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Articles 2941 - 2970 of 5700
Full-Text Articles in Engineering
Improving Mixed Variable Optimization Of Computational And Model Parameters Using Multiple Surrogate Functions, David Bethea
Improving Mixed Variable Optimization Of Computational And Model Parameters Using Multiple Surrogate Functions, David Bethea
Theses and Dissertations
This research focuses on reducing computational time in parameter optimization by using multiple surrogates and subprocess CPU times without compromising the quality of the results. This is motivated by applications that have objective functions with expensive computational times at high fidelity solutions. Applying, matching, and tuning optimization techniques at an algorithm level can reduce the time spent on unprofitable computations for parameter optimization. The objective is to recover known parameters of a flow property reference image by comparing to a template image that comes from a computational fluid dynamics simulation, followed by a numerical image registration and comparison process. Mixed …
Selecting The Best Thermal Building Insulation Using A Multi-Attribute Decision Model, Theodore J. Sotoropolis
Selecting The Best Thermal Building Insulation Using A Multi-Attribute Decision Model, Theodore J. Sotoropolis
Theses and Dissertations
Thermal building insulation has traditionally been viewed as a means to reduce thermal conductivity through the building envelope. Builders typically choose the least expensive material which meets the specifications in order to remain competitive. Other factors regarding long term health and environmental consequences are typically dismissed. However, a recent shift toward sustainability requires that architects and engineers take a more responsible approach to building design. This research takes a holistic approach to selecting thermal building insulation through the use of a multi-attribute decision model. Several types of insulating products from a variety of manufacturers were investigated in order to determine …
Micro-Etched Platforms For Thermal Inactivation Of Bacillus Anthracis And Bacillus Thuringiensis Spores, Leslie S. Hawkins
Micro-Etched Platforms For Thermal Inactivation Of Bacillus Anthracis And Bacillus Thuringiensis Spores, Leslie S. Hawkins
Theses and Dissertations
This research developed and applied microlithography techniques to etch microscope slide platforms in order to measure thermal inactivation of Bacillus thuringiensis and Bacillus anthracis spores, two closely related Bacillus species. B.t. is widely used as a surrogate for B.a. in response studies and in some field studies. This work addressed the previously identified problem of measuring both spore growth and spore thermal kill threshold using the traditional method of spreading a diluted spore solution on a plate. The micro-etched platforms forced spore separation thereby preventing neighbor growth from obscuring germination and initial vegetative growth measurements using a microscope. The technique …
Factors Leading To Effectiveness And Satisfaction In Civil Engineer Information Systems, Donald C. Crabtree
Factors Leading To Effectiveness And Satisfaction In Civil Engineer Information Systems, Donald C. Crabtree
Theses and Dissertations
The Air Force Civil Engineer Support Agency (AFCESA) has developed information systems in support of civil engineer operations. Over the last decade, the number of systems has grown to support the breadth of civil engineer functions. At this time, numerous (900+) decentralized systems support civil engineer functions around the world. Due to budget constraints, AFCESA is transforming civil engineer business processes to leverage the workforce in an optimized fashion. In support of this transition, AFCESA is posturing to acquire new information systems in support of civil engineer business processes. To help AFCESA improve upon its suite of information systems development …
An Analysis Of Construction Cost And Schedule Performance, Michael J. Beach
An Analysis Of Construction Cost And Schedule Performance, Michael J. Beach
Theses and Dissertations
Cost and schedule performance are widely accepted in the literature and in industry as effective measures of the success of the project management effort expended. Earned Value Analysis (EVA) offers many metrics to objectively measure cost and schedule performance of many different types of projects. The author utilized EVA to objectively measure the cost and schedule performance of completed United States Air Force (AF) Military Construction (MILCON projects from 1990 to 2005. The impact of Major Command (MAJCOM), Construction Agent (CA), and facility type (CATCODE) and the combination of these variables on the EVA metrics of Cost Performance Index (CPI), …
The Concept Design Of A Split Flow Liquid Hydrogen Turbopump, Michael A. Arguello
The Concept Design Of A Split Flow Liquid Hydrogen Turbopump, Michael A. Arguello
Theses and Dissertations
An initial design of a split flow liquid hydrogen turbopump for the Dual Expander Aerospike Nozzle (DEAN) upper stage engine was completed. The engine nozzle is an annular aerospike. The engine cycle requires a combustion chamber pressure of 1,740 psia. The DEAN is designed to deliver 57,200 lbf of thrust and 472 seconds of Isp. The turbopump design was completed using a meanline software tool. The design consists of a single piece rotor, with a two-stage pump and radial inflow turbine. The turbopump flow rates are 15.1 and 7.55 lbm/s into the first and second stage, respectively. The first and …
An Experimental Technique For Developing Intermediate Strain Rates In Ductile Metals, Hugh E. Gardenier Iv
An Experimental Technique For Developing Intermediate Strain Rates In Ductile Metals, Hugh E. Gardenier Iv
Theses and Dissertations
Quantifying the strain-rate sensitive dynamic properties of structural materials is an important area of research in the solid mechanics field. Property evaluation is typically accomplished using dynamic tests which involve rapid loading or impact of specimens. In these tests, inertial forces and wave propagation make it difficult to accurately record the material response to a loading condition at an equivalent location. Furthermore, these tests typically generate high strain rates (in excess of 103 s−1) and an experimental method for generating rates of strain in the intermediate strain rate regime which is relatively simple, low cost, and reliable …
Analysis Of Multi-Layered Materials Under High Velocity Impact Using Cth, Jason K. Lee
Analysis Of Multi-Layered Materials Under High Velocity Impact Using Cth, Jason K. Lee
Theses and Dissertations
Multi-layer armor containing ceramic and metallic layers has become more common in the past two decades. Typically, ceramics have high compressive strength which combined with their low density make them highly desirable for armor applications. This research effort numerically simulates high velocity impact of cylindrical projectiles on multi-layer metallic and ceramic targets of finite thickness. The impact of the projectile occurs normal to the surface of the target. The projectiles used are made of either S7 tool steel or tungsten. The targets consist of either rolled homogeneous armor, 4340 steel and boron carbide ceramic or rolled homogeneous armor and boron …
On-Board Thermal Management Of Waste Heat From A High-Energy Device, Nathan D. Klatt
On-Board Thermal Management Of Waste Heat From A High-Energy Device, Nathan D. Klatt
Theses and Dissertations
The use of on-board high-energy devices such as megawatt lasers and microwave emitters requires aircraft system integration of thermal devices to either rid waste heat or utilize it in other areas of the aircraft. Non-chemical lasers are among the most challenging applications due to the low cooling temperature requirements (67 °F) and high waste heat generation times of order 20 s. (Microwave devices will be cooled at 157.7 °F.) One plan calls for the rapidly generated waste energy to be stored prior to peripheral utilization, with subsequent removal of the heat over a 5-10 minute span. A method is presented …
Computational Design Of Upperstage Chamber, Aerospike, & Cooling Jacket For Dual-Expander Rocket Engine, David F. Martin Ii
Computational Design Of Upperstage Chamber, Aerospike, & Cooling Jacket For Dual-Expander Rocket Engine, David F. Martin Ii
Theses and Dissertations
To increase the performance of the current US satellite launch capability, new rocket designs must be undertaken. One concept that has been around since the 50s but yet to be utilized on a launch platform is the aerospike, or plug nozzle. The aerospike nozzle concept demonstrates globally better performance compared to a conventional bell nozzle, since the expansion of the jet is not bounded by a wall and therefore can adjust to the environment by changing the outer jet boundary. A dual-expander aerospike nozzle (DEAN) rocket concept would exceed the Integrated High Payoff Rocket Propulsion Technology initiative (IHPRPT) phase three …
Optimal Guidance Of A Relay Mav For Isr Support Beyond Line-Of-Sight, John H. Hansen
Optimal Guidance Of A Relay Mav For Isr Support Beyond Line-Of-Sight, John H. Hansen
Theses and Dissertations
This thesis developed guidance laws to optimally position a relay Micro-UAV (MAV) to provide an operator with real-time Intelligence, Surveillance, and Reconnaissance (ISR) by relaying communication and video signals when there is no line-of-sight between the operator at the base and the rover MAV performing the ISR mission. The ISR system consists of two MAVs, the Relay and the Rover, and a Base. The Relay strives to position itself to minimize the radio frequency (RF) power required for maintaining communications between the Rover and the Base, while the Rover performs the ISR mission, which may maximize the required RF power. …
Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather
Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather
Theses and Dissertations
We consider radiation counting experiments used to measure quantities of materials that are short-lived with respect to the count durations. The HPS 13.31 statistical analysis seriously overestimates the uncertainty when the quantity and background are very low. We consider the case in which the objective is to quantify the number of atoms, n, that were present in a sample when it was drawn. Mathews and Gerts [JRNC, 2008] analyzed this case and developed formulas for the probability distribution of n, in order to develop experiment design processes that minimize the smallest detectable quantity of material, thus maximizing sensitivity for the …
Finite Element Simulation Methods For Dry Sliding Wear, Aaron J. Chmiel
Finite Element Simulation Methods For Dry Sliding Wear, Aaron J. Chmiel
Theses and Dissertations
The Holloman High Speed Test Track is a rocket sled track for testing at hypersonic velocities. However, there are customers that desire to test at even greater velocities. In order to achieve higher velocities there are several phenomena that must be overcome. One important phenomenon is wear of the shoe that holds the sled on the rail. This research is a look at the feasibility of using finite element analysis to predict the wear of the shoe during a test run down the track. Two methods are investigated, one is a macro-scale, incremental method utilizing traditional wear equations from Archard, …
Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents
Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents
Theses and Dissertations
Filtered Rayleigh Scattering (FRS) is a non-intrusive, laser-based flow characterization technique that consists of a narrow linewidth laser, a molecular absorption filter, and a high resolution camera behind the filter to record images. Gases of different species have different molecular scattering cross-sections that become apparent as they pass through the interrogating laser light source, and this difference is used to discriminate between the different gaseous components. This study focuses on the behavior of a buoyant helium jet exiting horizontally into ambient air, and more specifically this jet’s tendency to form side lobes that are discharged from the core fluid under …
A Static Aeroelastic Analysis Of A Flexible Wing Mini Unmanned Aerial Vehicle, Nathan A. Pitcher
A Static Aeroelastic Analysis Of A Flexible Wing Mini Unmanned Aerial Vehicle, Nathan A. Pitcher
Theses and Dissertations
The static aeroelastic behavior of the Nighthawk mini unmanned aerial vehicle is examined using a combined experimental and computational approach. Three wings are examined. In order of increasing stiffness they are: a flexible wing, a stiff wing, and a fictitious rigid wing with zero deflection. Photogrammetry is used during wind tunnel testing to measure the average deflected shape of the flexible and stiff wings during flight. The independent variables during wind tunnel tests are angle of attack (ranging from −5.1° through 13.4°) and velocity, which is 20 mph, 30 mph, and 40 mph. Roll angle and yaw angle are control …
Biomimetic Micro Air Vehicle Testing Development And Small Scale Flapping-Wing Analysis, Craig E. Svanberg
Biomimetic Micro Air Vehicle Testing Development And Small Scale Flapping-Wing Analysis, Craig E. Svanberg
Theses and Dissertations
The purpose of this research was to develop testing methods capable of analyzing the performance of a miniature flapping-wing mechanism that can later be adapted to a biomimetic micro air vehicle (MAV). Three small scale flapping mechanisms capable of single plane flapping, flapping with active pitch control, and flapping/pitch with out-of-plane movement were designed using SolidWorks. The flapping-only model was fabricated on an Objet Eden 500V 3-dimensional printer. The flapping mechanism was mounted on an aluminum plate supported by air bearings, and thrust was measured for a variety of conditions. The testing was conducted using wings composed of carbon fiber …
Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright
Minimizing Secular J2 Perturbation Effects On Satellite Formations, Jonathan W. Wright
Theses and Dissertations
The purpose of this thesis is to examine the secular effects of the J2 oblateness perturbation on close proximity satellites. The main objective is to analyze the deputy’s position and velocity with respect to the chief and adjust the initial conditions of the deputy in an attempt to minimize the secular effects of J2 perturbations. Previous work has provided a method of obtaining a closed form solution for J2 invariance with co-planar orbits. Therefore, this work will primarily consider deputy orbits that experience motion outside of the chief’s orbital plane. Upon determining the required initial conditions, the …
Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis
Modeling Gps Satellite Orbits Using Kam Tori, Rachel M. Derbis
Theses and Dissertations
Global Positioning System (GPS) satellite orbits are modeled using Kolmogorov, Arnold, Moser (KAM) tori. Precise Global Positioning System satellite locations are analyzed using Fourier transforms to identify the three basis frequencies in an Earth Centered, Earth Fixed (ECEF) rotating reference frame. The three fundamental frequencies are 1) the anomalistic frequency, 2) a combination of earth’s rotational frequency and the nodal regression rate, and 3) the apsidial regression rate. A KAM tori model fit to the satellite data could be used to predict future satellite locations. This model would allow rapid determination with fewer computational requirements than the typical method of …
Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens
Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens
Theses and Dissertations
Demonstration of a strategy to perform two-dimensional diode laser tomography using a priori knowledge from symmetry arguments and computational fluid dynamic (CFD) calculations is presented for a flat flame burner. The strategy uses an optimization technique to determine flame diameter and location using a vector quantization approach. Next, the variance in a training set, produced from CFD calculations, is captured using principal components analysis. The information in the training set allows interpolation between beam paths resulting in temperature and density maps. Finally, the TDLAS temperature and density maps are shown to agree with traditional thermocouple measurements of the flat flame …
Analyzing Carbohydrate-Based Regenerative Fuel Cells As A Power Source For Unmanned Aerial Vehicles, Olek Wojnar
Analyzing Carbohydrate-Based Regenerative Fuel Cells As A Power Source For Unmanned Aerial Vehicles, Olek Wojnar
Theses and Dissertations
Based on current capabilities, we examine the feasibility of creating a carbohydrate-based regenerative fuel cell (CRFC) as the primary power source for unmanned aerial vehicles (UAV) for long endurance missions where station keeping is required. A CRFC power system is based on a closed-loop construct where carbohydrates are generated from zooxanthellae, algae that create excess carbohydrates during photosynthesis. The carbohydrates are then fed to a carbohydrate fuel cell where electric power is generated for the UAV’s propulsion, flight control, payload, and accessory systems. The waste products from the fuel cell are used by the zooxanthellae to create more carbohydrates, therefore …
C-5a Galaxy Systems Engineering Case Study, Air Force Center For Systems Engineering, John M. Griffin
C-5a Galaxy Systems Engineering Case Study, Air Force Center For Systems Engineering, John M. Griffin
AFIT Documents
The C-5 Systems Engineering Case Study captures the untold story of the application of systems engineering during the concept exploration, development, and production of the USAF C-5A and C-5B aircraft. The case study examines and dissects the systems engineering process as applied by the Air Force C-5 System Program Office and the prime contractor, Lockheed, Georgia, from the program s genesis in 1957 to the last delivery of the C-5A and the beginning of the C-5B program in 1973. Numerous interviews were conducted with the principals who managed and directed the program and a story of the systems engineering process …
Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert
Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert
Theses and Dissertations
The thermal characteristics of a Hall thruster directly influence thruster and spacecraft design. High temperatures affect the magnetic coil capabilities and cause higher insulator erosion rates, influencing both thruster performance and lifetime. The Hall thruster transfers heat through both radiation and conduction, and the spacecraft must handle this additional thermal energy. An infrared camera provides a non-intrusive method to analyze the thermal characteristics of an operational Hall thruster. This thesis contains the thermal analysis of a Busek Co. Inc. 200 W Hall thruster, using a FLIR ThermaCAM SC640 infrared camera. The Space Propulsion Analysis and System Simulator Laboratory at the …
Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya
Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya
Theses and Dissertations
This research effort develops a program using MATLAB® to solve the equations of motion for the atmospheric reentry of the Crew Exploration Vehicle (CEV) which is assumed to be in the phase of a lunar return trajectory that could be initiated any time during the mission. The essential reason for this research is to find a solution for the problem of an unplanned lunar return in addition to the normal procedures. Unlike Apollo type missions, the CEV would still be able to land on any preplanned available landing sites without any additional delay. In Apollo type missions, the return phase …
Hubble Space Telescope Systems Engineering Case Study, Air Force Center For Systems Engineering, James J. Mattice
Hubble Space Telescope Systems Engineering Case Study, Air Force Center For Systems Engineering, James J. Mattice
AFIT Documents
The Hubble Space Telescope (HST) is an orbiting astronomical observatory operating in the spectrum from the near-infrared into the ultraviolet. Launched in 1990 and scheduled to operate through 2010, HST carries and has carried a wide variety of instruments producing imaging, spectrographic, astrometric, and photometric data through both pointed and parallel observing programs. Over 100,000 observations of more than 20,000 targets have been produced for retrieval. A macroscopic, cumulative representation of these observations is shown in the figure below to provide a sense of the enormous volume of astronomical data collected by the HST about our universe, our beginnings, and, …
Determination Of Static And Dynamic Stability Derivatives Using Beggar, Michael E. Bartowitz
Determination Of Static And Dynamic Stability Derivatives Using Beggar, Michael E. Bartowitz
Theses and Dissertations
The static and dynamic pitch and roll stability derivatives of a finned, axisymmetric missile known as the Basic Finner were examined using a Computational Fluid Dynamics (CFD) approach. Stability derivatives are used to characterize vehicle motion, and knowledge of them is critical to the design of stable uncontrolled vehicles and control systems for controlled vehicles. Using CFD to characterize the motion of new munition designs has the potential to improve overall performance and reduce research and testing costs. The present analysis simulated forced oscillation and free oscillation of the Basic Finner model using the Air Force SEEK EAGLE Office's Beggar …
A Comparison Of Moiré Interferometry And Digital Image Correlation, Ryan J. Davidson
A Comparison Of Moiré Interferometry And Digital Image Correlation, Ryan J. Davidson
Theses and Dissertations
This research effort studied the effect of subset size and step size on the spatial resolution and accuracy of Digital Image Correlation (DIC). In addition, DIC was compared with moiré interferometry in an attempt to give future researchers guidance on which method would be appropriate for their research. Strains fields were calculated from displacement fields measured by each method. The strain fields were then compared. The main findings of the research were that: increased subset sizes caused a smoothing of data; increased step sizes reduced the resolution of the data; DIC is an accurate displacement measurement technique; the spatial resolution …
Characterization And Control Of Carbon Dioxide Seed Particle Image Velocimetry, Bartt G. Greene
Characterization And Control Of Carbon Dioxide Seed Particle Image Velocimetry, Bartt G. Greene
Theses and Dissertations
Particle Image Velocimetry (PIV) data was acquired in two separate supersonic wind tunnels with carbon dioxide (CO2) particles utilized as the seed material. Previous work in clean seeding showed CO2 could be used as seed material to produce velocity maps. This research provides the first quantitative assessment of particle response, particle size control via purge gas, and scalability using CO2 particles. A variety of feed tube and shroud configurations, in combination with varying volumetric flow rates of purge air were measured using a laser diffraction device. The CO2 particles were injected into the stilling chamber …
Demonstrative Maneuvers For Aircraft Agility Predictions, David M. Hall
Demonstrative Maneuvers For Aircraft Agility Predictions, David M. Hall
Theses and Dissertations
This study was motivated by a need to develop a reliable method of predicting the agility characteristics of various aircraft. To fully investigate the agility of an aircraft, maneuvers which push the limits of an aircraft’s maneuvering capabilities must be simulated. In these cases, classic trajectory optimization techniques either require too many assumptions for a realistic solution or require a good guess of the final solution before the problem is even attempted. This study investigated both the utility of pseudospectral optimization methods for robust trajectory optimization as well as the potential for demonstrating differences in aircraft agility characteristics of several …
Uncorrelated Track Avoidance, Darrell L. Grob
Uncorrelated Track Avoidance, Darrell L. Grob
Theses and Dissertations
The purpose of this thesis is to examine what data requirements are necessary to avoid continual series of uncorrelated tracks when gathering observations. The constants of the motion for simple two-body motion for a satellite orbiting the Earth, known as the classical orbital elements or COEs, do not remain constant due to zonal and sectoral harmonic variations in the Earth’s gravitational field. There are other elements of the motion that should be considered and this paper discusses the constancy of three elements: the Hamiltonian (H) of the Earth-Centered Rotating System, Ẑ-component of inertial angular momentum (Hk), …
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Theses and Dissertations
Within the last decade, many new technologies have significantly changed the face of private astronomy. Developments such as inexpensive but high-quality sensors, rapid personal computing, and easy networking inspire a reexamination of an old problem: how practical is it to develop initial orbit estimates for Low Earth Orbiting (LEO) satellites using optical tracking? This paper documents the design and implementation of a commercial telescope system used to answer precisely that question. This analysis deter- mined there are some challenging barriers to successful single-site orbit determination, but it is possible given the right conditions. Considering the low cost and small sup- …