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Theses and Dissertations

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Articles 9721 - 9750 of 11503

Full-Text Articles in Engineering

A Study Of Linear Vs. Nonlinear Control Techniques For The Reconfiguration Of Satellite Formations, David J. Irvin Jr. Mar 2001

A Study Of Linear Vs. Nonlinear Control Techniques For The Reconfiguration Of Satellite Formations, David J. Irvin Jr.

Theses and Dissertations

This thesis investigates several linear and nonlinear feedback control methods for satellite formation reconfigurations and compares them to a near optimal open loop, discrete-time, impulsive maneuver. The reconfigurations are done in terms of a set of relative parameters that define an orbit about the leader satellite (or center reference position if a leader satellite does not exist at the center of the formation). The purpose of the study is two-fold, to compare the control usage of continuous feedback control methods versus a discrete bum method and to determine if nonlinear control techniques offer significant improvement over more conventional linear control …

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Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser Mar 2001

Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser

Theses and Dissertations

In response to the Chernobyl nuclear power plant accident of 1986, a cesium-137 deposition dataset was assembled. Most of the airborne Chernobyl cesium was wet deposited, either via interception by falling raindrops or via absorption into cloud droplets destined to become raindrops. The Hybrid Single-Particle Lagrangian rated Transport (HYSPLIT) model, developed at Air Resources Laboratory, is used to simulate the transport and deposition of Chernobyl cesium-137. A cloud base parameterization modification is tested and appears to slightly improve the accuracy of one HYSPLIT simulation of daily Chernobyl cesium-137 deposition over the course of the accident at isolated European sites, and …

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Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein Mar 2001

Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein

Theses and Dissertations

A proposed wavelet domain communication system (WDCS) using transform domain processing is demonstrated as having enhanced interference avoidance capability under adverse environmental conditions. The WDCS system samples the environment and uses the wavelet transform, to determine interference presence and time/scale location. A digital communication waveform (basis function) is subsequently designed in the wavelet domain to specifically avoid regions containing interference. The WDCS basis function is data modulated prior to transmission. Assuming perfect synchronization, the receiver replicates a locally generated basis function for correlating with the received signal and demodulating the data. The proposed system is modeled and simulation results are …

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A Delphi Assessment Of The Digital Rosetta Stone Model, Don M. Kelley Mar 2001

A Delphi Assessment Of The Digital Rosetta Stone Model, Don M. Kelley

Theses and Dissertations

Information that is stored digitally can only be used if it can be retrieved and interpreted. if the methods to retrieve the information are lost, it may be difficult, if not impossible, to recreate them. The knowledge to interpret the bitstream is also at risk. The Digital Rosetta Stone (DRS) Model was developed as a framework for capturing and maintaining the methods necessary to retrieve and display digital information stored on obsolete media or using obsolete software. However, this conceptual model had not yet been assessed by the community of professionals for its practical efficacy. This thesis began the assessment …

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Requirements-Based Methodology For Determining Age Inventory Levels, James A. Mackenna Mar 2001

Requirements-Based Methodology For Determining Age Inventory Levels, James A. Mackenna

Theses and Dissertations

The purpose of this research was to illuminate crucial areas in analyzing AGE needs on an operational flightllne and assist in determination of AGE inventory levels. Further refinements could result in more objective and accurate assessments of actual flightline AGE needs and associated risks involved with reduction of AGE inventory levels. The research in this thesis consists of a discrete event simulation to determine desired AGE inventory level through an analysis of aircraft launches and wait time for AGE support by varying AGE (mean time between failure) MTBF and AGE inventory. Stochastic inputs for aircraft failures, AGE delivery times, and …

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Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic Mar 2001

Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic

Theses and Dissertations

This research focuses on routing of time-sensitive data in mobile ad hoc networks. Routing protocols that were developed for ad hoc networks have been reviewed. Ad Hoc On-demand Distance Vectoring (AODV) routing protocol, which is a prominent routing protocol among these protocols have been implemented in OPNET, a discrete-event simulation tool. Taking AODV as a point of departure, a routing protocol named Real Time Routing Protocol (RTRP) has been developed and also implemented in simulation environment. The performance of these routing protocols have been observed by simulating them in various experiments where the workload has been chosen to be time-sensitive …

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Lifecycle Energy And Air Emission Differences Between Electric And Internal Combustion Vehicles, David L. Mccleese Mar 2001

Lifecycle Energy And Air Emission Differences Between Electric And Internal Combustion Vehicles, David L. Mccleese

Theses and Dissertations

The U.S. Federal Government has encouraged shifting from internal combustion engine vehicles (ICEVs) to electric vehicles (EVs) with three objectives, reducing foreign oil dependence, greenhouse gas emissions, and criteria pollutant emissions. This thesis uses Monte Carlo simulation to predict lifecycle emissions and energy consumption differences per kilometer driven from replacing ICEVs with three EV options: lead acid, nickel cadmium (Ni-Cd), and nickel metal hydride (NiMH). All three EV options reduce U.S. foreign oil dependence by shifting to domestic coal. The probabilities that lifecycle energy consumption per km driven improve are lead acid 76%, Ni-Cd 64%, and NiMH 90%. The probabilities …

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Desktop Computer Programs For Preliminary Design Of Transonic Compressor Rotors, Brian C. Mcdonald Mar 2001

Desktop Computer Programs For Preliminary Design Of Transonic Compressor Rotors, Brian C. Mcdonald

Theses and Dissertations

A need exist for correlation-based desktop computer programs that predict the flow through transonic compressor rotors with nominal computational time and cost. Modified versions of two desktop computer programs, BOWSHOCK and TRANSROTOR, were used to perform a parametric study on a modem compressor rotor. BOWSHOCK calculates the exit flow properties of a supersonic streamtube through a user-defined compressor rotor. TRANSROTOR calculates flow properties at three stations in a user-defined compressor stage. Modifications to TRANSROTOR included the incorporation of a recently published rotor loss model. Baseline and modified TRANSROTOR versions were run with two modern transonic compressor blades. Results were compared …

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Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall Mar 2001

Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall

Theses and Dissertations

With the decline in military spending, the United States relies heavily on state side support. Communications has never been more important. High-quality audio and video capabilities are a must. Watermarking, traditionally used for copyright protection, is used in a new and exciting way. An efficient wavelet-based watermarking technique embeds audio information into a video signal. Several highly effective compression techniques are applied to compress the resulting audio/video signal in an embedded fashion. This wavelet-based compression algorithm incorporates bit plane coding, first difference coding, and Huffman coding. To demonstrate the potential of this audio embedding audio/video compression system, an audio signal …

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Chromate Content Bias As A Function Of Particle Size In Aircraft Primer Paint Overspray, David B. Novy Mar 2001

Chromate Content Bias As A Function Of Particle Size In Aircraft Primer Paint Overspray, David B. Novy

Theses and Dissertations

Spray painting operations using chromate-containing primer paints produce particles which may expose workers to strontium chromate. Chromate contains hexavalent chromium (Cr(VI)) which is a confirmed human carcinogen. It is suspected that the smaller particles contain disproportionately less Cr(VI) than larger particles. In order to determine if a bias in chromate content exists, paint particles were collected and separated based on particle size and the Cr(VI) concentration was determined. Aviation primer paint from the DeSoto and Deft companies was sprayed in a booth and seven-stage cascade impactors were used to separate particles.

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Air Vehicle Optimal Trajectories For Radar Exposure Minimization, Michael C. Novy Mar 2001

Air Vehicle Optimal Trajectories For Radar Exposure Minimization, Michael C. Novy

Theses and Dissertations

This study addresses the problem of analyzing the single vehicle path planning problem for radar exposure minimization. The calculus of Variations and optimal control are applied to formulate the cost function and numerical algorithms are used to solve for the optimal paths. Cost sensitivity to path length is analyzed for flight against one radar; a second radar is then included in the formulation and the optimal path for flight between the radars is found for cases of equal and unequal radar power. The costs of the optimal path, direct path, and Voronoi diagram-generated paths are compared. Results indicate low sensitivity …

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Pilot Mental Workload Calibration, Jeremy B. Noel Mar 2001

Pilot Mental Workload Calibration, Jeremy B. Noel

Theses and Dissertations

Predicting high pilot mental workload is important to the U.S. Air Force because lives and aircraft can be lost when errors are made during periods of mental overload and task saturation. Current research efforts use psychophysiological measures such as electroencephalography, cardiac, ocular, and respiration measures in an attempt to identify and predict mental workload levels. The primary focus of this effort is the development of a calibration scheme that allows a small subset of salient psychophysiological features developed using actual flight data for one pilot on a given day to accurately classify pilot mental workload for a separate pilot on …

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A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock Mar 2001

A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock

Theses and Dissertations

This study focused on multipath communication propagation impairments to the LEOSAT communications channel. Two terrain diffraction models, based on the geometric theory of diffraction (GTD), were developed and applied to the space-to-ground communications channel. These models were used to predict the impact of terrain on the performance of three LEOSAT communication systems with designs based on the Iridium, Globalstar and Orbcomm implementations. The study verified the feasibility of applying models based on the GTD rather than empirical or statistical models, to approximate the effect of propagating signals over terrain. Both models confirm that signal blockage and multipath propagation, due to …

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Estimating C-17 Operating And Support Costs: Development Of A System Dynamics Model, Christopher D. Purvis Mar 2001

Estimating C-17 Operating And Support Costs: Development Of A System Dynamics Model, Christopher D. Purvis

Theses and Dissertations

This research provides justification for experimenting with system dynamics (SD) for performing Operation and Support Cost estimates. For the C-17 Globemaster III cargo aircraft, these costs could exceed $64 billion dollars. Also, many of our weapon systems are beginning to reach the end of their effective life span, and discussions about the impact of aging, on aircraft, has become a hot topic in the literature. System Dynamics is a modeling methodology developed in 1958, but never used extensively for cost estimating. SD offers unique capabilities to the cost estimator, including the ability to model causal relationships. This capability offers the …

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Phugoid Damping Control, Nicolas J. Schindeler Mar 2001

Phugoid Damping Control, Nicolas J. Schindeler

Theses and Dissertations

A novel phugoid damping control design methodology is developed, based on the use of wind axes and a point-mass aircraft model. The state variables are air speed, flight path angle, and heading angle, the control variables are thrust setting, angle of attack, bank angle, and sideslip angle, and the command signals are airspeed, flight path angle, and heading angle or heading rate. All the variables and parameters are nondimensionalized. A multivariable set point controller is developed which consists of: (1) a trim calculation-based nonlinear feed-forward control computer; thus, given a commanded new trim state (air speed, flight path angle, and …

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Concept Exploration Of An Australian Indigenous Space Launch Capability, Anthony J. Rogers Mar 2001

Concept Exploration Of An Australian Indigenous Space Launch Capability, Anthony J. Rogers

Theses and Dissertations

This thesis explores the possibility of establishing an Australian indigenous space launch capability through developing and examining an Australian space launch program model. The model is based around launch site location, vehicle design, program duration, and the percentage Australian indigenous input into the program. The model was optimised in an effort maximise the benefits of such a capability, namely political prestige, security and in country technological base, while minimising the program's overall cost.

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A Model For Palladium Catalyzed Destruction Of Chlorinated Ethenes In Contaminated Groundwater, Christopher M. Stoppel Mar 2001

A Model For Palladium Catalyzed Destruction Of Chlorinated Ethenes In Contaminated Groundwater, Christopher M. Stoppel

Theses and Dissertations

Groundwater contamination by chlorinated ethenes is a widespread environmental problem. Conventional remediation technologies have shortcomings that have prompted further research into the development of novel treatment technologies. A palladium/ alumina catalyst in the presence of dissolved molecular hydrogen (referred to hereafter as a PD/H2 system) has been demonstrated to rapidly destroy chlorinated ethene contaminated groundwater. First-order kinetics have been used to model chlorinated ethene destruction in a PD/H2 reactor. However, catalyst deactivation and regeneration are important processes that also need to be modeled in order to better understand their effect on treatment efficiency. This study presents a model …

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Gss Technology As A Moderator Of Influence And Perceived Expertise, Kevin V. Thompson Mar 2001

Gss Technology As A Moderator Of Influence And Perceived Expertise, Kevin V. Thompson

Theses and Dissertations

Group Support System (355) research has found this content and process anonymity influence problem solving groups. However, previous studies report mixed results on how OSS technology changes social influence processes and recognition of expertise which affect group performance. This thesis explored content and process anonymity's affect on influence and perceived expertise using three treatments to derive possible explanations for the mixed results found in previous GSS research. The study developed a theoretical model of influence, perceived expertise, and performance. Using structural equation modeling the study tested the relationships between expertise and participation rates, and overall group performance. An experiment was …

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Decision Analysis Methodology To Evaluate Integrated Solid Waste Management Alternatives For A Remote Alaskan Air Station, Mark J. Shoviak Mar 2001

Decision Analysis Methodology To Evaluate Integrated Solid Waste Management Alternatives For A Remote Alaskan Air Station, Mark J. Shoviak

Theses and Dissertations

Eareckson Air Station (AS), a remote U.S. Air Force installation, faces the complex decision of selecting a new municipal solid waste (MSW) management strategy to replace its current non-compliant system. This research effort applies value-focused thinking and multiattribute preference theory to decision analysis techniques to produce a multiple-objective decision analysis model that captures all of the site's MSW goals, objectives, and concerns in order to facilitate the evaluation of MSW management strategies available. The model ranks 40 specific MSW management alternatives, which were developed in accordance with the decision-maker's assumptions and constraints, based on how well they meet Eareckson's overall …

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Relating Initial Budget To Program Growth With Rayleigh And Weibull Models, Eric J. Unger Mar 2001

Relating Initial Budget To Program Growth With Rayleigh And Weibull Models, Eric J. Unger

Theses and Dissertations

Previous research on completed defense R&D shows that contract expenditures can be fit well with a Rayleigh model. With fixed outlay rates, as prescribed by the OSD comptroller, the budget profile must have most of the funds in the early years to produce Rayleigh-distributed expenditures. R&D programs with more delayed funding profiles may also produce expenditures that a Rayleigh model fits through schedule slips and cost overruns. This research tests how well the initial funding profile produces Rayleigh-distributed expenditures that can be related to the program's final cost overrun and schedule slips. Based only on the initial budget profile, we …

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Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas Mar 2001

Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas

Theses and Dissertations

With the rise of mobile computing and an increasing need for ubiquitous high speed data connections, Internet-in-the-sky solutions are becoming increasingly viable. To reduce the network overhead of one-to-many transmissions, the multicast protocol has been devised. The implementation of multicast in these Low Earth Orbit (LEO) constellations is a critical component to achieving an omnipresent network environment. This research examines the system performance associated with two terrestrial-based multicast mobility solutions, Distance Vector Multicast Routing Protocol (DVMRP) with mobile IP and On Demand Multicast Routing Protocol (ODMRP). These protocols are implemented and simulated in a six plane, 66 satellite LEO constellation. …

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Computational Investigation Of Aeromechanical Hcf Effects In A Compressor Rotor, Andrew L. White Mar 2001

Computational Investigation Of Aeromechanical Hcf Effects In A Compressor Rotor, Andrew L. White

Theses and Dissertations

High-Cycle Fatigue is a major problem facing the gas turbine industry today. It has been investigated by many researchers, using many different methods. Due to its highly complex nature, designers still do not have adequate tools to accurately predict the onset of high-cycle fatigue. A three-dimensional Navier-Stokes program was used to perform a study of the unsteady aerodynamics on a compressor rotor. The effect of aerodynamic detuning on the forced response of a rotor blade was compared to a baseline tuned rotor case. Detuning consisted of a ten percent decrease in circumferential spacing between alternate pairs of blades. The high-cycle …

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Microdot-A 4-Bit Synchronous Microcontroller For Space Applications, Kirby M. Watson Mar 2001

Microdot-A 4-Bit Synchronous Microcontroller For Space Applications, Kirby M. Watson

Theses and Dissertations

Satellites have limited power budgets due to the amount of power collected by the satellite's solar panels. The goal is to have a wide range of functionality, while running off a limited power source. Large microprocessors use large amounts of power to report back temperature and chemical sensor data to ground stations. By using small micro controllers to perform the data collection and minimizing the usage of the larger microprocessors, the satellites will save power. A prototype design of the Microdot 4-bit micro controller for space applications is presented. Requirements for the Microdot, such as microwatt power consumption and 23 …

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Identifying Demand Indicators For Air Force Recruiting Service With Discriminant Analysis, Jason L. Williams Mar 2001

Identifying Demand Indicators For Air Force Recruiting Service With Discriminant Analysis, Jason L. Williams

Theses and Dissertations

A changing public disposition towards military service has all four military branches rethinking recruiting practices. This Air Force is reacting to this new recruiting climate by increasing the bonuses for new recruits, pumping up advertising budgets, and bolstering recruiting personnel levels. This thesis provides a new tool for assessing how to allocate these new resources. Discriminant Analysis is used to identify population characteristics that categorize recruiting locations. A methodology is constructed that can discriminate between communities where interest is high in military service and where recruiting efforts will not be productive.

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Routing Unmanned Aerial Vehicles While Considering General Restricted Operating Zones, Darin T. Brown Mar 2001

Routing Unmanned Aerial Vehicles While Considering General Restricted Operating Zones, Darin T. Brown

Theses and Dissertations

U.S. military forces employ unmanned aerial vehicles (UAVs) to conduct intelligence-gathering missions worldwide. For a typical mission, commanders may task UAV operators to gather imagery on 100 or more sites or targets. UAV operators must quickly prepare mission plans that meet the needs of their commanders while dealing with real-world constraints such as time windows, site priorities, imagery requirements, UAVs with different capabilities (i.e. imagery equipment, speed, and range), and UAVs departing from different bases. Previous AFIT research provided the UAV Battlelab with a tool, AFIT Router, for generating high-quality routes to aid mission planning. This research enhances the AFIT …

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Image Registration Using Redundant Wavelet Transforms, Richard K. Brown Mar 2001

Image Registration Using Redundant Wavelet Transforms, Richard K. Brown

Theses and Dissertations

Imagery is collected much faster and in significantly greater quantities today compared to a few years ago. Accurate registration of this imagery is vital for comparing the similarities and differences between multiple images. Since human analysis is tedious and error prone for large data sets, we require an automatic, efficient, robust, and accurate method to register images. Wavelet transforms have proven useful for a variety of signal and image processing tasks, including image registration. In our research, we present a fundamentally new wavelet-based registration algorithm utilizing redundant transforms and a masking process to suppress the adverse effects of noise and …

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A Multi-Objective Decision Support Model For The Turkish Armed Forces Personnel Assignment System, Zubeyir Cimen Mar 2001

A Multi-Objective Decision Support Model For The Turkish Armed Forces Personnel Assignment System, Zubeyir Cimen

Theses and Dissertations

The Turkish Armed Forces (TAF) assign more than 25,000 active duty personnel annually. TAF wants to obtain maximum utilization of its personnel by assigning the right person to the right job at the right time, To accomplish this task, decision-makers and personnel assignment staff should consider conflicting multiple objectives that create the widely known problem called "personnel assignment problem". To assist in this complicated task from a quantitative perspective, a preemptive goal programming approach was used to develop an integer programming (IP) model to capture the multiple objectives flexibly and interactively. A realistic size IP problem with random data was …

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An Identification And Discussion Of Key Success Factors In The Acquisition Of Commercial-Off-The-Shelf (Cots-) Based Systems, John F. Corbett Mar 2001

An Identification And Discussion Of Key Success Factors In The Acquisition Of Commercial-Off-The-Shelf (Cots-) Based Systems, John F. Corbett

Theses and Dissertations

The purpose of this research was to explore COTS-based systems as they are acquired by the Air Force. Current guidance related to the acquisition of COTS-based systems is explored. Based upon the literature reviewed, the research targeted the specific area of acquisition plans. A multiple case study of acquisition plans from several COTS-based systems was performed. Current guidance related to the acquisition plan has not been specifically tailored to COTS-based systems. The results of the analysis of the COTS-based systems showed that the use total ownership cost (TOC) and cost as an independent variable (CAIV) enabled a system to he …

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An Analysis Of Civil Engineer Officer Contingency Training, Rusty J. Vaira Mar 2001

An Analysis Of Civil Engineer Officer Contingency Training, Rusty J. Vaira

Theses and Dissertations

The primary objective of this research was to investigate the current overall civil engineer officer contingency training program and determine if civil engineer officers think it is adequately preparing them to perform in a contingency environment. In accomplishing this objective, this research explored the perceptions that officers have about the contingency training that is available through three primary training programs (Home Station Training, Silver Flag training, and Civil Engineer and Services School training). The overall intent of the author was to gauge how the officers feel about their contingency training and offer some suggestions on how to improve the training. …

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Assessment Of The Effects Of Entrainment And Wind Shear On Nuclear Cloud Rise Modeling, Daniel E. Zalewski Mar 2001

Assessment Of The Effects Of Entrainment And Wind Shear On Nuclear Cloud Rise Modeling, Daniel E. Zalewski

Theses and Dissertations

The Missile Defense Agency (MDA) plans to construct, during a two-week period, an X-Band Radar (XBR) on Shemya, AK. Wind speeds must not, at any time during the construction, exceed a 25 knot limit set by the MDA for lifting the massive dome panels into place. The goal of this research was to explore the possibilities of long-range forecasts to determine the feasibility of predicting any upcoming two-week windows of opportunity, well in advance, that will ensure the successful completion of constructing the XBR on Shemya. In order to reach this goal, the following objectives were achieved; (1) a climatological …

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