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Articles 3181 - 3210 of 5700
Full-Text Articles in Engineering
An Efficient Metaheuristic For Dynamic Network Design And Message Routing, Robert B. Hartlage
An Efficient Metaheuristic For Dynamic Network Design And Message Routing, Robert B. Hartlage
Theses and Dissertations
The implementation of Net-centric warfare presents major challenges in terms of effectively and efficiently delivering critical information across the Global Information Grid. In many cases, the amount of information requested will exceed the capabilities of the network. One challenge is to dynamically design the network (assign transceivers) to maximize the amount of required information that can be transmitted and the quality of service for those transmissions - to best implement the communications tasking order. The problem is as follows: given a list of required message traffic, to include source, destination, size, and priority, design the network to maximize the delivery …
Updating Optimal Decisions Using Game Theory And Exploring Risk Behavior Through Response Surface Methodology, Jeremy D. Jordan
Updating Optimal Decisions Using Game Theory And Exploring Risk Behavior Through Response Surface Methodology, Jeremy D. Jordan
Theses and Dissertations
This thesis utilizes game theory within a framework for updating optimal decisions based on new information as it becomes available. Methodology is developed that allows a decision maker to change his perceived optimal policy based on available knowledge of the opponents strategy, where the opponent is a rational decision maker or a random component nature. Utility theory is applied to account for the different risk preferences of the decision makers. Furthermore, response surface methodology is used to explore good risk strategies for the decision maker to approach each situation with. The techniques are applied to a combat scenario, a football …
Using Relocatable Bitstreams For Fault Tolerance, David P. Montminy
Using Relocatable Bitstreams For Fault Tolerance, David P. Montminy
Theses and Dissertations
This research develops a method for relocating reconfigurable modules on the Virtex-II (Pro) family of Field Programmable Gate Arrays (FPGAs). A bitstream translation program is developed which correctly changes the location of a partial bitstream that implements a module on the FPGA. To take advantage of relocatable modules, three fault-tolerance circuit designs are developed and tested. This circuit can operate through a fault by efficiently removing the faulty module and replacing it with a relocated module without faults. The FPGA can recover from faults at a known location, without the need for external intervention using an embedded fault recovery system. …
On-Demand Key Distribution For Mobile Ad-Hoc Networks, Daniel F. Graham
On-Demand Key Distribution For Mobile Ad-Hoc Networks, Daniel F. Graham
Theses and Dissertations
Mobile ad-hoc networks offer dynamic portable communication with little or no infrastructure. While this has many benefits, there are additional shortcomings specific to wireless communication that must be addressed. This research proposes gossip-based on-demand key distribution as a means to provide data encryption for mobile ad-hoc networks. This technique uses message keys to avoid encrypting and decrypting a message at every node. Other optimizations used include secure channel caching and joint rekey messages. The use of gossip makes the scheme robust to node failure. Experimental results show only a 15% increase in end-to-end delay with a node failure rate of …
Overcoming Tcp Degradation In The Presence Of Multiple Intermittent Link Failures Utilizing Intermediate Buffering, Duane F. Harmon
Overcoming Tcp Degradation In The Presence Of Multiple Intermittent Link Failures Utilizing Intermediate Buffering, Duane F. Harmon
Theses and Dissertations
It is well documented that assumptions made in the popular Transmission Control Protocol's (TCP) development, while essential in the highly reliable wired environment, are incompatible with today's wireless network realities in what we refer to as a challenged environment. Challenged environments severely degrade the capability of TCP to establish and maintain a communication connection with reasonable throughput. This thesis proposes and implements an intermediate buffering scheme, implemented at the transport layer, which serves as a TCP helper protocol for use in network routing equipment to overcome short and bursty, but regular, link failures. Moreover, the implementation requires no modifications to …
Hardware Realization Of A Transform Domain Communication System, Marshall E. Haker
Hardware Realization Of A Transform Domain Communication System, Marshall E. Haker
Theses and Dissertations
The purpose of this research was to implement a Transform Domain Communication System (TDCS) in hardware and compare experimental bit error performance with results published in literature. The intent is to demonstrate the effectiveness or ineffectiveness of a TDCS in communicating binary data across a real channel. In this case, an acoustic channel that is laden with narrowband interference was considered. A TDCS user pair was constructed to validate the proposed design using Matlab™ to control a PC sound card. The proposed TDCS design used the Bartlett method of spectrum estimation, the spectral notching algorithm found in TDCS literature, quadrature …
Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr
Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr
Theses and Dissertations
The constitutive relations traditionally used for finding shear stress and heat flux in a fluid become invalid in non-equilibrium flow. Their derivation from kinetic theory only demonstrates they are valid only for small deviations from equilibrium. Because it is fundamentally linked to non-equilibrium, entropy generation is used to investigate the limits of the continuum constitutive relations. However, the continuum equations are inherently limited to near equilibrium conditions due to the constitutive relations; thus kinetic theory must be used as a basis for comparison. Direct Simulation Monte Carlo (DSMC), a particle method alternative to continuum methods, is based on kinetic theory …
Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder
Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder
Theses and Dissertations
This research was done as part of an effort to develop alternative fire suppressant technologies for aircraft engine nacelles. A circular cylinder array was designed, built, and placed in the AFIT roll-around low speed wind tunnel to model generic clutter inside an engine nacelle. A turbulence grid was fabricated to enable measurements of the effects of turbulence level, independent of airspeed, on the flow over different model configurations. The wind tunnel test section was 12 inches wide x 12 inches high x 24 inches long. Pressure differential measurements were taken on various cylinder configurations. The configurations included one cylinder as …
Simulation Of The Dynamically Coupled Kc-135 Tanker And Refueling Boom, Jeremy J. Smith
Simulation Of The Dynamically Coupled Kc-135 Tanker And Refueling Boom, Jeremy J. Smith
Theses and Dissertations
Future Air Force requirements for the use of unmanned aircraft will require Automated Aerial Refueling (AAR). Current AAR research requires a precision model to simulate the refueling process of a KC-135 tanker and a UAV. There are existing high fidelity models of the tanker aircraft, refueling boom and proposed receiver aircraft. However, none of the models are coupled. Since boom orientation and motion is known to change the trim of the tanker aircraft, which in turn influences all other aspects of the refueling process, a new model is needed. The new model was created by integrating an existing KC-135 tanker …
The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker
The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker
Theses and Dissertations
Fuel efficiency of aircraft is of great importance to the military and private sector. A more efficient wing design for UAVs would lead to improvements in mission support while reducing fuel costs for the Air Force. An experimental investigation of one candidate design, the Houck Aircraft Configuration, has been conducted in the AFIT low speed wind tunnel. This aircraft shares similarities to other joined-wing aircraft, but includes curved flow-guides of varying spanwise camber connecting the upper and lower wingtips. Experimental results that the addition of flow guides on the 24" Houck Configuration results in a 2.5% reduction in L/D(sub max) …
Characterization Of A Hall Effect Thruster Using Thermal Imaging, James W. Tomaszewski
Characterization Of A Hall Effect Thruster Using Thermal Imaging, James W. Tomaszewski
Theses and Dissertations
A Hall thruster uses ionized xenon as a propellant for space propulsion applications. The heat produced by thruster components and the xenon plasma transfers to space and the spacecraft, impacting thruster and spacecraft design, as well as thruster efficiency and lifetime. Therefore, thermal information was gathered and analyzed in order to better understand the thermal characteristics of an operating thruster and to provide data applicable to improving the thruster efficiency and lifetime. This paper contains analysis of thruster temperatures obtained using a commercially available FLIR A40M thermographic imager in order to characterize a Busek Inc. 200W Hall Effect Thruster operating …
Investigating Hastily-Formed Collaborative Networks, Joshua S. Campbell, Stanley L. Cooley, Matthew F. Durkin, Brian K. Maddocks
Investigating Hastily-Formed Collaborative Networks, Joshua S. Campbell, Stanley L. Cooley, Matthew F. Durkin, Brian K. Maddocks
Theses and Dissertations
This research explores both the human and technical aspects of the network centric environment in the context of a major disaster or incident of national significance. The National Incident Management System (NIMS) is viewed by the authors as a social network, and an organizational topology is developed to improve its effectiveness. A rapid Network Deployment Kit (RNDK) using commercial off the shelf (COTS) wireless networking technology is also proposed that facilitates immediate NIMS implementation. The integration of logical and technical analyses forms a comprehensive systems engineering proposal to facilitate collaboration in a net-centric environment. It is envisioned that the methodology …
A Value-Focused Thinking Model For The Selection Of The Best Rigid Pavement, Partial-Depth Spall Repair Material, Benjamin G. Speer
A Value-Focused Thinking Model For The Selection Of The Best Rigid Pavement, Partial-Depth Spall Repair Material, Benjamin G. Speer
Theses and Dissertations
Concrete spalls on airfield pavements generate foreign object debris (FOD) that is damaging to aircraft engines, and may damage landing gear by roughening of the pavement surface. Repairing spalled concrete on aging and deteriorating airfields is essential for its safe operational use. Picking the best repair material from many products on the commercial market is difficult. There is wide variation on material properties, and good performance on certain criteria is critical to constructing long lasting repairs. Since there is currently no procedure for Air Force decision-makers to select the best rigid-pavement repair material, a model was created using Value-Focused Thinking …
Analyzing The Interdiction Of Sea-Borne Threats Using Simulation Optimization, Kristen L. Cavallaro
Analyzing The Interdiction Of Sea-Borne Threats Using Simulation Optimization, Kristen L. Cavallaro
Theses and Dissertations
Worldwide, maritime trade accounts for approximately 80% of all trade by volume and is expected to double in the next twenty years. Prior to September 11, 2001, Ports, Waterways and Coastal Security (PWCS) was afforded only 1 percent of United States Coast Guard (USCG) resources. Today, it accounts for nearly 22 percent of dedicated USCG resources. Tactical assessment of resource requirements and operational limitations on the PWCS mission is necessary for more effective management of USCG assets to meet the broader range of competing missions. This research effort involves the development and validation of a discrete-event simulation model of the …
Performance Evaluation Of Ad Hoc Routing In A Swarm Of Autonomous Aerial Vehicles, Matthew T. Hyland
Performance Evaluation Of Ad Hoc Routing In A Swarm Of Autonomous Aerial Vehicles, Matthew T. Hyland
Theses and Dissertations
This thesis investigates the performance of three mobile ad hoc routing protocols in the context of a swarm of autonomous unmanned aerial vehicles (UAVs). It is proposed that a wireless network of nodes having an average of 5.1774 log n neighbors, where n is the total number of nodes in the network, has a high probability of having no partitions. By decreasing transmission range while ensuring network connectivity, and implementing multi-hop routing between nodes, spatial multiplexing is exploited whereby multiple pairs of nodes simultaneously transmit on the same channel. The proposal is evaluated using the Greedy Perimeter Stateless Routing (GPSR), …
Analysis Of Routing Worm Infection Rates On An Ipv4 Network, James Gorsuch
Analysis Of Routing Worm Infection Rates On An Ipv4 Network, James Gorsuch
Theses and Dissertations
Malicious logic, specifically worms, has caused monetary expenditure problems to network users in the past. Worms, like Slammer and Code Red, have infected thousands of systems and brought the Internet to a standstill. This research examines the ability of the original Slammer worm, the Slammer based routing worm proposed by Zou et al, and a new Single Slash Eight (SSE) routing worm proposed by this research to infect vulnerable systems within a given address space. This research investigates the Slammer worm's ability to generate a uniform random IP addresses in a given address space. Finally, a comparison of the speed …
Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias
Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias
Theses and Dissertations
For urban combat reconnaissance, the flapping wing micro air vehicle concept is ideal because of its low speed and miniature size, which are both conducive to indoor operations. The focus of this research is the development of experimental methods best suited for the vibration testing of the wing structure of a flapping wing micro air vehicle. This study utilizes the similarity of a beam resonating at its first bending mode to actual wing flapping motion. While computational finite element analysis based on linear vibration theory is employed for preliminary beam sizing, an emphasis is placed on experimental measurement of the …
Sampled-Data Kalman Filtering And Multiple Model Adaptive Estimation For Infinite-Dimensional Continuous-Time Systems, Scott A. Sallberg
Sampled-Data Kalman Filtering And Multiple Model Adaptive Estimation For Infinite-Dimensional Continuous-Time Systems, Scott A. Sallberg
Theses and Dissertations
Kalman filtering and multiple model adaptive estimation (MMAE) methods have been applied by researchers in several engineering disciplines to a multitude of problems featuring a linear (or mildly nonlinear) model based on finite-dimensional differential (or difference) equations perturbed by random inputs. However, many real-world systems are more naturally modeled using an infinite-dimensional continuous-time linear systems model, such as those most naturally modeled as partial differential equations or time-delayed differential equations along with a possibly infinite-dimensional measurement model. The Kalman filtering technique was extended to encompass infinite-dimensional continuous-time systems with sampled-data measurements and a technique to approximate an infinite-dimensional continuous-time system …
Dynamic Response Of A Collidant Impacting A Low Pressure Airbag, Peter A. Dreher
Dynamic Response Of A Collidant Impacting A Low Pressure Airbag, Peter A. Dreher
Theses and Dissertations
There are many uses of low pressure airbags, both military and commercial. Many of these applications have been hampered by inadequate and inaccurate modeling tools. This dissertation contains the derivation of a four degree-of-freedom system of differential equations from physical laws of mass and energy conservation, force equilibrium, and the Ideal Gas Law. Kinematic equations were derived to model a cylindrical airbag as a single control volume impacted by a parallelepiped collidant. An efficient numerical procedure was devised to solve the simplified system of equations in a manner amenable to discovering design trends. The largest public airbag experiment, both in …
Diffusion Of Innovation: Factors Promoting Interest In Solar Photovoltaic Generation Systems Within Air Force Installations, Daniel Diaz Jr.
Diffusion Of Innovation: Factors Promoting Interest In Solar Photovoltaic Generation Systems Within Air Force Installations, Daniel Diaz Jr.
Theses and Dissertations
The purpose of this research was to identify factors which promote interest in solar photovoltaic generation systems for facility use within the United States Air Force. The construct model was developed based on past literature on Diffusion of Innovation Theory. The model comprised of measures defined as motivation, knowledge, experience, and familiarity as well as contextual variables. These measures were then used to determine whether any significant association existed between the measures and the overall dependent variable, interest. A phone interview was conducted on Air Force energy managers located within the continental U.S. The methods of correlation and regression analysis …
Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver
Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver
Theses and Dissertations
In an effort to increase the range of missiles and guided bombs, the USAF is looking at options for new wing configurations. One such configuration being considered is oblique wings. An oblique wing is a wing that pivots about a point on the aircraft fuselage thereby having one side swept forward and the other swept aft. Additional interest is looking at a wing only configuration that also rotates with one wing tip forward of the other. Studies have shown that this configuration can provide less drag for a given lift at both supersonic cruise and subsonic loiter conditions. This experiment …
Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel
Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel
Theses and Dissertations
The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV) for use in a closed circuit supersonic wind tunnel. The Air Force Institute of Technology (AFIT) closed circuit pressure-vacuum supersonic wind tunnel was utilized, which achieves a nominal Mach number of Mach 2.9 in a 2.5 inch by 2.5 inch square test section. CO2 was dispensed into the flow as a liquid from a standard compressed gas liquid tank through two different injector styles at two injection …
Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker
Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker
Theses and Dissertations
The development and use of Micro Air Vehicles is becoming more and more important to the military. Size, weight, maneuverability, stealth, and fuel consumption are just some of the constraints on a future Micro Air Vehicle. Perfect blueprints for a small scale flying machine are both insects and humming birds. Medium sized hummingbirds are found to have wings-beats at a frequency of 18-28 Hz. There is a vast amount of complexity to just how these creatures can create lift; however, this study looks at different beams made of common materials with 1st natural bending frequencies in this range. This study …
Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter
Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter
Theses and Dissertations
This research characterizes, in the elastic range, a scarf joint with overply using digital image correlation photogrammetry and finite element modeling. Additionally, the effect of varying the overply's geometric profile is examined. Specimens are constructed from AS4/3501-6 prepreg with a [0±45/90]2S layup. A fixture is used to achieve a consistent scarfed hole in each panel. The patch and adhesive (FM 300) are co-cured to the panels using positive pressure, which minimizes repair porosity. Three variations in the overply geometry are used: circular, rooftop-end, and tooth-end. The full strain field in each uni-axially loaded specimen is captured using digital image …
Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin
Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin
Theses and Dissertations
Satellite formations, otherwise known in the space community as satellite clusters or distributed satellite systems, have been studied extensively over the last 10 to 15 years. For use in remote sensing applications, formations consisting of smaller, simpler satellites provide numerous advantages over individual satellites. The image resolution capabilities of small-satellite formations constitute a significant technological leap in the ability to synthesize critical information. This research utilizes the nonlinear satellite dynamics, including gravitational perturbations, to search for the optimal fuel cost for maintaining a circular formation. The system dynamics were developed in an earth-centered inertial coordinate frame using the methods of …
Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews
Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews
Theses and Dissertations
During flight, launch, and reentry, external surfaces on aerospace vehicles undergo extreme thermo-acoustic loads resulting in structural degradation. Structural health monitoring techniques are being devised to evaluate the health of these structures by locating and quantifying structural damage during and after flight. One such technique uses Lamb wave propagation to assess damage on the surface and through the thickness of thin materials. The objective of this study was to assess the sensitivity of piezo-generated Lamb wave propagation to isothermal and thermal gradient environments using both theoretical and experimental methods. Experimental isothermal tests were conducted over a temperature range of 0-225 …
The Effects Of Microstructure On Fretting Fatigue Behavior Of Nickel Alloy In-100, Erik C. Saladin
The Effects Of Microstructure On Fretting Fatigue Behavior Of Nickel Alloy In-100, Erik C. Saladin
Theses and Dissertations
This thesis studied the effect of microstructure on the fretting fatigue behavior of IN-100. First, fretting and plain fatigue S-N curves were determined over a large range of applied stress at an identical R-ratio and for fretting tests, done with a constant contact load. It was found that fretting fatigue reduces the cycles to failure compared to plain fatigue. The half contact width was found for the specimens, the crack initiation angle was found to be 40 deg and the crack initiation location was at the trailing edge of contact for the fretting specimens. Computational work included finding the stress …
Selecting Electricity Generation Sources In Remote Locations, Kelly E. Kwan
Selecting Electricity Generation Sources In Remote Locations, Kelly E. Kwan
Theses and Dissertations
The purpose of this research was to investigate the impact of using a decision analysis technique for the selection of an electrical generation system for remote locations. Specifically, this thesis sought to answer five research questions addressing the types of energy sources used in remote locations, the decision-making processes used to identify these sources, the types of constraints incorporated in such a process, other valued factors, and their level of importance in relation to each other. The research questions were answered through a comprehensive literature review and the 10-Step Value-Focused Thinking Process on a specific case study in the National …
Using Value-Focused Thinking To Evaluate The Use Of Innovative Stormwater Management Technologies On Air Force Installations, Jeffrey T. Falcone
Using Value-Focused Thinking To Evaluate The Use Of Innovative Stormwater Management Technologies On Air Force Installations, Jeffrey T. Falcone
Theses and Dissertations
Stormwater runoff occurs naturally after every storm event; however, traditional development practices have created many impervious surfaces, such as buildings, parking lots, and streets that increase runoff volume and flow rate. Conventional stormwater management practices focus on collecting runoff into centralized channels and conveying it as quickly as possible to local bodies of water. This type of conveyance system decreases the opportunity for stormwater to naturally infiltrate back into the ground. It also prevents contaminants from being naturally filtered out of stormwater flows. As a result, centralized conveyance systems can cause flooding, erosion, and terrestrial and aquatic habitat degradation. Innovative …
Recommendations For A Standardized Program Management Office (Pmo) Time Compliance Network Order (Tcno) Patching Process, Michael Czumak Iii
Recommendations For A Standardized Program Management Office (Pmo) Time Compliance Network Order (Tcno) Patching Process, Michael Czumak Iii
Theses and Dissertations
Network security is a paramount concern for organizations utilizing computer technology, and the Air Force is no exception. Network software vulnerability patching is a critical determinant of network security. The Air Force deploys these patches as Time Compliance Network Orders (TCNOs), which together with associated processes and enforced timelines ensure network compliance. While the majority of the network assets affected by this process are Air Force owned and operated, a large number are maintained by external entities known as Program Management Offices (PMOs). Although these externally controlled systems provide a service to the Air Force and reside on its network, …