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Articles 691 - 720 of 1780
Full-Text Articles in Aerospace Engineering
Computational Simulation Of Explosively Generated Pulsed Power Devices, Mollie C. Drumm
Computational Simulation Of Explosively Generated Pulsed Power Devices, Mollie C. Drumm
Theses and Dissertations
Technology and size constraints have limited the development of the end game mechanisms of today's modern military weapons. A smaller, more efficient means of powering these devices is needed, and explosive pulsed power devices could be that answer. While most prior research has been in the experimental field, there is a need for more theory-based research and a computer modeling capability. The objective of this research was to use experimental data collected by the US Army at Redstone Arsenal from their ferroelectric generator (FEG) design in combination with the ALEGRA-EMMA code to develop a computer model that can accurately represent …
Feasibility Analysis On The Utilization Of The Iridium Satellite Communications Network For Resident Space Objects In Low Earth Orbit, John R. Claybrook
Feasibility Analysis On The Utilization Of The Iridium Satellite Communications Network For Resident Space Objects In Low Earth Orbit, John R. Claybrook
Theses and Dissertations
In recent years, space has become more congested and contested, particularly in low Earth orbit (LEO), generating the need for a low-latency capability to provide precise orbital knowledge and accurate space situational awareness information. This thesis investigates the feasibility of resident space objects (RSOs) in LEO communicating continuously with ground operators or users through the Iridium Satellite Communications Network. Due to the problem's complexity and required time for computation, a test-industry technique called Design of Experiments is implemented in order to efficiently study the feasibility of the communication link. Specifically, an optimal response surface method is chosen to design the …
Using Hysteretic Energy To Evaluate Damping Characteristics Of Hard Coating On Titanium, Colin C. Engebretsen
Using Hysteretic Energy To Evaluate Damping Characteristics Of Hard Coating On Titanium, Colin C. Engebretsen
Theses and Dissertations
Current methods of material damping evaluation consist of bending tests involving half-power bandwidth base excitation or free decay methods measured by laser vibrometer. These methods are accompanied by complex, nonlinear strain evaluation; they are vulnerable to undesired air damping; and they require less than commonplace equipment. The measurement of hysteretic energy loss in axial cyclic loading alleviates these difficulties. By using common tensile testing machines, strain is kept linear and air damping is of no concern. Furthermore, the static test section allows for simplified environmental variation for high temperature or high humidity testing. This study set forth to advance and …
Application Of Finite Element To Evaluate Material With Small Modulus Of Elasticity, Boyce H. Dauby
Application Of Finite Element To Evaluate Material With Small Modulus Of Elasticity, Boyce H. Dauby
Theses and Dissertations
This thesis describes the development of a series of models utilizing the commercial finite element suite ABAQUS specifically to apply towards the study of biological tissue. The end goal is to be able to obtain the material properties of the Manducca Sexta, a biological inspiration for flapping wing micro-air vehicles. Two finite element models were used to analyze the results of two prior studies of other researchers. A flat punch elastic model examined boundary effects and confirmed that the point of indentation was far enough removed from the boundary. The hyperelastic spherical indentation experiment examined the effects of coefficient of …
Biaxial (Tension-Torsion) Testing Of An Oxide/Oxide Ceramic Matrix Composite, Joseph M. Derienzo
Biaxial (Tension-Torsion) Testing Of An Oxide/Oxide Ceramic Matrix Composite, Joseph M. Derienzo
Theses and Dissertations
High temperatures and structural loads in advanced aerospace structures often result in complex loading conditions. This study is focused on biaxial (tension-torsion) testing of an oxide-oxide porous matrix ceramic matrix composite (CMC) (NextelTM 720/AS) thin wall tube with a novel involute layup. Tests included pure torsion and biaxial (tension- torsion) loading. Strain gages were used in addition to digital image correlation (DIC) to measure strains and to detect crack initiation and propagation. Room temperature and 1100°C uniaxial tests were performed in a build up approach prior to biaxial (tension-torsion) testing. Double-notch shear (DNS) specimens were tested at 1100°C in air …
Integration Of An Inter Turbine Burner To A Jet Turbine Engine, Matthew M. Conrad
Integration Of An Inter Turbine Burner To A Jet Turbine Engine, Matthew M. Conrad
Theses and Dissertations
As aircraft power requirements continue to grow, whether for electrical systems or increased thrust, improved engine efficiency must be found. An Ultra-Compact Combustor (UCC) is a proposed apparatus for accomplishing this task by burning in the circumferential direction as a main combustor or an Inter-Turbine Burner (ITB). In order for the UCC to be viable it is important to study the effects of feeding the core and circumferential flows from a common gas reservoir. This research effort has developed a diffuser, for the AFIT Combustion Laboratory, that is capable of 80/20, 70/30, and 60/40 mass flow splits between the core …
Dynamic Constellation Tasking And Management, Steven P. Ingraham
Dynamic Constellation Tasking And Management, Steven P. Ingraham
Theses and Dissertations
Responsive orbits have gained much attention in recent years and many AFIT theses have addressed this topic. Specifically, the following topics have been studied: phasing within an orbit, adjusting time of arrival, avoidance, and maneuver detection. This thesis seeks to determine the feasibility of maneuvering satellites from circular (600 km) orbits to eccentric (600 km by 175 km) orbits in order to collect high resolution images for Earth surveillance. Coverage is calculated for multiple 6-satellite constellations. Perturbations for the subject orbits are analyzed and compared to simulation results.
Effects Of Temperature On The Performance Of A Small Internal Combustion Engine At Altitude, Travis D. Husaboe
Effects Of Temperature On The Performance Of A Small Internal Combustion Engine At Altitude, Travis D. Husaboe
Theses and Dissertations
The effects of atmospheric pressure and temperature variations on the performance of small internal combustion (IC) engines operating at altitudes significantly above sea level are not widely documented. Using an altitude chamber and fuel-injected twostroke engine, data were collected while varying air temperature along with pressure. The peak engine power was 4.1 kW at roughly sea level standard conditions and dropped to 3.5 kW at the standard conditions for an altitude of 1.5 km. At a combination of pressure and temperature corresponding to an altitude of 3 km, peak power fell further to 2.5 kW. The combined effects of standard …
A Study Of The Thermal Environment Developed By A Traveling Slipper At High Velocity, Kathleen H. Le
A Study Of The Thermal Environment Developed By A Traveling Slipper At High Velocity, Kathleen H. Le
Theses and Dissertations
The research presented in this thesis is developed from the relative sliding motion of a traveling slipper and stationary rail at the Holloman High Speed Test Track located at Holloman AFB, NM. The high velocity condition of the slipper traveling down the rail creates a thermal environment that is of interest to the researchers at the Air Force Institute of Technology. The high temperatures coupled with high velocity leads to a non-linear problem known as melt wear. The goal of this research is to characterize the amount of heat flow going into the slipper as it traverses the rail and …
Development Of Optimized Piezoelectric Bending Actuators For Use In An Insect Sized Flapping Wing Micro Air Vehicle, Robert K. Lenzen
Development Of Optimized Piezoelectric Bending Actuators For Use In An Insect Sized Flapping Wing Micro Air Vehicle, Robert K. Lenzen
Theses and Dissertations
Piezoelectric bimorph actuators, as opposed to rotary electric motors, have been suggested as an actuation mechanism for flapping wing micro air vehicles (FWMAVs) because they exhibit favorable characteristics such as low weight, rapidly adaptable frequencies, lower acoustic signature, and controllable flapping amplitudes. Research at the Air Force Research Labs and the Air Force Institute of Technology has shown that by using one actuator per wing, up to five degrees of freedom are possible. However, due to the weight constraints on a FWMAV, the piezoelectric bimorph actuators need to be fully optimized to support free flight. This study focused on three …
Finite Element Analysis Of A Highly Flexible Flapping Wing, Justin K. Mason
Finite Element Analysis Of A Highly Flexible Flapping Wing, Justin K. Mason
Theses and Dissertations
Small unmanned aerial systems are being designed to emulate the flapping kinematics of insects and birds which show superior control in slow speed regimes compared to fixed wing or rotorcraft aircraft. The flight of flapping wing vehicles is characterized by aeroelastic effects. Most research has been dedicated towards understanding the aerodynamic side of the aeroelastic response with minimal effort spent towards validating the structural response. A finite element model of a wing from a commercial flapping wing vehicle was created to validate the structural response. Vacuum testing allowed the isolation of the inertial response for a direct comparison to the …
Experimental Characterization Of The Structural Dynamics And Aero-Structural Sensitivity Of A Hawkmoth Wing Toward The Development Of Design Rules For Flapping Wing Micro Air Vehicles, Aaron G. Norris
Theses and Dissertations
A case is made for why the structures discipline must take on a more central role in the research and design of flapping-wing micro-air-vehicles, especially if research trends continue toward bio-inspired, insect-sized flexible wing designs. In making the case, the eigenstructure of the wing emerges as a key structural metric for consideration. But with virtually no structural dynamic data available for actual insect wings, both engineered and computational wing models that have been inspired by biological analogs have no structural truth models to which they can be anchored. An experimental framework is therefore developed herein for performing system identification testing …
Heat Exchanger Design And Testing For A 6-Inch Rotating Detonation Engine, Scott W. Theuerkauf
Heat Exchanger Design And Testing For A 6-Inch Rotating Detonation Engine, Scott W. Theuerkauf
Theses and Dissertations
This thesis explains the design and testing of a water-cooled rotating detonation engine (RDE) run on hydrogen and air. The change in water temperature as it cooled the engine was used to find the steady heat rate into the containing walls of the detonation channel. The engine successfully ran four times for 20 seconds each. The steady-state heat rate was measured to be 2.5% of the propellant lower heating value (LHV) into the outer wall and 7.1% of LHV into the inner wall. Additionally, a quick-response resistance temperature detector (RTD) was used in an uncooled RDE of similar dimension to …
Experimental Analysis Of Dampened Breathing Mode Oscillation On Hall Effect Thruster Performance, Christopher D. Vineski
Experimental Analysis Of Dampened Breathing Mode Oscillation On Hall Effect Thruster Performance, Christopher D. Vineski
Theses and Dissertations
Experiments were performed at AFIT to determine the effect of active control of the magnetic field strength to reduce the breathing mode oscillation on the efficiency of a 200W Hall thruster. The breathing mode oscillation amplitude was measured by the root mean square (RMS) variation in the AC portion of the discharge current. Experiments were run using krypton and xenon propellant. Using the xenon propellant control of the RMS improved the propellant utilization efficiency by approximately 2% in two cases, while reducing the magnet current efficiency by about 10%. Control of the RMS's effect on the divergence angle of the …
Training Maneuver Evaluation For Reduced Order Modeling Of Stability & Control Properties Using Computational Fluid Dynamics, Craig C. Porter
Training Maneuver Evaluation For Reduced Order Modeling Of Stability & Control Properties Using Computational Fluid Dynamics, Craig C. Porter
Theses and Dissertations
System identification has long been used as a tool for flight test engineers to characterize systems under test; however, the inputs to these characterization activities have previously been limited to wind tunnel and flight test data. There has been a recent effort to incorporate computational fluid dynamics (CFD) into the system identification process. An integral piece of the process is the simulation of training maneuvers utilizing CFD. Up until now, the suitability of particular training maneuvers has been assessed by comparing the reduced model to known results. This research strives to recommend a set of parameters to be used in …
High Frequency Magnetic Field Direction Finding Using Mgl-S8a B-Dot Sensors, Michael D. Archer
High Frequency Magnetic Field Direction Finding Using Mgl-S8a B-Dot Sensors, Michael D. Archer
Theses and Dissertations
Aircraft based direction finding (DF) in the high frequency (HF) band is difficult due to the aircraft's size with respect to wavelength and limited azimuthal resolution. A B-dot sensor is useful for detection of the time varying magnetic field and offers improved integration into an aircraft. What the B-dot sensor gains in integration it gives up in sensitivity because it is designed for frequencies above 5 GHz. Design of an airborne HFDF array using Bdot sensors is based in maximizing the physical extent of the array and eliminating multiple main beams. The goals of this research are to complete a …
Porous Emitter Colloid Thruster Performance Characterization Using Optical Techniques, Eric T. Wolf
Porous Emitter Colloid Thruster Performance Characterization Using Optical Techniques, Eric T. Wolf
Theses and Dissertations
This research focuses on experimentally characterizing the performance parameters of a colloid thruster with porous emitters through optical techniques. Porous emitters are different than traditional needle emitters in how they allow a variation in the number and size of Taylor Cones throughout a range of propellant volumetric flow rate conditions. An algorithm is created to calculate the estimated minimum and maximum number of emitter sites based on magnified images of the porous emitter heads. Theoretical thruster performance parameters are then established from the estimated number of emitter sites. Experimental techniques for measuring the thrust and exhaust exit velocity are proposed. …
Creep Of Hi-Nicalon S Fiber Tows At Elevated Temperature In Air And In Steam, Theodore R. Shillig
Creep Of Hi-Nicalon S Fiber Tows At Elevated Temperature In Air And In Steam, Theodore R. Shillig
Theses and Dissertations
Structural aerospace components require materials that have superior long-term mechanical properties and can withstand severe environmental conditions, such as high temperatures, high pressures and moisture. Ceramic-matrix composites (CMCs) are capable of maintaining excellent strength and creep resistance at high temperatures, which makes them attractive candidate materials for aerospace applications, particularly in propulsion components. Silicon Carbide (SiC) ceramic fibers have been used as constituent materials in CMCs, although oxidation of the SiC to SiO2 has been a known fiber degradation mechanism. Recently developed near stoichiometric Hi-Nicalon-S fibers have shown significant improvements in thermo-chemical stability. Creep of the Hi-Nicalon-S fibers at elevated …
Real-Time Heading Estimation Using Perspective Features, James W. Dean
Real-Time Heading Estimation Using Perspective Features, James W. Dean
Theses and Dissertations
There are a large number of commercially available quad-rotor helicopters available from various manufacturers. All of these systems rely on a low cost MEMS based inertial measurement system for stabilization and navigation. These low cost inertial systems are all subject to rapid error growth in their attitude and position estimates unless bounded by external measurements. This thesis created real-time algorithm to integrate measurements from visual cues with measurements from onboard sensors to estimate the attitude position and velocity of a quad-rotor helicopter in a local navigation frame, a system model for the ARDrone, and a feed-back controller for the vehicle's …
Information Encoding On A Pseudo Random Noise Radar Waveform, Joshua A . Hardin
Information Encoding On A Pseudo Random Noise Radar Waveform, Joshua A . Hardin
Theses and Dissertations
Navigation requires knowledge of current location and a planned destination. This is true with manned vehicles and unmanned vehicles. There are many ways to acquire the current location, including global positioning system (GPS), triangulation, radar, and dead reckoning. Today GPS is the most reliable and accurate navigation technique when there is a clear, unobstructed view of the satellite constellation. Various sensors can be used to perform indoor navigation; however, when the vehicle is autonomous the sensors need to provide the exact location to the system. This research determined if using a template replay strategy has the same RNR performance as …
Error Characterization Of Vision-Aided Navigation Systems, Daniel A . Marietta
Error Characterization Of Vision-Aided Navigation Systems, Daniel A . Marietta
Theses and Dissertations
The goal of this work is to characterize the errors committed by an Image Aided Navigation (IAN) algorithm that has been developed for use as a navigation tool in GPS denied areas. The filter under study was developed by the Air Force Institute of Technology's Advanced Navigation Technology center, and has been the focus of numerous research efforts. Unfortunately, these studies have all been based on single runs or simulations, and such results may not be indicative of the true filter performance. This problem extends to IAN publications in general; no analysis of IAN based upon a sizable real world …
Inertial Navigation System Aiding Using Vision, James O. Quarmyne
Inertial Navigation System Aiding Using Vision, James O. Quarmyne
Theses and Dissertations
The aiding of an INS using measurements over time of the line of sight of ground features as they come into view of an onboard camera is investigated. The objective is to quantify the reduction in the navigation states' errors by using bearings-only measurements over time of terrain features in the aircraft's field of view. INS aiding is achieved through the use of a Kalman Filter. The design of the Kalman Filter is presented and it is shown that during a long range, wings level cruising flight at constant velocity and altitude, a 90% reduction in the aided INS-calculated navigation …
Adaptations And Analysis Of The Afit Noise Radar Network For Indoor Navigation, Russell D. Wilson Iv
Adaptations And Analysis Of The Afit Noise Radar Network For Indoor Navigation, Russell D. Wilson Iv
Theses and Dissertations
After several years of development, the AFIT Noise Radar Network (NoNET) has proven to be an extremely versatile system for many standard radar functions. This pallet of capabilities includes through the wall target tracking capabilities due to its wide bandwidth and UHF operations. Utilizing White Gaussian Noise as its waveform, the NoNET can operate at much lower power levels than other comparable systems while remaining extremely covert. In an effort to explore new applications, the question arose could the NoNET provide a viable option for navigation capability in GPS denied and indoor environments? This research aims to provide proof of …
Pseudolite Architecture And Performance Analysis For The Faa's Nextgen Airspace, Joseph A . Czabaranek
Pseudolite Architecture And Performance Analysis For The Faa's Nextgen Airspace, Joseph A . Czabaranek
Theses and Dissertations
By 2025 the FAA plans to have fully implemented its NextGen Airspace design. NextGen takes advantage of modern positioning technologies as well as automation, data sharing, and display technologies that will allow more efficient use of our ever busier National Airspace (NAS). A key element of NextGen is the transition from surveillance RADAR providing aircraft separation and navigation to the use of the GPS and Automatic Dependent Surveillance Broadcast (ADS-B). ADS-B couples the precision of the GPS with networked ground and airborne receivers to provide precise situational awareness to pilots and controllers. The result is increased safety, capacity, and access …
Effects Of Stereoscopic 3d Digital Radar Displays On Air Traffic Controller Performance, Jason G. Russi
Effects Of Stereoscopic 3d Digital Radar Displays On Air Traffic Controller Performance, Jason G. Russi
Theses and Dissertations
Air traffic controllers are responsible for directing air traffic based upon decisions made from traffic activity depicted on 2Dimensional (2D) radar displays. Controllers must identify aircraft and detect potential conflicts while simultaneously developing and executing plans of action to ensure safe separation is maintained. With a nearly 100% increase in traffic expected within the next decade (FAA, 2012a), controllers' abilities to rapidly interpret spacing and maintain awareness for longer durations with increased workload will become increasingly imperative to safety. The current display design spatially depicts an aircraft's position relative to the controller's airspace as well as speed, altitude, and direction …
Supplementary Computer Generated Cueing To Enhance Air Traffic Controller Efficiency, Laurienne Cibelle Rodrigues De Assis Santana
Supplementary Computer Generated Cueing To Enhance Air Traffic Controller Efficiency, Laurienne Cibelle Rodrigues De Assis Santana
Theses and Dissertations
Air traffic controllers are often required to simultaneously communicate with several aircraft over multiple radio frequencies. As a result, during peak loading, it is common for the controller to receive multiple concurrent communications, each from a different aircraft, making it difficult to discern audio messages received from multiple pilots simultaneously. To address this problem, a modified air traffic control (ATC) interface was prototyped with the goal of increasing controller-to-pilot communication efficiency. This prototype included supplementary text cueing which was provided by a hypothetical automated text to speech system in an on-screen text box for controller reference in the event of …
Development Of Autonomous Optimal Cooperative Control In Relay Rover Configured Small Unmanned Aerial Systems, Timothy J. Shuck
Development Of Autonomous Optimal Cooperative Control In Relay Rover Configured Small Unmanned Aerial Systems, Timothy J. Shuck
Theses and Dissertations
This thesis documents the research effort to develop, integrate and implement the system hardware and the software necessary to validate the Air Force Institute of Technology's theoretical advances in small unmanned aerial systems (SUAS) cooperative control. The end state objective of the research effort was to flight test an autonomous control algorithm on a communication relay unmanned aerial vehicle (UAV) that was actively relaying data to and from a rover UAV. The relay UAV is one part of a SUAS designed to utilize cooperative control to extend the effective line-of-sight operating range for a rover UAV. An algorithm is integrated …
Aerial Networking For The Implementation Of Cooperative Control On Small Unmanned Aerial Systems, Scott A . Songer
Aerial Networking For The Implementation Of Cooperative Control On Small Unmanned Aerial Systems, Scott A . Songer
Theses and Dissertations
The employment of Small Unmanned Aerial Systems (SUAS) for reconnaissance and surveillance missions is a vital capability of the United States military. Cooperative control algorithms for SUAS can enable tactical multi-vehicle configurations for communications extension, intelligent navigation, and a multitude of other applications. Past research at AFIT has designed and simulated a cooperative rover-relay algorithm for extended communications and has investigated its implementation through various modem configurations. This research explores aerial networking options for implementing cooperative control and applies them to an actual SUAS. Using Commercial Off-The-Shelf (COTS) hardware, a system was designed and flight tested to implement the rover-relay …
Design Of A Control Moment Gyroscope Attitude Actuation System For The Attitude Control Subsystem Proving Ground, Samuel C. Johnson
Design Of A Control Moment Gyroscope Attitude Actuation System For The Attitude Control Subsystem Proving Ground, Samuel C. Johnson
Theses and Dissertations
All spacecraft represent a considerable investment of both time and money. To ensure mission success, testing and validation of all vital systems is crucial to the design process. The attitude control subsystem (ACS) is typically tested thoroughly, to include both hardware and control algorithms. Computer simulations offer a simple and relatively cheap method of predicting the performance of the ACS; however, computer simulations cannot provide the assurances necessary to qualify an ACS hardware configuration or control algorithm spaceworthy. For this reason, physical spacecraft simulators must be used to validate ACS dynamics. Previous research showed there is room for significant improvement …
Film Cooling In Fuel Rich Environments, Jacob J. Robertson
Film Cooling In Fuel Rich Environments, Jacob J. Robertson
Theses and Dissertations
The ultra compact combustor is a high performance gas turbine design concept that portends reduced weight for future weapons platforms. A natural outcome of the design is the continual presence of fuel-rich air in the turbine component of the engine. Because modern cooling schemes for hot section turbine blades involve injecting cool, oxygen-rich air adjacent to the surface, the potential arises for reaction with the unconsumed radicals in the mainstream ow and augmented heat transfer to the blade. This outcome is contrary to the purpose of film cooling, and can lead to early life-cycle turbine failure. This study examined the …