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Articles 8611 - 8640 of 11510
Full-Text Articles in Engineering
Factors And Interactions That Affect Air Force C-17 Aircraft Mission Capable Rates, Scotty A. Pendley
Factors And Interactions That Affect Air Force C-17 Aircraft Mission Capable Rates, Scotty A. Pendley
Theses and Dissertations
Given the high demand for mission capable airlift aircraft and considering increasing budget pressures, Air Mobility Command decision makers need a better understanding of mission capable (MC) rate-related factors and their interactions for mobility aircraft. This is needed to comprehend how issues such as airlift funding, current and future force reductions, and manning and experience levels may impact future MC rates for air mobility assets. Existing tools do not incorporate several key variables that the literature suggests are related to MC rates. Using a longitudinal approach, this thesis combines C-17 aircraft data with a structural equations modeling approach to evaluate …
Navigation Using Signals Of Opportunity In The Am Transmission Band, Jonathan A. Mcellroy
Navigation Using Signals Of Opportunity In The Am Transmission Band, Jonathan A. Mcellroy
Theses and Dissertations
Maintaining a precision navigation solution both in a GPS hostile jamming environment and also in a GPS non-compatible terrain area is of great importance. To that end, this thesis evaluates the ability to navigate using signals from the AM band of the electromagnetic spectrum (520 to 1710 kHz). Navigation position estimates are done using multi-lateration techniques similar to GPS. However, pseudoranges are created using Time Difference of Arrival (TDOA) distances between a reference receiver and a mobile receiver, allowing the mobile receiver to obtain absolute position estimates over time. Four methods were developed for estimating the cross-correlation peak within a …
Dual Fine Tracking Control Of A Satellite Laser Communication Uplink, Louis A. Noble
Dual Fine Tracking Control Of A Satellite Laser Communication Uplink, Louis A. Noble
Theses and Dissertations
A dual fine tracking control system (FTCS) is developed for a single aperture optical communication receiver to compensate for high frequency disturbances affecting tracking of two incident laser communication beams. The optical communication receiver resides within a payload module aboard a geosynchronous satellite, while each laser communication transmitter is housed within a module aboard a high altitude unmanned aerial vehicle (UAV). In addition to platform specific disturbances, the impact of atmospheric optical disturbances affecting tracking error are investigated. The system dynamics and FTCS are modeled and evaluated in MATLAB and SIMULINK. An optimal controller is developed to mitigate these disturbances …
Development And Testing Of A High-Speed Real-Time Kinematic Precise Dgps Positioning System Between Two Aircraft, Christopher J. Spinelli
Development And Testing Of A High-Speed Real-Time Kinematic Precise Dgps Positioning System Between Two Aircraft, Christopher J. Spinelli
Theses and Dissertations
This research involves the design, implementation, and testing of a high-speed, real-time kinematic, precise differential GPS positioning system for use in airborne applications such as automated aerial-refueling and close formation flying. Although many of the current ambiguity resolution techniques use the residuals from the least squares position estimation to determine the true ambiguity set, this thesis presents a novel approach to the ambiguity resolution problem, called the minimum indicator. Instead of assuming the ambiguity set with the lowest residuals is the true set, other special characteristics of the residuals are examined. This increases the confidence that the algorithm has selected …
Fast Scene Based Nonuniformity Correction With Minimal Temporal Latency, Christopher A. Rice
Fast Scene Based Nonuniformity Correction With Minimal Temporal Latency, Christopher A. Rice
Theses and Dissertations
The focus of this research was to derive a new algorithm for correction of gain nonuniformities in LIDAR focal plane arrays using as few frames as possible. Because of the current low production rate of LIDAR focal plane arrays there is a natural tendency for extreme nonuniformities to exist on a pixel by pixel basis as the manufacturing technique has not yet been perfected. Generally, nonuniformity correction techniques require a large number of frames and/or have obscure requirements on the translational shifts in the input image frames. This thesis presents a solution for finding multiplicative nonuniformities that exist in a …
Laser Covariance Vibrometry For Unsymmetrical Mode Detection, Michael C. Kobold
Laser Covariance Vibrometry For Unsymmetrical Mode Detection, Michael C. Kobold
Theses and Dissertations
Simulated cross - spectral covariance (CSC) from optical return from simulated surface vibration indicates CW phase modulation may be an appropriate phenomenology for adequate classification of vehicles by structural mode. The nonlinear structural to optical relationship is close to unity, avoiding nulls and high values; optical return contains sufficient spectral ID information necessary for data clustering. The FE model has contact between the homogeneous rolled armor and vehicle hull, a simple multi - layer skin model typical of most vehicles. Most of the high frequency energy moved to lower frequencies. This nonlinearity segments contact vibration modes into two classes: symmetrical …
Structural Analysis Of The Rigidizable Inflatable Get-Away-Special Experiment, Anna E. Gunn-Golkin
Structural Analysis Of The Rigidizable Inflatable Get-Away-Special Experiment, Anna E. Gunn-Golkin
Theses and Dissertations
The purpose of this research was to validate the structural integrity of the Rigidizable Inflatable Get-Away-Special Experiment (RIGEX) and make appropriate improvements to the design, motivated by static and dynamic analysis results. RIGEX is designed to advance the use of rigidizable inflatable structures in the space environment by providing three sets of on-orbit test data on the structural characteristics of three thermoplastic composite tubes. This thesis discusses the RIGEX structural analysis. The term structural analysis refers to the development of a detailed finite element model and the tests for which the model was used. The finite element model provided an …
Three Component Velocity Measurements In The Tip Vortex Of A Micro-Air-Vehicle, Hong-Joon Park
Three Component Velocity Measurements In The Tip Vortex Of A Micro-Air-Vehicle, Hong-Joon Park
Theses and Dissertations
The purpose of this research was to improve the MAV that will be used for battle damage assessment and reconnaissance or local surveillance through the experiments in AFIT wind tunnel. The experiments were performed to investigate the wing displacement and wing tip vortex interaction. To conduct the experiments, telescopic survey tool and tri-axial hot-wire anemometer was utilized. The results indicate that wing tip displacement of the flexible wing was approximately 8 times that of the rigid wing in an unstalled condition and data suggests that flexible wing has a denser core-distribution of velocity within the wing tip vortex and delays …
Optimal Dynamic Soaring For Full Size Sailplanes, Randel J. Gordon
Optimal Dynamic Soaring For Full Size Sailplanes, Randel J. Gordon
Theses and Dissertations
Dynamic soaring is a unique flying technique designed to allow air vehicles to extract energy from horizontal wind shears. Dynamic soaring has been used by seabirds like the Albatross to fly hundreds of kilometers a day across the ocean. Small hobby radio controlled sailplanes have also used this technique to achieve sustained speeds of over 200 miles per hour from just a simple hand toss. Dynamic soaring, however, has never before been studied for use on full size aircraft. The primary goal of this research was to prove or disprove the viability of dynamic soaring for enhancing a full size …
Some Aspects Of The Mechanical Response Of Pmr-15 Neat Resin At 288°C: Experiment And Modeling, Christina M. Falcone
Some Aspects Of The Mechanical Response Of Pmr-15 Neat Resin At 288°C: Experiment And Modeling, Christina M. Falcone
Theses and Dissertations
The mechanical response of PMR-15 neat resin was investigated at 288?C. Monotonic loading/unloading tests performed at several constant stress rates revealed considerable rate dependence, especially on the unloading path. Effect of prior stress rate on creep behavior was evaluated in creep tests preceded by uninterrupted loading to a target stress. Creep response was dependent on the prior stress rate. Effect of loading history was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. Comparison of creep strains accumulated during …
An Investigation Of The Effects Of Boundary Avoidance On Pilot Tracking, Randy D. Warren
An Investigation Of The Effects Of Boundary Avoidance On Pilot Tracking, Randy D. Warren
Theses and Dissertations
Pilot-Involved Oscillations (PIOs) remain a significant issue in the design, testing and operations of aerospace vehicles. Traditional methods for predicting, describing, and analyzing these events have provided the community with improved methods for minimizing the occurrences of PIOs. However, these events continue to occur over a wide range of aerospace vehicle types and over a wide range of pilot acumen. The introduction of boundary avoidance tracking (BAT) by Mr. William Gray in 2004 added a missing piece to the PIO puzzle. This theory presented that PIOs may result from increasing pilot gain resulting not from maintaining a specified condition, but …
Effects Of Polishing Shot-Peened Surfaces On Fretting Fatigue Behavior Of Ti-6al-4v, Kasey S. Scheel
Effects Of Polishing Shot-Peened Surfaces On Fretting Fatigue Behavior Of Ti-6al-4v, Kasey S. Scheel
Theses and Dissertations
The research of this thesis was done to investigate the effects of polishing a shot-peened specimen of Ti-6Al-4V on the fretting fatigue life of that specimen. The shot-peening process, though one of the most beneficial techniques in prolonging fretting fatigue life, creates a textured surface that may lead to problems on the micro level. This research was done in an attempt to further improve the peening process by examining the effects of another surface treatment to be used in conjunction, surface polishing. The rough peened surface may contain abrupt changes in surface geometry that act as stress risers, which are …
Experimental And Modeling Investigations Of Biomass Particle Combustion, Hong Lu
Experimental And Modeling Investigations Of Biomass Particle Combustion, Hong Lu
Theses and Dissertations
This investigation provides a comprehensive analysis of entrained-flow biomass combustion processes. Experimental and theoretical investigations indicate how particle shape and size influence biomass combustion rates. Experimental samples include flake-like, cylinder-like, and equant (nearly spherical) shapes with similar particle masses and volumes but different surface areas. Samples of small (less than 500 µm) particles were passed through a laboratory entrained-flow reactor in a nitrogen/air atmosphere and a maximum reactor wall temperature of 1600 K, while large samples were reacted in suspension in a single particle furnace operated at similar conditions as the entrained-flow reactor. A separately developed computer and image analysis …
Recovering Grain Boundary Inclination Parameters Through Oblique Double-Sectioning, Eric Richards Homer
Recovering Grain Boundary Inclination Parameters Through Oblique Double-Sectioning, Eric Richards Homer
Theses and Dissertations
A method for the retrieval of grain boundary inclination parameters of the grain boundary character distribution by oblique double-sectioning is proposed. The method, which is similar to the recovery of the orientation distributions from sets of incomplete pole-figures, is described along with a framework for implementation. The method directly measures grain boundary inclinations in a manner similar to serial sectioning while statistically sampling the microstructure comparably to stereological methods. Computer simulations of the method were used to confirm the mathematical framework. Additional simulations, where the grain boundary normal distributions were recovered by both oblique double-sectioning and stereological methods, showed that …
Analysis Of The Sediment Transport Capabilities Of Feswms Fst2dh, Mark K. Ipson
Analysis Of The Sediment Transport Capabilities Of Feswms Fst2dh, Mark K. Ipson
Theses and Dissertations
Many numeric models simulate the transport of sediment within rivers and streams. Engineers use such models to monitor the overall condition of a river or stream and to analyze the impact that the aggradation and degradation of sediment has on the stability of bridge piers and other features within a stretch of a river or stream. A model developed by the Federal Highway Administration, FST2DH, was recently modified to include the simulation of sediment movement within a channel. The tools for modeling sediment movement with FST2DH remain unproven. This thesis examines the sediment capabilities of FST2DH. It evaluates the sediment …
Adaptive Control Of Micro Air Vehicles, Joshua Stephen Matthews
Adaptive Control Of Micro Air Vehicles, Joshua Stephen Matthews
Theses and Dissertations
Although PID controllers work well on Miniature Air Vehicles (MAVs), they require tuning for each MAV. Also, they quickly lose performance in the presence of actuator failures or changes in the MAV dynamics. Adaptive control algorithms that self tune to each MAV and compensate for changes in the MAV during flight are explored. However, because the autopilots on MAVs are small, many of the adaptive control algorithms like those that employ least squares estimation may take too much code space, memory, and/or computing power. In this thesis we develop several Lyapunov-based model reference adaptive control (MRAC) schemes that are both …
Improved State Estimation For Miniature Air Vehicles, Andrew Mark Eldredge
Improved State Estimation For Miniature Air Vehicles, Andrew Mark Eldredge
Theses and Dissertations
Research in Unmanned Air Vehicles (UAV's) continues to push the limitations of size and weight. As technical advances have made UAV's smaller and less expensive, they have become more flexible and extensive in their roles. To continue using smaller and less expensive components while retaining and even enhancing performance requires more sophisticated processing of sensor data in order for the UAV to accurately determine its state and thereby allow the use of feedback in controlling the aircraft automatically. This work presents a three-stage state-estimation scheme for the class of UAV's know as Miniature Air Vehicles (MAV's). The first stage estimates …
Modeling And Validation Of Tension-Element Based Mechanisms For Golf Ball-Club Impact, Aaron Robison
Modeling And Validation Of Tension-Element Based Mechanisms For Golf Ball-Club Impact, Aaron Robison
Theses and Dissertations
Previous work has systematically and numerically demonstrated feasibility and performance benefits of the tension-element concept in golf club heads; however, higher fidelity models needed to be created and validated for this concept. There is a need for more accurate models for this concept to further investigate its performance benefits. Performance is measured in terms of impact efficiency of the ball and head and is referred to as coefficient of restitution (COR). COR is affected by the dynamic effective face stiffness and mass properties of the club. This thesis creates and validates high-fidelity, non-linear, dynamic finite element models for the tension-element …
Video Stabilization And Target Localization Using Feature Tracking With Video From Small Uavs, David Linn Johansen
Video Stabilization And Target Localization Using Feature Tracking With Video From Small Uavs, David Linn Johansen
Theses and Dissertations
Unmanned Aerial Vehicles (UAVs) equipped with lightweight, inexpensive cameras have grown in popularity by enabling new uses of UAV technology. However, the video retrieved from small UAVs is often unwatchable due to high frequency jitter. Beginning with an investigation of previous stabilization work, this thesis discusses the challenges of stabilizing UAV based video. It then presents a software based computer vision framework and discusses its use to develop a real-time stabilization solution. A novel approach of estimating intended video motion is then presented. Next, the thesis proceeds to extend previous target localization work by allowing the operator to easily identify …
Determining The Value Of A Master's Degree In Construction Management, Benjamin K. Davis
Determining The Value Of A Master's Degree In Construction Management, Benjamin K. Davis
Theses and Dissertations
The purpose of this study is to determine the value of a master's degree in construction management in southern Idaho. A telephone and Internet survey was employed to determine the value that members of the construction industry in southern Idaho place on construction management (CM) degrees, both graduate and undergraduate. The survey included 27 self-described general contractors who are members of The Associated General Contractors of America (AGC) in regions 3 and 4 in the state of Idaho. Regions three and four include Twin Falls, Idaho Falls, Pocatello, Ketchum, Burley and surrounding communities. Following the compilation of surveys, it was …
Melt Detection And Estimation In Greenland Using Tandem Quikscat And Seawinds Scatterometers, Brandon R. Hicks
Melt Detection And Estimation In Greenland Using Tandem Quikscat And Seawinds Scatterometers, Brandon R. Hicks
Theses and Dissertations
Ku-band dual-polarization radar backscatter measurements from the SeaWinds on QuikScat (QuikScat) and SeaWinds on ADEOS-2 (SeaWinds) scatterometers are used to classify the melt state and estimate melt severity in Greenland. Backscatter measurements are organized into high temporal and high spatial resolution images created using the Scatterometer Image Reconstruction (SIR) algorithm and a new temporal data segmentation technique. Melt detection is performed using a layered electromagnetic model combined with a Markov chain model. The new melt detection method allows classification of the snow-pack into three states: melt, refreeze, and frozen. Melt severity and refreeze severity indexes are also developed. The melt …
Modeling The Mechanical Effects Of Liquid Mediated Adhesion Between The Human Vocal Folds, Gifford Zach Decker
Modeling The Mechanical Effects Of Liquid Mediated Adhesion Between The Human Vocal Folds, Gifford Zach Decker
Theses and Dissertations
The vocal folds are a complex self-oscillating biological system. In the current research, an equation was developed to model viscous adhesion forces that occur when the collision of the vocal folds results in the formation of a liquid bridge. The adhesion equation was validated using experimental data, and simplified to a one-dimensional approximation with an included correction factor that adjusted the predicted pressure in situations where the one-dimensional approximation was invalid. A non-oscillating vocal fold model with a modeled liquid bridge was used to study stress resulting from viscous adhesion. The vertical normal stress magnitude ranged from about 80 to …
Comparing Time And Accuracy Of Building Information Modeling To On-Screen Takeoff For A Quantity Takeoff Of A Conceptual Estimate, Morgan A. Alder
Comparing Time And Accuracy Of Building Information Modeling To On-Screen Takeoff For A Quantity Takeoff Of A Conceptual Estimate, Morgan A. Alder
Theses and Dissertations
Estimating is a critical aspect of every construction project. The most tedious component of an estimate is the quantity takeoff. Different tools are available to improve an estimator's productivity for a quantity takeoff. Faster quantity takeoffs enable estimator to bid more jobs. This study analyzed the time and accuracy of performing quantity takeoffs when using building information modeling (BIM) through a comparison study using Revit (BIM software) and On-Center's OST. In preparation for the study the researcher conducted a pilot study. Participants of the study were asked to perform a quantity takeoff using both Revit and OST. Their resulting data …
Contractor Variability In Construction Of Cement Treated Base Layers, Maile Anne Rogers
Contractor Variability In Construction Of Cement Treated Base Layers, Maile Anne Rogers
Theses and Dissertations
The primary purposes of this research were to identify construction factors most correlated to specific mechanical properties of cement-treated base (CTB) layers and to determine which construction factors exhibit comparatively high variability within individual construction sections of the two pavement reconstruction projects included in this study. In addition, differences between construction sections tested in this research were evaluated. The research focused on the construction of CTB layers in two pavement reconstruction projects in northern Utah, one along Interstate 84 (I-84) near Morgan and one along U.S. Highway 91 (US-91) near Richmond. The significant predictor variables associated with California bearing ratio …
Microwave Remote Sensing Of Saharan Ergs And Amazon Vegetation, Haroon Stephen
Microwave Remote Sensing Of Saharan Ergs And Amazon Vegetation, Haroon Stephen
Theses and Dissertations
This dissertation focuses on relating spaceborne microwave data to the geophysical characteristics of the Sahara desert and the Amazon vegetation. Radar and radiometric responses of the Saharan ergs are related to geophysical properties of sand formations and near surface winds. The spatial and temporal variability of the Amazon vegetation is studied using multi-frequency and multi-polarization data. The Sahara desert includes large expanses of sand dunes called ergs that are constantly reshaped by prevailing winds. Radar backscatter measurements observed at various incidence and azimuth angles from the NASA Scatterometer (NSCAT), the ERS scatterometer (ESCAT), the SeaWinds scatterometer aboard QuikScat (QSCAT), and …
Incorporating Wireless Power Transfer In An Led Lighting Application, Jonathan S. Shipley
Incorporating Wireless Power Transfer In An Led Lighting Application, Jonathan S. Shipley
Theses and Dissertations
There are various situations in which electrical energy is desired but cannot by conveniently supplied. Since the days of Hienrich Hertz and Nikola Tesla, scientists have tried to solve this problem using different methods of wireless power transfer. Today, wireless power transfer has only been commercially demonstrated at small distances through use of induction. This thesis demonstrated the transfer of wireless power at relatively large distances through radio frequencies in the development of a prototype for a commercial product - a wireless household lamp.
A Solution For Commodity Field Hauling With Self-Unloading Semi-Trailers, Lee Pagens Wilkerson
A Solution For Commodity Field Hauling With Self-Unloading Semi-Trailers, Lee Pagens Wilkerson
Theses and Dissertations
Commodity hauling of bulk goods is a growing enterprise that has expanded from hauling agricultural products to hauling many other bulk products. Commodity trailers are used to haul agricultural products from storage facilities to processing plants. These trailers are designed for highway use but are frequently required to work in field conditions as well. In many cases this environment overstresses these trailers and results in permanent irreparable damage. In addition to the structural problems of these trailers, the current systems for unloading the bulk produce from these trailers have serious inadequacies. While functional, the currently used chain and non-chain driven …
Development Of An Index For Concrete Bridge Deck Management In Utah, Ellen T. White
Development Of An Index For Concrete Bridge Deck Management In Utah, Ellen T. White
Theses and Dissertations
The purpose of this research was to develop a new index for concrete bridge deck management in Utah. Data were collected in the summer of 2005 from 15 concrete bridge decks in the vicinity of Salt Lake City. The decks ranged from 2 to 21 years in age and were all constructed using epoxy-coated rebar. Visual inspection, sounding, Schmidt hammer testing, half-cell potential testing, and chloride concentration testing were performed on six 6-ft by 6-ft test areas randomly distributed within the single lane closed to traffic on each deck, and testing protocols followed American Society for Testing and Materials standards …
Numerical Modeling Of Blast-Induced Liquefaction, Wayne Yeung Lee
Numerical Modeling Of Blast-Induced Liquefaction, Wayne Yeung Lee
Theses and Dissertations
A research study has been conducted to simulate liquefaction in saturated sandy soil induced by nearby controlled blasts. The purpose of the study is to help quantify soil characteristics under multiple and consecutive high-magnitude shock environments similar to those produced by large earthquakes. The simulation procedure involved the modeling of a three-dimensional half-space soil region with pre-defined, embedded, and strategically located explosive charges to be detonated at specific time intervals. LS-DYNA, a commercially available finite element hydrocode, was the solver used to simulate the event. A new geo-material model developed under the direction of the U.S. Federal Highway Administration was …
Design Of A Linear Ultrasonic Piezoelectric Motor, Scott L. Sharp
Design Of A Linear Ultrasonic Piezoelectric Motor, Scott L. Sharp
Theses and Dissertations
A new geometrically unique ultrasonic motor (USM) was designed using finite element modeling (FEM). A USM operates by vibrating a drive tip in an elliptical motion while it is in periodic contact with a driven surface. Piezoelectric elements are used to create the elliptical motions and are driven near a resonant frequency to create the needed displacements for the motor to operate. An idea for a motor frame was conceived that consisted of an arch, a center ground, and two piezoelectric elements connected to the center ground. End caps were added between the frame and the piezoelectric elements to reduce …