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Articles 1 - 30 of 58
Full-Text Articles in Engineering
Carbon Nanotube Fibers: Mechanical Behavior And The Effects Of The Space Environment, Ryan A. Kemnitz
Carbon Nanotube Fibers: Mechanical Behavior And The Effects Of The Space Environment, Ryan A. Kemnitz
Theses and Dissertations
Carbon nanotube materials are promising multifunctional materials for incorporation into aerospace structures because of their high tensile strength, high electrical conductivity, and low density. This research aimed to characterize the mechanical failure mechanisms of carbon nanotube fibers and examine the effects of the space environment on their material properties. Tensile tests were conducted at varying strain rates and on fibers of varying gage lengths to examine the underlying molecular failure mechanisms and impact of defects on fiber strength. Tensile strength and elastic modulus were observed to increase with increasing strain rate and decrease with increasing gage lengths. The observed effects …
Thermal Management Of Satellite Electronics Via Gallium Phase Change Heat Sink Devices, Brian O. Palmer
Thermal Management Of Satellite Electronics Via Gallium Phase Change Heat Sink Devices, Brian O. Palmer
Theses and Dissertations
The purpose of this research was to determine the effectiveness and feasibility of additively manufactured heat sinks using gallium as a phase change material in the thermal management of satellite electronics. A design was created based on the footprint of an Astronautical Development, LLC Lithium 1 UHF radio and six heat sinks were additively manufactured; two each of stainless steel 316, Inconel 718, and ULTEM 9085. Each heat sink was filled with gallium for testing purposes. Models were created to simulate the behavior of the heat transfer and phase change processes occurring within the heat sink. Additionally, laboratory data was …
Experimental And Computational Analysis Of The Interaction Of Carbon And Silicon Ablation Products In Expanding Hypersonic Flows, Brian E. Donegan
Experimental And Computational Analysis Of The Interaction Of Carbon And Silicon Ablation Products In Expanding Hypersonic Flows, Brian E. Donegan
Theses and Dissertations
Thermal protection is required for vehicles entering planetary atmospheres to protect against the severe heating loads experienced. Characterization of candidate materials is often done utilizing plasma or arc-jet facilities, which provide steady-state testing of the thermal environments experienced during hypersonic flight, but do not correctly simulate hypersonic flowfields. Conversely, impulse facilities can reproduce flight velocities and enthalpies but have extremely short test times, prohibiting testing of thermal response. Modeling ablation and heating rates, particularly in the wake region, remains a significant challenge due to the complexity of the flowfield. To better understand this complex phenomenon and provide data to validate …
Reconstruction Of The 3d Temperature And Species Concentration Spatial Distribution Of A Jet Engine Exhaust Plume Using An Infrared Fourier Transform Spectrometer Hyperspectral Imager, Mason D. Paulec
Theses and Dissertations
The measurement of combustion byproducts is useful for determining pollution of any fuel burning application, efficiency of combustion, and determining detectability of aircraft exhausts. Both intrusive and non-intrusive techniques have been utilized to measure these quantities. For the majority of the non-intrusive techniques, the absorption and emission spectra of the gases are utilized for measurements. For this research, the use of the Telops Infrared Fourier Transform Spectrometer (IFTS) Hyperspectral Imager (HSI) was explored within the scope of combustion diagnostic methods, as an option for remote measurements of a jet turbine to determine concentration of species and temperature of the combustion …
A Heuristic Method For Task Selection In Persistent Isr Missions Using Autonomous Unmanned Aerial Vehicles, Christopher C. Olsen
A Heuristic Method For Task Selection In Persistent Isr Missions Using Autonomous Unmanned Aerial Vehicles, Christopher C. Olsen
Theses and Dissertations
The Persistent Intelligence, Surveillance, and Reconnaissance (PISR) problem seeks to provide timely collection and delivery of data from prioritized ISR tasks using an autonomous Unmanned Aerial Vehicle (UAV). In the literature, PISR is classified as a type of Vehicle Routing Problem (VRP), often called by other names such as persistent monitoring, persistent surveillance, and patrolling. The objective of PISR is to minimize the weighted revisit time to each task (called weighted latency) using an optimal task selection algorithm. In this research, we utilize the average weighted latency as our performance metric and investigate a method for task selection called the …
Application Of Spectral Solution And Neural Network Techniques In Plasma Modeling For Electric Propulsion, Joseph R. Whitman
Application Of Spectral Solution And Neural Network Techniques In Plasma Modeling For Electric Propulsion, Joseph R. Whitman
Theses and Dissertations
A solver for Poisson's equation was developed using the Radix-2 FFT method first invented by Carl Friedrich Gauss. Its performance was characterized using simulated data and identical boundary conditions to those found in a Hall Effect Thruster. The characterization showed errors below machine-zero with noise-free data, and above 20% noise-to-signal strength, the error increased linearly with the noise. This solver can be implemented into AFRL's plasma simulator, the Thermophysics Universal Research Framework (TURF) and used to quickly and accurately compute the electric field based on charge distributions. The validity of a machine learning approach and data-based complex system modeling approach …
Navigation With Artificial Neural Networks, Joseph A. Curro Ii
Navigation With Artificial Neural Networks, Joseph A. Curro Ii
Theses and Dissertations
The objective of this dissertation is to explore the applications for Artificial Neural Networks (ANNs) in the field of Navigation. The state of the art for ANNs has improved significantly so now they can rival and even surpass humans in problems once thought impossible. We present different methods to augment, combine, or replace existing Navigation filters with ANN. The main focus of these methods is to use as much existing knowledge as possible then use ANNs to extend the current knowledge base. Next, improvements are made for a class of Artificial Neural Network (ANN)s which provide covariance called Mixture Density …
Satellite Articulation Sensing Using Computer Vision, David H. Curtis
Satellite Articulation Sensing Using Computer Vision, David H. Curtis
Theses and Dissertations
Autonomous on-orbit satellite servicing benefits from an inspector satellite that can gain as much information as possible about the primary satellite. This includes performance of articulated objects such as solar arrays, antennas, and sensors. A method for building an articulated model from monocular imagery using tracked feature points and the known relative inspection route is developed. Two methods are also developed for tracking the articulation of a satellite in real-time given an articulated model using both tracked feature points and image silhouettes. Performance is evaluated for multiple inspection routes and the effect of inspection route noise is assessed. Additionally, a …
Three-Dimensional Wall Effects In A Scramjet Cavity Flameholder, Evan P. Oren
Three-Dimensional Wall Effects In A Scramjet Cavity Flameholder, Evan P. Oren
Theses and Dissertations
Scramjets, or supersonic combustion ramjets, are a key component for the development of powered hypersonic vehicles. The flameholding strategy used in this engine creates a recirculation region by creating a cavity in one side of the combustor. This highly unsteady region is difficult to interrogate through conventional means. A novel optical observation technique called hyperspectral imaging has been developed to examine the scramjet combustion chamber. The hyperspectral camera is capable of generating an interferogram at hundreds to thousands of wavelengths. These data are integrated across the line-of-sight with no information on three-dimensional (3D) location of origin. A model must be …
Investigation Of A Pressure Wave Supercharger For An Industrial Diesel Engine, Brian A. Beasley
Investigation Of A Pressure Wave Supercharger For An Industrial Diesel Engine, Brian A. Beasley
Theses and Dissertations
Internal combustion engines suffer from decreased performance as altitude is in- creased. This performance decrease can be overcome by increasing the pressure in the engine's intake manifold. Typically, this is accomplished with a turbocharger or supercharger. However, mechanical compression devices such as these suffer from decrease compression efficiency as the size of the device decreases. The size of the compression device scales with the amount of mass ow through the device, and the amount of mass ow is proportional to the size of the engine. This means a small turbocharger for a small engine is less efficient than a larger …
Thermochemical Non-Equilibrium Models For Weakly Ionized Hypersonic Flows With Application To Slender-Body Wakes, Matthew P. Clarey
Thermochemical Non-Equilibrium Models For Weakly Ionized Hypersonic Flows With Application To Slender-Body Wakes, Matthew P. Clarey
Theses and Dissertations
The current resurgence of interest in hypersonic technologies has warranted an inquiry into the commonly employed thermochemical non-equilibrium models within computational fluid dynamic (CFD) simulations. Additionally, research has historically focused on forebody flowfields, while studies of the complex wake structure have remained elusive. Although the forebody is of significance for vehicle analysis, the wake presents many exploitative characteristics. This dissertation aimed to address these two deficits. First, two three-temperature non-equilibrium models were developed, increasing the fidelity of hypersonic solutions above that of the legacy two-temperature model. The models were then investigated via zero-dimensional simulations, to detail the non-equilibrium processes, and …
Simplex Control Methods For Robust Convergence Of Small Unmanned Aircraft Flight Trajectories In The Constrained Urban Environment, Michael D. Zollars
Simplex Control Methods For Robust Convergence Of Small Unmanned Aircraft Flight Trajectories In The Constrained Urban Environment, Michael D. Zollars
Theses and Dissertations
Constrained optimal control problems for Small Unmanned Aircraft Systems (SUAS) have long suffered from excessive computation times caused by a combination of constraint modeling techniques, the quality of the initial path solution provided to the optimal control solver, and improperly defining the bounds on system state variables, ultimately preventing implementation into real-time, on-board systems. In this research, a new hybrid approach is examined for real-time path planning of SUAS. During autonomous flight, a SUAS is tasked to traverse from one target region to a second target region while avoiding hard constraints consisting of building structures of an urban environment. Feasible …
Optimal Finite Thrust Guidance Methods For Constrained Satellite Proximity Operations Inspection Maneuvers, Eric R. Prince
Optimal Finite Thrust Guidance Methods For Constrained Satellite Proximity Operations Inspection Maneuvers, Eric R. Prince
Theses and Dissertations
Algorithms are developed to find optimal guidance for an inspector satellite operating nearby a resident space object (RSO). For a non-maneuvering RSO, methods are first developed for a satellite subject to maximum slew rates to conduct an initial inspection of an RSO, where the control variables include the throttle level and direction of the thrust. Second, methods are developed to optimally maneuver a satellite with on/off thrusters into a natural motion circumnavigation or teardrop trajectory, subject to lighting and collision constraints. It is shown that for on/off thrusters, a control sequence can be parameterized to a relatively small amount of …
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 1100°C In Air And In Silicic Acid-Saturated Steam, Logan M. Gumucio
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 1100°C In Air And In Silicic Acid-Saturated Steam, Logan M. Gumucio
Theses and Dissertations
Innovations in SiC based ceramic matrix composites (CMCs) have yielded exceptional high-temperature properties and performance in aggressive oxidizing environments. These material characteristics provide potential avenues for future advancements in many applications where current metallic alloys perform near their operating temperature limits in a harsh environment. As steam (typically present in these environments) enters through cracks in the matrix of a SiC/SiC composite, it leaches Si and becomes saturated with silicic acid, Si(OH)4, prior to attacking the reinforcing SiC fibers. Therefore, it is paramount that a thorough understanding of the performance and durability of SiC fibers be obtained under …
Mitigating Interference With Knowledge-Aided Subarray Pattern Synthesis And Space Time Adaptive Processing, Yongjun Yoon
Mitigating Interference With Knowledge-Aided Subarray Pattern Synthesis And Space Time Adaptive Processing, Yongjun Yoon
Theses and Dissertations
Phased arrays are essential to airborne ground moving target indication (GMTI), as they measure the spatial angle-of-arrival of the target, clutter, and interference signals. The spatial and Doppler (temporal) frequency is utilized by space-time adaptive processing (STAP) to separate and filter out the interference from the moving target returns. Achieving acceptable airborne GMTI performance often requires fairly large arrays, but the size, weight and power (SWAP) requirements, cost and complexity considerations often result in the use of subarrays. This yields an acceptable balance between cost and performance while lowering the system’s robustness to interference. This thesis proposes the use of …
Passive Load Testing For Evaluation Of Electromechanical Actuators, Jeremiah R. Hoffman
Passive Load Testing For Evaluation Of Electromechanical Actuators, Jeremiah R. Hoffman
Theses and Dissertations
While aircraft control surfaces traditionally use hydraulic actuators, electromechanical actuators (EMAs) are interesting as they have potential to be lighter, lower maintenance, and more robust. However, EMAs require more research regarding force-fight characteristics, power requirements, performance specifications, and more. The Air Force Research Laboratory is conducting some of this research, and operates a test rig which provides a passive load to a pair of EMAs. This rig is designed for simple test profiles for investigating force-fight; if it could be used to represent actual flight profiles, the rig could accommodate a wider variety of tests. The focus of this project …
Creep Of Hafnium Diboride -20 Vol% Silicon Carbide At 1500°C In Air, Glen E. Pry
Creep Of Hafnium Diboride -20 Vol% Silicon Carbide At 1500°C In Air, Glen E. Pry
Theses and Dissertations
Refractory metal borides, commonly referred to as Ultra High Temperature Ceramics (UHTCs), exhibit a number of unique properties, such as extremely high melting temperature and hardness, chemical stability, high electrical and thermal conductivity and corrosion resistance. It has been demonstrated that the addition of SiC improves the oxidation resistance of ZrB2- and HfB2-based UHTCs above 1200°C by modifying the composition of the oxide scale. Addition of SiC retards the oxidation rate of ZrB2 and HfB2 by forming a protective layer of borosilicate glass. Creep deformation is one of the critical criterion for structural application of ceramics at elevated temperatures. Compression …
Tensile Properties And Fatigue Behavior Of Geopolymer Matrix Composites With Carbon Fiber Reinforcement At Elevated Temperature, Steffan M.L. Wilcox
Tensile Properties And Fatigue Behavior Of Geopolymer Matrix Composites With Carbon Fiber Reinforcement At Elevated Temperature, Steffan M.L. Wilcox
Theses and Dissertations
The tensile stress-strain and tension-tension fatigue of geopolymer matrix composites reinforced with 0/90 carbon fibers was investigated at 23 and 300°C in laboratory air. Geopolymers are inorganic polymeric materials composed of alumina, silica, and alkali metal oxides. Because geopolymers are synthesized as a fluid mixture or particles and liquid, they can be cast into a desired shape, and cured at only slightly elevated temperatures. The relative ease of synthesis and low processing temperatures make geopolymers an attractive choice as a matrix material for composite materials. Geopolymers also offer resistance to heat and oxidizing environments. Currently, geopolymer matrix composites are being …
Stereo Vision: A Comparison Of Synthetic Imagery Vs. Real World Imagery For The Automated Aerial Refueling Problem, Nicholas J. Seydel
Stereo Vision: A Comparison Of Synthetic Imagery Vs. Real World Imagery For The Automated Aerial Refueling Problem, Nicholas J. Seydel
Theses and Dissertations
Missions using unmanned aerial vehicles have increased in the past decade. Currently, there is no way to refuel these aircraft. Accomplishing automated aerial refueling can be made possible using the stereo vision system on a tanker. Real world experiments for the automated aerial refueling problem are expensive and time consuming. Currently, simulations performed in a virtual world have shown promising results using computer vision. It is possible to use the virtual world as a substitute environment for the real world. This research compares the performance of stereo vision algorithms on synthetic and real world imagery.
Stabilized Rpa Flight In Building Proximity Operations, Michael M. Kaniut
Stabilized Rpa Flight In Building Proximity Operations, Michael M. Kaniut
Theses and Dissertations
The thesis seeks a solution to the requirement for a highly reliable and capable Unmanned Air Vehicle (UAV) to support a wide array of missions and applications that require close proximity flight to structures. The scope of the project includes the drafting of a concept of operations (CONOPs) describing how the mission requirements might be met using the sensor, operators, and air vehicle described here in. The demonstration of the wall-following section of that CONOPs is performed by cart testing a custom algorithm and evaluating its ability to react to its environment. Finally, a flight test was performed to characterize …
Creep Of Nextel 720/A Ceramic Matrix Composite With Laser Drilled Effusion Holes At 1200°C In Air And In Steam, Savannah N. Minor
Creep Of Nextel 720/A Ceramic Matrix Composite With Laser Drilled Effusion Holes At 1200°C In Air And In Steam, Savannah N. Minor
Theses and Dissertations
Creep behavior of an oxide-oxide ceramic matrix composite (CMC) containing an array of effusion holes was investigated at 1200⁰C in air and in steam. The composite (N720/A) consisted of a porous alumina matrix reinforced with alumina-mullite NextelTM 720 fibers. Test specimens had an array of 17 effusion holes with 0.5-mm diameter. The effusion holes were drilled through the specimen thickness normal to the specimen surface using a CO2 laser. Effect of the effusion holes on tensile properties was evaluated tension tests to failure at 1200°C in air. Creep of specimens with effusion holes at 1200°C was studied for creep stresses …
Behavior Flexibility For Autonomous Unmanned Aerial Systems, Taylor B. Bodin
Behavior Flexibility For Autonomous Unmanned Aerial Systems, Taylor B. Bodin
Theses and Dissertations
Autonomous unmanned aerial systems (UAS) could supplement and eventually subsume a substantial portion of the mission set currently executed by remote pilots, making UAS more robust, responsive, and numerous than permitted by teleoperation alone. Unfortunately, the development of robust autonomous systems is difficult, costly, and time-consuming. Furthermore, the resulting systems often make little reuse of proven software components and offer limited adaptability for new tasks. This work presents a development platform for UAS which promotes behavioral flexibility. The platform incorporates the Unified Behavior Framework (a modular, extensible autonomy framework), the Robotic Operating System (a RSF), and PX4 (an open- source …
Modeling A Space-Based Quantum Link, Alexander W. Duchane
Modeling A Space-Based Quantum Link, Alexander W. Duchane
Theses and Dissertations
Quantum sources and single photon detectors have improved, allowing quantum algorithms for communication, encryption, computing, and sensing to transition from theory and small-scale laboratory experiments to field experiments. One such quantum algorithm, Quantum Key Distribution, uses optical pulses to generate shared random bit strings between two locations. These shared bit strings can be turned into encryption keys to be used as a one-time-pad or integrated with symmetric encryption techniques such as the Advanced Encryption Standard. This method of key generation and encryption is resistant to future advances in quantum computing which significantly degrade the effectiveness of current asymmetric key sharing …
Military Application Of Aerial Photogrammetry Mapping Assisted By Small Unmanned Air Vehicles, Kijun Lee
Military Application Of Aerial Photogrammetry Mapping Assisted By Small Unmanned Air Vehicles, Kijun Lee
Theses and Dissertations
This research investigated the practical military applications of the photogrammetric methods using remote sensing assisted by small unmanned aerial vehicles (SUAVs). The research explored the feasibility of UAV aerial mapping in terms of the specific military purposes, focusing on the geolocational and measurement accuracy of the digital models, and image processing time. The research method involved experimental flight tests using low-cost Commercial off-the-shelf (COTS) components, sensors and image processing tools to study key features of the method required in military like location accuracy, time estimation, and measurement capability. Based on the results of the data analysis, two military applications are …
Effects Of Manufacturing Process Variables On Ultrasonic Testing In Electron Beam Melted Ti-6al-4v, Andrew D. Durkee
Effects Of Manufacturing Process Variables On Ultrasonic Testing In Electron Beam Melted Ti-6al-4v, Andrew D. Durkee
Theses and Dissertations
Further research on validating additive manufacturing production quality is required before the realization of direct print-to-fly application of critical components. This research examines the response of ultrasonic testing as a function of various manufacturing variables in electron beam melted samples of Ti-6Al-4V. Four dimensionally identical blocks with 6 spherical voids at varying depths were manufactured using different combinations of stock powder, edge treatments, and void melting. Scans were completed on two sides of each specimen with the transducer focused on the mid-plane. Additionally, one specimen was scanned 6 times, with the focal plane adjusted for each scan to match the …
Design And Test Of A Uav Swarm Architecture Over A Mesh Ad-Hoc Network, Timothy J. Allen
Design And Test Of A Uav Swarm Architecture Over A Mesh Ad-Hoc Network, Timothy J. Allen
Theses and Dissertations
The purpose of this research was to develop a testable swarm architecture such that the swarm of UAVs collaborate as a team rather than acting as several independent vehicles. Commercial-off-the-shelf (COTS) components were used as they were low-cost, readily available, and previously proven to work with at least two networked UAVs. Initial testing was performed via software-in-the-loop (SITL) demonstrating swarming of three simulated multirotor aircraft, then transitioned to real hardware. The architecture was then tested in an outdoor nylon netting enclosure. Command and control (C2) was provided by software implementing an enhanced version of Reynolds’ flocking rules via an onboard …
Design, Buildup, And Testing Of A Radial Rotating Detonation Engine For A Compact Auxiliary Power Unit, Riley Huff
Design, Buildup, And Testing Of A Radial Rotating Detonation Engine For A Compact Auxiliary Power Unit, Riley Huff
Theses and Dissertations
Current power generators consume a large portion of the aircrafts usable volume and they are also extremely heavy for the amount of power that they can produce. Therefore, a need for compact, lightweight Auxiliary Power Units (APU) with high power density has arisen. A novel solution to this problem comes in the form of coupling a Rotating Detonation Engine (RDE) with a turbine generator. A new type of RDE referred to as the Radial Rotating Detonation Engine (RRDE) has been developed to fill this need. This project marks the first radial ow RDE successfully operated in the United States, and …
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Theses and Dissertations
The direct simulation of turbulent flows is prohibitive at high Reynolds numbers; thus, methods such as RANS and LES are used. However, these methods still require a large number of cells near a solid boundary. To circumvent this issue, a Wall-Modeled Large Eddy Simulation (WM-LES) can be used. Of interest is how these wall models perform in comparison to a Wall-Resolved Large Eddy Simulation (WR-LES) and experimental results of a shock turbulent boundary layer interactions (STBLI) and specifically, whether equilibrium wall models are sufficient to resolve the oscillatory and hence non-equilibrium nature of these flows or whether a non-equilibrium model …
Design And Testing Of An Additively Manufactured Cubesat Structural Bus, Karson A. Roberts
Design And Testing Of An Additively Manufactured Cubesat Structural Bus, Karson A. Roberts
Theses and Dissertations
Recent innovations in additive manufacturing and design capabilities have opened the door for more opportunities to integrate multiple functions into a structural de- sign. Specifically, 3D printing through advanced laser powder bed fusion of metal powder allows for the development and integration of advanced structures that were previously unachievable. The demonstration of these techniques on a small satellite results in a structural bus consisting of various external and internal features, increasing its functionality and capabilities beyond simply providing structural support. 3D printing a multi-functional CubeSat bus with these integrated features such as internal lattices and wiring tabs demonstrates a new …
Investigation Of Geometric And Thermal Scaling Effects On Simulated Turbine Vane Leading Edge Model, James G. Tewaheftewa
Investigation Of Geometric And Thermal Scaling Effects On Simulated Turbine Vane Leading Edge Model, James G. Tewaheftewa
Theses and Dissertations
Film cooling is still a bustling research topic, especially with burgeoning manufacturing techniques on the horizon that will open the design space. However, despite the number of years that have gone into gas turbine design and research, evaluating cooling performance on components still presents challenges. This task becomes especially difficult and dangerous if trying to do so in realistic engine conditions. Therefore, the majority of film cooling research is performed at conditions far from realistic engine conditions, often using materials that would never hold up to turbine inlet temperature, and scaled to predict results at engine conditions. Previous film cooling …