data. Direct numerical simulation was performed to solve the Navier-Stokes equations using a stabilized nite element method. Based on the PCMRI procedures, di erent methods were used to compute TKE from the CFD velocity data, and were compared to the PCMRI data. The velocity data obtained from CFD was also used to study the ow topology by computing the Finite-Time Lyapunov Exponent (FTLE) eld, and the Lagrangian coherent structures (LCS). The TKE results showed relative good agreement between the in vivo measurements and the CFD predictions of TKE. Observed di erences were within expectations due to modeling, measurement and numerical errors.
M.S. in Mechanical, Materials, and Aerospace Engineering, May 2012
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Title: THE DEVELOPMENT OF A CRYOGENIC OVER-PRESSURE PUMP
Creator: Alvarez, Matthew L.
Date: 2001-07-17, 2012-07
Description: The Dark Energy Survey (DES) project will study the accelerated expansion of the universe. In order to further study this phenomenon,...
Show moreThe Dark Energy Survey (DES) project will study the accelerated expansion of the universe. In order to further study this phenomenon, scientists have devised a method of creating an array of charged couple devices (CCD) to capture images that will be studied. These CCDs must be cooled and remain at 173K to eliminate thermal gradients and dark current. Therefore, a two-phase CCD liquid nitrogen (LN2) cooling system was designed to maintain the array of CCDs at a constant temperature. However, the centrifugal pump used to supply LN2 has a mean time between failure (MTBF) of approximately two thousand-eight hundred hours (116 days). Because of the low MTBF of the centrifugal pump, a new pump is being considered to replace the existing one. This positive displacement pump is a simpler design that is expected to have a MTBF that will exceed 116 days (2800hrs). This positive displacement reciprocating pump, also known as, the cryogenic over-pressure pump (OPP), was tested in February 2012 and successfully cooled the CCD array to 173K. Though un t for service for DES CCD cooling system, the overall concept of this pump has been proven. Typical ow rates, pressures, and temperatures trends have been captured via instrumentation and are speci c to the operation of future over-pressure pumps.
M.S. in Mechanical and Aerospace Engineering, July 2012
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Title: AN ELECTRICITY-ASSISTED FRICTION STIR WELDING PROCESS WITH CURRENT APPLIED FROM THE WORKPIECE SIDE SURFACES
Creator: Eamkulworapong, Sakda
Date: 2011-11-09, 2011-12
Description: Friction stir welding (FSW) has many promising industrial applications due to its solid-state nature and the associated benefits. However,...
Show moreFriction stir welding (FSW) has many promising industrial applications due to its solid-state nature and the associated benefits. However, some challenges still exist, such as: (i) a high tool loading force is required to generate the friction heat needed to soften the material, which often limits tool life, and (ii) FSW often desires a narrow temperature range near but below the melting point, which makes it challenging to get a deep welding depth without melting the top surface. Electricity-assisted FSW (EAFSW) has been previously studied in literature, where the current is applied from the tool. The electricity generates additional resistance heat, which may increase the welding efficiency and decrease the required tool loading force. However, this approach yields a relatively high temperature gradient in the depth direction, and is difficult to effectively enhance the welding depth without melting the top surface. In this thesis, a new EAFSW process is proposed and studied, where the current is applied from the workpiece side surfaces. The study is based on an experimentally tested physics-based model, and it shows that the new EAFSW process has a great potential to enhance the welding efficiency, decrease the required tool loading force, and increase the welding depth without melting the top surface.
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Title: DESIGN OF MODERN HIGH NB-CONTENT ,-,' NI-BASE SUPERALLOYS
Creator: Antonov, Stoichko
Date: 2017, 2017-07
Description: Superalloy design can prove to be a very complex and challenging task, as certain elemental additions can significantly improve properties...
Show moreSuperalloy design can prove to be a very complex and challenging task, as certain elemental additions can significantly improve properties when added in high contents, however, exceeding their solubility limits can promote the formation of undesired phases at grain boundaries as well as grain interiors, and can quickly deteriorate the high temperature structural integrity and stability of the alloy, resulting in a catastrophic failure. Precipitate phases, such as " and ⌘, appear similar and are often mistaken for one another, leading to the need for a better fundamental understanding of their formation, required for developing innovative new classes of Ni-base superalloys. The morphology, formation, and composition of precipitate phases in a number of experimental alloys spanning a broad range of compositions were explored and compositional relationships were developed to facilitate the design of !-!0-("/⌘) Ni-base superalloys. The e↵ect of increasing Nb alloying additions on the formation and long term phase stability of topologically close packed (TCP) phases was studied. Elevated levels of Nb can result in increased matrix supersaturation and promote the precipitation of ⌘-Ni6AlNb along the grain boundaries in powder processed, polycrystalline Ni-base superalloys, while reduced Nb levels favored the precipitation of blocky Cr and Mo rich $ phase precipitates along the grain boundary. Evaluation of the thermodynamic stability of these two phases using Thermo-Calc showed that while $ phase predictions are fairly accurate, predictions of the ⌘ phase are limited. In addition, atom probe tomography (APT) was used to quantitatively assess grain boundary phase compositions and local segregation along the grain boundary before and after a 1000 hour thermal exposure at 800 "C. The complex network of $ phase precipitates that formed upon the thermal exposure and the characteristic interfacial segregation profiles were studied. In addition, elemental boron was observed to segregate to the grain boundary and phase interfaces, but did not form borides, due to the relatively low concentration of B atoms, resulting from a higher B concentration in the matrix. APT studies were also performed on MC carbides of the alloys and the formation kinetics and morphological differences between NbC and Hf doped NbC were explained using density functional theory (DFT) calculations of the formation energies of different facets of the MC carbide. Detailed electron microscopy and APT techniques were then used to systematically quantify the chemical and morphological instabilities that occur during aging of polycrystalline !-!0 Ni-base superalloys containing elevated levels of refractory alloying additions. The morphological changes and splitting phenomenon associated with the secondary !0 precipitates were related to the discrete chemical compositions of the secondary and tertiary !0 along with the phase compositions of the ! matrix and the ! precipitates that form within the secondary !0 particles. Compositional phase inhomogeneities led to the precipitation of finely dispersed tertiary !0 particles within the ! matrix and secondary ! particles within the secondary !0 precipitates, which, along with surface grooving of the secondary !0 particles, contributed to the inverse coarsening or splitting of the precipitates during aging. As recent studies have shown that polycrystalline Ni-base superalloys containing elevated levels of Nb additions exhibit superior properties at elevated temperatures when compared to existing commercial Ni-base superalloys, understanding of elemental partitioning to each phase is essential and was studied via APT. Compositions of the constituent phases were measured in four high Nb-content !-!0 Ni-base superalloys and the results were compared to thermodynamic database models from Thermo-Calc. Results were also used to predict the solid solution strength behavior of the four alloys. The di↵erences in phase composition predictions from thermodynamic models resulted in dissimilarities between the generated strength behavior curves and those from the experimental work. Finally, creep behavior of high Nb-content !-!0 Ni-Based superalloys was related to the formation of secondary phases mainly at grain boundaries. As secondary phases form, their brittle nature leads to crack formation, which can propagate under the tensile load and lead to premature failure of the alloy.
Ph.D. in Materials Science and Engineering, July 2017
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Title: SHIP STATE AND COVARIANCE PROPAGATION USING TIME SERIES ANALYSIS AND FORECASTING
Creator: Katre, Aniruddha
Date: 2014, 2014-05
Description: The Navy's Unmanned Combat Aerial System (N-UCAS) program is currently developing technology for autonomous shipboard landing of unmanned...
Show moreThe Navy's Unmanned Combat Aerial System (N-UCAS) program is currently developing technology for autonomous shipboard landing of unmanned aerial vehicles (UAVs). A high accuracy and high integrity relative navigation algorithm using carrier phase di erential GPS measurements and high rate inertial sensor data has been implemented to land the UAV. Such an algorithm requires ship state information to be broadcast to the aircraft via a VHF data link. The data link is susceptible to failure for reasons such as interference from jamming. This thesis considers the problem of precise ship state propagation on board an aircraft during a data link outage occuring when it is too late for the aircraft to abort its landing approach. Accurately quantifying the estimate error covariance is important for a high integrity and accuracy navigation algorithm. Therefore this thesis focuses on algorithms that can propagate the ship state as well as determine the propagation error covariance. Initially, a simple state propagation using kinematic equations for linear motion is tested. Seakeeping and Maneuvering theories used to model the dynamics of a sea vessel are also considered. However, analysis shows that due to constraints imposed by a data link outage and complexity in accurately modeling some parameters in the ship dynamic model, these two approaches are infeasible. As an alternative to kinematic and dynamic modeling, Time Series Analysis and Forecasting methods for ship state propagation are investigated. This work introduces parametric modeling and forecasting of a time series using linear stochastic models. Maximum likelihood estimate (MLE) and outer product of gradients (OPG) algorithms are implemented for faithful parameterization of time series using ARIMA models. Expressions for forecasting and forecast error variance quanti cation are also developed. These algorithms are then tested using ship data provided by the N-UCAS program.
M.S. in Mechanical and Aerospace Engineering, May 2014
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Title: A COUPLED LAGRANGIAN-EULERIAN MULTIPHASE MODEL FOR SIMULATION OF WIND TURBINES PERFORMANCE UNDER RAINY CONDITIONS
Creator: Cohan, Aiden C.
Date: 2016, 2016-05
Description: Wind Turbines power output is constantly influenced by their environmental conditions, including raining and icing. Therefore, understanding...
Show moreWind Turbines power output is constantly influenced by their environmental conditions, including raining and icing. Therefore, understanding the effect of rain is necessary to enhance the efficiency of the wind turbines used in regions with considerable number of rainy days and below freezing temperatures. We developed a multiphase computational fluid dynamics (CFD) model to estimate the effect of rain by simulating the actual physical process of rain droplets forming a water layer over the blades by coupling the conventional Lagrangian Discrete Phase Model (DPM) and the Eulerian Volume of Fluid (VOF) models. We first applied our model to the National Renewable Energy Laboratories (NREL) S809 airfoil used in the blade profile of horizontal-axis wind turbines (HAWT) and studied the effect of rain at different rainfall rates in addition to the effect of surface tension and surface property of the airfoil. Our simulations showed that surface tension has a dominant effect on the performance of the airfoil and should not be neglected under simulated rainy conditions. It also was observed that, under rainy conditions, an airfoil with non-wetting surface has an inferior performance (lower lift and higher drag coefficient) compared to an airfoil with wetting surface due to the added roughness caused by water on the non-wetting surface, which is in line with experimental observations. We also observed that, at low rainfall rates, the performance of the airfoil is highly sensitive to the rainfall rate. However, if the rainfall rate is high enough to immerse most of the airfoil surface under water, a further increase in the rainfall rate does not have a substantial effect on the performance of the airfoil. We also investigated the effect of rain at different angles of attack for two rainfall rates. We started by running single phase cases and observed that our results agreed well with experimental data. We then ran multiphase cases and observed that, lift coefficient increases with angle of attack even past the stall angle compared to the single phase case. However, this favorable increase in lift is accompanied by an increase in the drag coefficient which is greater at larger angles of attack. Finally, we simulated the performance of an actual 3D wind turbine (NREL phase VI horizontal axis wind turbine) for single phase cases at various wind speeds, in addition to, a multiphase case (under rainy conditions) using our multiphase model. Our single phase results compared well with experimental data. We had to use a simplified version of our multiphase model for the multiphase 3D simulation in order to make it computationally affordable. We observed that rain can reduced the performance of the NREL phase VI wind turbine by about 5% at a wind speed of 7.02 m/s and a rainfall rate of 40 mm/hr. Even though we used our multiphase model to simulate water layer formation from rain droplets, the physical concepts used in developing the model are very general and are not limited to this specific problem. Our model can be used to simulate any problem that involves particles hitting a surface and forming a liquid phase. For example, it can be used to model spray painting of a surface as the spray droplets form a paint layer on the surface.
Ph.D. in Mechanical, Materials and Aerospace Engineering, May 2016
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Title: Closed nozzle tests of a forty gallon chemical extinguisher
Creator: Corman, A., Cowles, R. D., Owen, W. R., Tronvig, W. P.
Date: 2009, 1917
Publisher: Armour Institute of Technology
Description: http://www.archive.org/details/closednozzletest00corm
Thesis (B.S.)--Armour Institute of Technology

Title: The Engineering Significance of Limit Analysis
Creator: Hodge, Philip G. Jr.
Date: 2011-05-12, 1958-04
Publisher: Department of Mechanics, Illinois Institute of Technology
Description: By definition, the limit load on a structure is the unique magnitude of the given loads under which a structure can first deform if it is made...
Show moreBy definition, the limit load on a structure is the unique magnitude of the given loads under which a structure can first deform if it is made of a rigid-perfectly plastic material. The significance of the limit load for a structure made of a real material is discussed in relation to a simple truss.
Sponsorship: Contract No. Nonr 140604
This research was sponsored by the federal government. The appropriate Department of Defense database, DTIC Online Access Controlled, was consulted prior to submission to confirm that the report has no distribution limitations and may therefore be made available to the public online.
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