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Aerospace Engineering

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Articles 3061 - 3090 of 4452

Full-Text Articles in Engineering

Numerical Simulation Of A Liquid Jet Atomization And Break-Up Using Ansys-Cfx 12.0, Yash Akhil Bhatt Apr 2010

Numerical Simulation Of A Liquid Jet Atomization And Break-Up Using Ansys-Cfx 12.0, Yash Akhil Bhatt

Master's Theses - Daytona Beach

Break-up and atomization characteristics of JetA liquid fuel were investigated numerically. The results have been compared to various experimental results to evaluate the accuracy of the numerical model. The CFD code ANSYS-CFX 12.0 was used to carry out the steady state analysis at different time scales. A comparison between the atomization characteristics of a pressure jet atomizer and an air-blast atomizer is shown. By employing a Lagrangian particle tracking method to track the path of the liquid particles, the liquid jet/spray phenomena was studied in light of low and high back pressure environments. The 'BLOB' primary atomization model and the …

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Neural Network Fatigue Life Prediction In Notched Aluminum Specimens From Acoustic Emission Data, Muhammed Arif Okur Apr 2010

Neural Network Fatigue Life Prediction In Notched Aluminum Specimens From Acoustic Emission Data, Muhammed Arif Okur

Master's Theses - Daytona Beach

This purpose of this research was to identify fatigue crack growth and predict failure for 7075-T6 aluminum notched bars under uniaxial tensile loading using acoustic emission (AE) data. The experiments performed in this study extend the results obtained by previous researchers who used maximum cyclic loads of 4,000, 3,000, and 2,000 pounds at a stress ratio of R = 0.0 and a frequency of 1 Hz to perform the fatigue tests. For this research the cyclic load remained at 2,000 pounds, but an additional ten specimens were tested in order to increase the amount of AE data available to the …

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Effect Of Time Pressure And Task Uncertainty On Human Operator Performance And Workload For Autonomous Aerial Vehicle Missions, Trevor Peterson Apr 2010

Effect Of Time Pressure And Task Uncertainty On Human Operator Performance And Workload For Autonomous Aerial Vehicle Missions, Trevor Peterson

Master's Theses - Daytona Beach

Unmanned aircraft systems (UAS) are being utilized at an increasing rate for a number of military applications. The potential for their use in the national airspace is also of interest to the Federal Aviation Administration, but there are some concerns about the safety of flying unmanned aircraft. The role of a UAS operator differs from that of a pilot in a manned aircraft, and this new role creates a need for a shift in interface and task design in order to take advantage of the full potential of these systems. This study examined the effect of time pressure and task …

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Acoustic Emission Fatigue Crack Monitoring Of A Simulated Aircraft Fuselage Structure, Jeremy James Lucas Apr 2010

Acoustic Emission Fatigue Crack Monitoring Of A Simulated Aircraft Fuselage Structure, Jeremy James Lucas

Doctoral Dissertations and Master's Theses

The purpose of this research was to replicate the fatigue cracking that occurs in aircraft placed under loads from cyclical compression and decompression. As a fatigue crack grows, it releases energy in the form of acoustic emissions. These emissions are transmitted through the structure in waves, which can be recorded using acoustic emission (AE) transducers. This research employed a pressure vessel constructed out of aluminum and placed under cyclical loads at 1 Hz in order to simulate the loads placed on an aircraft fuselage in flight. The AE signals were recorded by four resonant AE transducers. These were placed on …

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Hybrid Intelligent Optimization Methods For Engineering Problems, Yasin Volkan Pehlivanoglu Apr 2010

Hybrid Intelligent Optimization Methods For Engineering Problems, Yasin Volkan Pehlivanoglu

Mechanical & Aerospace Engineering Theses & Dissertations

The purpose of optimization is to obtain the best solution under certain conditions. There are numerous optimization methods because different problems need different solution methodologies; therefore, it is difficult to construct patterns. Also mathematical modeling of a natural phenomenon is almost based on differentials. Differential equations are constructed with relative increments among the factors related to yield. Therefore, the gradients of these increments are essential to search the yield space. However, the landscape of yield is not a simple one and mostly multi-modal. Another issue is differentiability. Engineering design problems are usually nonlinear and they sometimes exhibit discontinuous derivatives for …

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High Order Finite Elements For Lagrangian Computational Fluid Dynamics, Truman Everett Ellis Apr 2010

High Order Finite Elements For Lagrangian Computational Fluid Dynamics, Truman Everett Ellis

Master's Theses

A general finite element method is presented to solve the Euler equations in a Lagrangian reference frame. This FEM framework allows for separate arbitrarily high order representation of kinematic and thermodynamic variables. An accompanying hydrodynamics code written in Matlab is presented as a test-bed to experiment with various basis function choices. A wide range of basis function pairs are postulated and a few choices are developed further, including the bi-quadratic Q2-Q1d and Q2-Q2d elements. These are compared with a corresponding pair of low order bi-linear elements, traditional Q1-Q0 and sub-zonal pressure Q1-Q1d. Several test problems are considered including static convergence …

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Assessing The V2-F Turbulence Models For Circulation Control Applications, Travis M. Storm Apr 2010

Assessing The V2-F Turbulence Models For Circulation Control Applications, Travis M. Storm

Master's Theses

In recent years, airports have experienced increasing airport congestion, partially due to the hub-and-spoke model on which airline operations are based. Current airline operations utilize large airports, focusing traffic to a small number of airports. One way to relieve such congestion is to transition to a more accessible and efficient point-to-point operation, which utilizes a large web of smaller airports. This expansion to regional airports propagates the need for next-generation low-noise aircraft with short take-off and landing capabilities. NASA has attacked this problem with a high-lift, low-noise concept dubbed the Cruise Efficient Short Take-Off and Landing (CESTOL) aircraft. The goal …

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Analysis Of Helicopter Downwash/Frigate Airwake Interaction Using Statistically Designed Experiments, Yavuz Nacakli Apr 2010

Analysis Of Helicopter Downwash/Frigate Airwake Interaction Using Statistically Designed Experiments, Yavuz Nacakli

Mechanical & Aerospace Engineering Theses & Dissertations

A research program to investigate helicopter downwash/frigate airwake interaction has been initiated using a statistically robust experimental program featuring Design of Experiments. Engineering analysis of the helicopter/frigate interface is complicated by the fact that two flowfields become inherently coupled as separation distance decreases. The final objective of this work is to develop experimental methods to determine when computer simulations need to include the effects of a coupled flowfield versus using a simplified representation by superposing the velocity fields of the individual flowfields. The work presented was performed in the Old Dominion University Low Speed Wind Tunnel using a simplified 1/50 …

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Compression Testing Of Composite Laminated Foam Under Thermal Loading And With Central Holes, Dominic Surano, Jonathan Russo, Daniel Leighton Mar 2010

Compression Testing Of Composite Laminated Foam Under Thermal Loading And With Central Holes, Dominic Surano, Jonathan Russo, Daniel Leighton

Aerospace Engineering

A study was conducted to investigate the effect of heat on composite sandwich plates, fabricated with the vacuum resin infusion process, with center holes of varying diameters. The study involved conventional notched specimens and notched specimens with shear keys, both of which were subjected to monotonic inplane compression loading. Hole diameter was be varied from one to four inches in one inch increments. Loading rate was applied using the Instron machine at one millimeter per minute. The diameter of the shear key around the holes varied from one inch to four inches in one inch increments. The specimens were placed …

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Orbit Maneuver For Responsive Coverage Using Electric Propulsion, Timothy S. Hall Mar 2010

Orbit Maneuver For Responsive Coverage Using Electric Propulsion, Timothy S. Hall

Theses and Dissertations

The use of continuous electric propulsion to manipulate a satellite’s orbit offers significant potential for enhancing coverage of a target in ways not previously considered. Elliptical orbits utilizing a very low perigee can facilitate access to the surface and atmosphere of the Earth at sub-ionosphere altitudes while counteracting atmospheric drag forces using continuous electric propulsion. Additionally, in-plane and out-of-plane manipulation of both circular and elliptical orbits can allow for passage of a satellite over a target at a given time. Sustained low perigee orbit was modeled with an initial perigee altitude of 100 km and various apogee altitudes to derive …

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Minimizing Losses In A Space Laser Power Beaming System, Charlie T. Bellows Mar 2010

Minimizing Losses In A Space Laser Power Beaming System, Charlie T. Bellows

Theses and Dissertations

A mathematical model is developed to track the amount of power delivered in a wireless laser power beaming system. In a wireless system the power proceeds through several different stages before being delivered to a payload for use. Each of these stages results in power losses that are thoroughly examined and modeled, allowing for the calculation of the likely amount of power delivered. Adjusting variable factors within the model allows for the optimization of the system for a specific task. The model shows that an optimized wireless power transfer system can deliver enough power to meet the space experiment objectives. …

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Global Navigation Satellite System Software Defined Radio, Jason M. Mcginthy Mar 2010

Global Navigation Satellite System Software Defined Radio, Jason M. Mcginthy

Theses and Dissertations

The GNSS world is quickly growing. The United States’ GPS, the European Union’s Galileo, China’s Compass, and Russia’s GLONASS systems are all developing or modernizing their signals, and there will soon be more navigation satellites in space than ever before. The goal of this research was to develop an initial capability for an AFIT GNSS software receiver. This software receiver is intended to be used for research purposes at the Advanced Navigation Technology (ANT) Center. First a GPS-only software receiver was built. It successfully acquired, tracked, and provided reasonable position estimates. Next, the receiver was successfully modified to acquire and …

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Verification Of Kam Theory On Earth Orbiting Satellites, Christian L. Bisher Mar 2010

Verification Of Kam Theory On Earth Orbiting Satellites, Christian L. Bisher

Theses and Dissertations

This paper uses KAM torus theory and Simplified General Perturbations 4 (SGP4) orbit prediction techniques compiled by Dr. William Wiesel and compares it to Analytical Graphics ® Incorporated (AGI) Satellite Toolkit ® (STK) orbit data. The goal of this paper is to verify KAM torus theory can be used to describe and propagate an Earth satellite orbit with similar accuracy to existing general perturbation techniques. Using SGP4 code including only truncated geopotential effects, KAM torus generating code, and other utilities were used to describe a particular satellite orbit as a torus and then propagate the satellite using traditional and KAM …

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Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston Mar 2010

Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston

Theses and Dissertations

This study was focused on obtaining accurate experimental data for the validation of the geometrically exact beam theory from a series of experiments in which high quality surface shape and deflection data was collected. Many previous experiments have experienced issues with data collection or test articles which the researchers were unable to overcome. The test program was performed in two stages: qualification and joined-wing. The qualification stage validated the experimental procedures on simple 72 in long aluminum beams with 8 in x 0.5 in cross-sections. The joined-wing stage was the primary experiment focused on obtaining quality data for use in …

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Disturbance Observer: Design And Flight Test Of A Large Envelope Flight Controller, Donevan A. Rein Mar 2010

Disturbance Observer: Design And Flight Test Of A Large Envelope Flight Controller, Donevan A. Rein

Theses and Dissertations

A new flight controller was evaluated through piloted simulation and flight test conducted at the USAF Test Pilot School. The controller, commonly called a disturbance observer, uses inertial sensor feedback routed through a simple control architecture that acts to force the desired response while rejecting sensor noise and atmospheric disturbances. The investigation included both handling qualities testing in the Octonian simulator at the Air Force Research Laboratories Air Vehicle Directorate, and initial flight test conducted as part of a Test Management Project at the USAF TPS. Simulation produced positive results with desired performance throughout a wide flight envelope. In addition, …

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Back-Pressure Effect On Shock-Train Location In A Scramjet Engine Isolator, Richard I. Paek Mar 2010

Back-Pressure Effect On Shock-Train Location In A Scramjet Engine Isolator, Richard I. Paek

Theses and Dissertations

The isolator of the scramjet decelerates the incoming high Mach flow to a lower Mach number and stabilizes the flow before it enters the combustor. Because of the unsteady combustion phenomenon and inconsistent completeness of the combustion, pressures within the combustor can vary drastically. These pressure variations can propagate forward and affect the flow field in the isolator - worst case unstarting the inlet. In this research, the shock train location versus the back-pressure is examined experimentally. The back-pressure is artificially created by symmetric (top & bottom) ramps that can close the flow area. Raising/lowering ramps result in higher/lower back-pressure. …

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Thrust And Performance Study Of Micro Pulsed Plasma, Jeremy J. Selstrom Mar 2010

Thrust And Performance Study Of Micro Pulsed Plasma, Jeremy J. Selstrom

Theses and Dissertations

This research is focused on several areas of the μPPT performance. An important idea studied is the effect of lifetime use on the performance. The thruster is fired for a simulated lifetime of use to see if there is an impact on the thrust of the thruster later in life. Also vital is the efficiency of the thruster. A μPPT performing at max efficiency will ionize all ablated material; however, we know that not to be the case. In this research the effort is made to collect these non-ionized particles in order to measure their mass post-test. With this collected …

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Structural Response Of Slotted Waveguide Antenna Stiffened Structure Components Under Compression, Joseph W. Sabat Jr. Mar 2010

Structural Response Of Slotted Waveguide Antenna Stiffened Structure Components Under Compression, Joseph W. Sabat Jr.

Theses and Dissertations

The Slotted Waveguide Antenna Stiffened Structure (SWASS) is an aircraft system that can provide the capabilities of a stiffened panel skin structure and a slotted waveguide radar antenna simultaneously. The system made from carbon fiber reinforced polymers is designed around a 10 GHz radar frequency in the X-band range and uses a WR-90 waveguide as a baseline for design. The system is designed for integration into fuselage or wing sections of intelligence, surveillance, and reconnaissance (ISR) aircraft and would increase the system performance through the availability of increased area and decreased system weight. Elemental parts of the SWASS structure were …

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Design Of A Film Cooling Experiment For Rocket Engines, Andrew L. Sincock Mar 2010

Design Of A Film Cooling Experiment For Rocket Engines, Andrew L. Sincock

Theses and Dissertations

The Film Cooling Rig (FCR) is a new test rig at the Air Force Institute of Technology (AFIT) to study film cooling for rocket engine applications. The original researcher designed, built, and then utilized the FCR to study radial curvature effects on film cooling for a non-combustion environment. This effort modified the FCR by adding propane-air combustion. Modular stainless steel test sections were produced to allow study of various curvatures and coolant injection angles. A pre-mixed burner was designed and built to deliver main flow mass flow rates necessary to produce blowing ratios as low as 0.5. A water cooling …

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Performance Of A Small Internal Combustion Engine Using N-Heptane And Iso-Octane, Cary W. Wilson Mar 2010

Performance Of A Small Internal Combustion Engine Using N-Heptane And Iso-Octane, Cary W. Wilson

Theses and Dissertations

With the sustained interest in Unmanned Aircraft Systems (UAS) and Micro Air Vehicles (MAV), the military services have a real need for vehicles powered by an internal combustion (IC) engine that can run efficiently on heavy hydrocarbon fuels, especially JP-8 due to established logistics. This thesis concerns the results of running a two horsepower, 4-stroke, spark-ignition engine (FUJI BF34-EI) with both iso-Octane and n-Heptane. Results include the knocking characteristic of this engine with n-Heptane, a comparison of the brake specific fuel consumption (BSFC) of the two fuels in a factory delivered engine configuration with a 17x10 APC propeller loading, a …

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Investigation Of A Novel Compact Vibration Isolation System For Space Applications, Steven D. Miller Mar 2010

Investigation Of A Novel Compact Vibration Isolation System For Space Applications, Steven D. Miller

Theses and Dissertations

A novel compact vibration isolation system was designed, built, and tested for the Space Chromotomography Experiment (CTEx) being built by Air Force Institute of Technology (AFIT) researchers. CTEx is a multifunctional experimental imaging chromotomographic spectrometer designed for flight on the International Space Station (ISS) and is sensitive to jitter caused by vibrations both through the support structure as well as those produced on the optical platform by rotating optical components. CTEx demands a compact and lightweight means of vibration isolation and suppression from the ISS structure. Vibration tests conducted on an initial isolator design resulted in changes in the chosen …

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Accurate Dynamic Response Predictions Of Pnpsat I, Michael D. Trottier Mar 2010

Accurate Dynamic Response Predictions Of Pnpsat I, Michael D. Trottier

Theses and Dissertations

Researchers at the Air Force Institute of Technology (AFIT) and the Operationally Responsive Space (ORS) Office have conducted extensive vibration testing and structural modeling on the first ORS Plug-and-Play Satellite (PnPSAT I). The intent of this research effort is to evaluate the premise that current post-integration spacecraft environmental test requirements can be reduced or modified using accurately tuned finite element (FE) models. As part of this research, modal testing was conducted on the PnPSAT I structural panels at AFIT. The modal testing was part of a much larger series of experimental trials on various configurations of PnPSAT I at the …

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Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu Mar 2010

Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu

Theses and Dissertations

In modern warfare navigation services are very important. GPS is currently providing service for accurate navigation, except in some areas, especially urban areas, where GPS signals cannot always be tracked by users. In these cases some additional navigation support could be provided by other global navigation satellite systems. If GPS is combined with other navigation systems than the navigation gap will be minor. In this thesis, the effect of combining GPS with other satellite navigation systems, specifically GLONASS, Galileo and Compass, is evaluated in terms of availability and position dilution of precision (PDOP) values. First, satellite constellations are simulated in …

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Estimating Characteristics Of A Maneuvering Reentry Vehicle Observed By Multiple Sensors, Evan M. Brooks Mar 2010

Estimating Characteristics Of A Maneuvering Reentry Vehicle Observed By Multiple Sensors, Evan M. Brooks

Theses and Dissertations

Post flight analysis of ballistic missile reentry vehicles is an area of focus for the U.S. Government, especially for those involved in ballistic missile defense. Typically, this analysis incorporates either a model-driven least squares filter or a data-following Kalman filter. The research performed here developed a filter that attempts to integrate the strengths of both filters. A least squares filter operates on observation data collected during exoatmospheric free flight and a Kalman filter is used to analyze data collected lower in the atmosphere, where potential maneuvers could be performed. Additionally, the filter was written to incorporate data from multiple sensors. …

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Prototype Development And Dynamic Characterization Of Deployable Cubesat Booms, Grant M. Thomas Mar 2010

Prototype Development And Dynamic Characterization Of Deployable Cubesat Booms, Grant M. Thomas

Theses and Dissertations

The current barrier to CubeSat proliferation is their lack of utility depth. These small satellites are exceptionally well suited for specific space missions such as space weather observation and other scientific data gathering exploits; however, they are not suited for every mission. The 10cm-cube form factor that gives the CubeSat its unique advantage is also its greatest hindrance. A potential bridge over this gap is the successful integration of deployable booms onto the CubeSat structure. With this research, the Air Force Institute of Technology (AFIT) explored the parameters of deployable tapespring booms using the triangular retractable and collapsible (TRAC) cross- …

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Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett Mar 2010

Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett

Theses and Dissertations

This research sought to validate a proof of concept regarding shape memory alloy actuation of a flapping-wing blimp. Specimen wires were subjected to cyclic voltage at increasing frequencies to quantify expected strains. A laser vibrometer captured 2048 sample velocities during single contraction and elongation cycles, and the resulting samples were used to calculate displacements. Displacements were determined ten times for each specimen and frequency to compute averages. Subsequently, a circumventing frame was designed to encase a blimp envelope and provide support for a flapping motion actuation system. Contraction of shape memory wire translated force to the flapping mechanism via bellcranks, …

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Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal Mar 2010

Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal

Theses and Dissertations

Current government and industry standards in spacecraft testing result in an Assembly, Integration, and Test (AIT) timeline greater than six months. These standards will not support the vision of Operationally Responsive Space (ORS) to deploy a satellite within six days to fill an urgent need. Using the Air Force Research Laboratory’s Plug-and-Play Satellite (PnPSat), multiple Rapid AIT trials were conducted. By exercising the AIT process with various spacecraft configurations and personnel, methods for reducing or modifying traditional testing regimen were investigated.

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Monocular Vision Localization Using A Gimbaled Laser Range Sensor, Don J. Yates Mar 2010

Monocular Vision Localization Using A Gimbaled Laser Range Sensor, Don J. Yates

Theses and Dissertations

There have been great advances in recent years in the area of indoor navigation. Many of these new navigation systems rely on digital images to aid an inertial navigation estimates. The Air Force Institute of Technology (AFIT) has been conducting research in this area for a number of years. The image-aiding techniques are centered around tracking stationary features in order to improve inertial navigation estimates. Previous research has used stereo vision systems or terrain constraints with monocular systems to estimate feature locations. While these methods have shown good results, they do have drawbacks. First, as unmanned exploration vehicles become smaller …

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Consideration Of Wear Rates At High Velocities, Stephen P. Meador Mar 2010

Consideration Of Wear Rates At High Velocities, Stephen P. Meador

Theses and Dissertations

The goal of this research is to study sliding contact wear of test sled slippers at high velocities. Experimentation representative of the slippers is infeasible, so numerical studies are used. An Eulerian-Lagrangian hydrocode called CTH is used to study mechanical wear. Failure criteria have been established to evaluate the stresses and strains resulting from the hydrocode simulation of a single asperity collision. The results from the hydrocode simulations are scaled to account for slipper bounce and multiple asperities, and these results produce total wear values that are approximately 90% of total experimental wear. Slipper thermodynamics have also been evaluated. The …

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Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love Mar 2010

Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love

Theses and Dissertations

Particle image velocimetry (PIV) has been carried out using solid carbon dioxide (CO2) particles as the seed material to continue the development of clean seeding for use in large-scale, closed-circuit tunnels. Testing occurred in two wind tunnels at subsonic and supersonic speeds using dry ice particles generated by allowing liquefied CO2 to expand from a small diameter injector tube through a larger diameter shroud tube. The particles were injected into the plenum and discrete solid particles, suitable for PIV measurements, were present in the test section. Data on particle size were first collected using a Malvern particle …

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