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Articles 31 - 60 of 377
Full-Text Articles in Engineering
Two-Wavelength Neodymium Based Lasers, Scott H. Mccracken
Two-Wavelength Neodymium Based Lasers, Scott H. Mccracken
Theses and Dissertations
A dual wavelength Q switched laser cavity has been successfully designed and assembled to evaluate the new neodymium (Nd) based materials. Initial characterization has been achieved for Nd:YAG and Nd:YLF. The results indicate that for a fixed pulse repetition frequency, the delay time can be used to adjust the relative energy between the 1.06 and 1.32 micrometer pulses. Any deficiency in the performance of one transition can be made up by performance in the other simply by changing the relative amount of time the population inversion is allowed to build up for each pulse. The best performance was obtained using …
Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon
Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon
Theses and Dissertations
Aircraft composed of lightweight composite materials are extremely enticing since their structural weight is greatly reduced. However, the control of these aircraft is complicated by the resultant flexibility of the wings. Two avenues of approach are possible; stiffen the wings thus losing some of the weight reduction benefits, or design the lateral/directional flight control system cognizant of the wing's flexibility. In this thesis the second approach is taken. The design of three lateral/directional flight control systems for the sub-sonic flight envelope of the F-18 is presented. The Quantitative Feedback Theory (QFT) robust control design technique is used. These designs incorporate …
Optimal Formation Flight Control, Shawn B. Mccamish
Optimal Formation Flight Control, Shawn B. Mccamish
Theses and Dissertations
Automatic formation flight involves controlling multiple wing aircraft equipped with standard Mach-hold, altitude-hold, and heading-hold autopilots in order to maintain a desired position relative to a lead aircraft throughout formation maneuvers. Changes in the lead aircraft's states, including formation heading, velocity, altitude, and geometry changes, are treated as disturbance and are rejected by the formation flight control system. The work in this thesis is a continuation of five previous theses, dealing with the design of formation flight control systems. The goal of the optimal formation flight control design is to achieve robust formation maintenance in the face of formation maneuvers …
Electroencephalography: Subdural Multi-Electrode Brain Chip, John E. Rosenstengel
Electroencephalography: Subdural Multi-Electrode Brain Chip, John E. Rosenstengel
Theses and Dissertations
In October 1995, a CMOS brain chip consisting of two 8 x 17 multiplexed sub-arrays designed to measure electrical potentials at the cortical column level, was implanted on the somatosensory cortex of a laboratory rhesus monkey. Electroencephalograph (EEG) and averaged evoked response (AEG) data were taken over a period of 40 minutes. The brain chip was replaced with an identical chip, and data were again taken for 40 minutes. In both instances AEG signals of approximately 150 µVpp were recorded. Additionally, the first implanted chip recorded three phases of data: (1) AEG; (2) large clock noise (during a period …
Thermo-Mechanical Fatigue Behavior Of Cross-Ply Ceramic Matrix Composite Under Tension-Tension Loading, Dana G. Allen
Thermo-Mechanical Fatigue Behavior Of Cross-Ply Ceramic Matrix Composite Under Tension-Tension Loading, Dana G. Allen
Theses and Dissertations
The purpose of this study was to investigate the combined effect of cyclic temperature and loading on the fatigue life of a ceramic matrix composite with a cross ply lay-up. The material used in this study was a potassium borosilicate glass (BSG) doped magnesium aluminosilicate (MAS) cordierite matrix reinforced with Nicalon (silicon carbide, SiC) fibers in a [0/90]4s lay-up. Thermomechanical fatigue (TMF) tests were performed with a period of 180 seconds/cycle, or 0.00556 Hz, and a triangular wave-form. The temperature was cycled between 566°C and l093°C, and the stress levels varied between 60 MPa and 145 MPa. All tests …
Stress/Strain Ratio Effects On Fatigue Response Of A Scs-6/Ti-15-3 Metal Matrix Composite At Elevated Temperature, Sean C. Jackson
Stress/Strain Ratio Effects On Fatigue Response Of A Scs-6/Ti-15-3 Metal Matrix Composite At Elevated Temperature, Sean C. Jackson
Theses and Dissertations
This study investigated the fatigue life and damage mechanisms of a [0]8, SCS-6/Ti-15-3, metal matrix composite at 427°C for three different stress/strain ratios, R = -1, 0 and 0.5. Fatigue life and damage mechanism comparisons were made for the varying R ratios and between the load and strain control modes. Fatigue life comparisons show that on a maximum stress/strain basis as R is increased fatigue life increases while on a stress/strain range basis as R increases fatigue life decreases. Similar damage mechanisms were found between the R = -1 and R = 0 tests conducted at the same …
Frequency Effects On Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Robert N. Pittman
Frequency Effects On Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Robert N. Pittman
Theses and Dissertations
The fatigue response and life of a unidirectional SCS-6/Ti-6-4 metal-matrix composite were examined under tension-tension, load-controlled conditions at elevated temperatures and different frequencies. Composite specimens were fatigued at frequencies of 0.01, 0.1, 1 and 10 Hz, and at three stress levels. Plots of cycles to failure versus maximum stress and test frequency showed that fatigue life was more cycle-dependent at higher frequencies and more time-dependent at lower frequencies. Comparisons of tests at 427°C with their counterparts at 370°C and 538°C showed that these frequency effects were magnified as temperature increased: lower frequency tests at 538°C exhibited greater time-dependence than tests …
Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck
Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck
Theses and Dissertations
This study investigated the role base cavity depth plays in altering the overall subsonic aerodynamic forces on a free spinning axisymmetric body with wrap around fins. Wind tunnel usage allowed the forces to be monitored for varying base cavity depths and angles of attack. A base cavity depth analysis was also performed on a non-spinning axisymmetric body for comparison. Oil visualizations were conducted on the non-spinning configuration to further describe airflow patterns around the body and within the cavity. Results revealed that the aerodynamic forces, mostly drag, changed with increasing cavity depth but not to the extent previously believed. The …
Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish
Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish
Theses and Dissertations
This thesis examines the relatively new theory of nonlinear control using state dependent coefficient factorizations to mimic linear state space systems. The control theory is a nonlinear quadratic approach, analogous to linear quadratic regulation. All implementations examined in this thesis are done strictly numerically. This thesis is meant to provide a proof of concept for both satellite control and for an artificial pancreas to regulate blood glucose levels in diabetics by automatic insulin injection. These simulations represent only a first step towards practical use of the NQR method, and do not address noise rejection or robustness issues.
Evaluating The Feasibility Of Sequential Indicator Simulation In Reproducing Spatial Connectivity In A Heterogeneous Transmissivity Field, D. Duane Kenyon
Evaluating The Feasibility Of Sequential Indicator Simulation In Reproducing Spatial Connectivity In A Heterogeneous Transmissivity Field, D. Duane Kenyon
Theses and Dissertations
A Non-Parametric estimation technique was used to simulate realizations of a heterogeneous transmissivity field based upon sampled values from three different sampling scenarios. These realizations were compared to output from a parametric estimation technique with respect to truth as defined by an exhaustive data set of 6,000 transmissivity values. Estimated transmissivity fields were then used as input into a flow model from which fields of heads and specific discharges were obtained and compared. Given the financial limitations imposed upon the number and quality of samples reasonably available, Sequential Indicator Simulation, a non-parametric technique, was shown to be of considerable value …
A Comparison Of Remediation Priorities Developed By The Defense Priority Model, The Relative Risk Evaluation Method, And A Quantitative Risk Assessment Approach, David M. Hunter
Theses and Dissertations
The Superfund, established by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, seriously underestimated both the number of severely contaminated sites and the associated cleanup cost. The magnitude of projected cleanup costs, coupled with shrinking federal budgets, necessitated the development and use of risk-based prioritization models among some federal agencies. Among these tools, the DOD prioritization models are meant to give priority to sites posing the greatest threat to human health. Their failure to properly rank sites could incorrectly shift the focus from those that pose substantial risk to sites of lesser risk. The DOD site ranking …
Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert
Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert
Theses and Dissertations
As navigation systems continue to improve in performance and features, the Air Force must develop better Navigation Reference Systems (NRS) to keep pace with technology. Specifically, with the advent of enhanced, integrated Global Positioning System (GPS) and Inertial Navigation System (INS) navigators, emphasis is placed on the measuring performance in the presence of GPS jamming. To meet these needs, a new NRS, dubbed the Sub-Meter Accuracy Reference System (SARS), is being developed by the 746th Test Squadron, Holloman AFB, New Mexico. SARS uses a unique, inverted GPS pseudolite positioning system to determine a reference trajectory. This research investigates two post …
Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum
Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum
Theses and Dissertations
In response to the ever increasing accuracies in inertial navigation systems, the U. S. Air Force must develop higher accuracy reference systems. These reference systems must also be small enough to be utilized in the testing of navigation systems onboard fighter aircraft. One such proposed system utilizes carrier-phase Global Positioning System (CPGPS) transmitters mounted on MM-9 pods with receivers on the ground. This research examines one possible method of utilizing this system to determine the attitude and position of the aircraft, given position estimates for the transmitter's locations. The transmitter positioning algorithm showed that the geometry will be problematic for …
Improving The Morse Intercept Operator's Audio Display, Jesse M. Washburn
Improving The Morse Intercept Operator's Audio Display, Jesse M. Washburn
Theses and Dissertations
This thesis improves the audio display for multiple Morse communications. Factors considered to improve the audio display are frequency of source, volume level of source, and methods of unmasking. The best frequency and volume level of a Morse source is 500 Hz at 70 dB sound pressure level (spi). Two types of masking are researched: frequency masking and expectation driven masking. Experiments showed by amplifying high pitched sources the effects of frequency masking are minimized. Other methods to compensate for frequency masking are 3-D sound and the placement of a source out of phase between the ears. Morse code recognition …
Computer-Aided Diagnosis Of Mammographic Masses, William E. Polakowski
Computer-Aided Diagnosis Of Mammographic Masses, William E. Polakowski
Theses and Dissertations
A new Model-Based Vision algorithm was developed to find possibly cancerous regions of interest (ROIs) in digitized mammograms and to correctly identify the malignant masses. This work has shown a sensitivity of 92 percent for locating malignant ROIs. The database contained 272 images (12 bit, 1OO microns) with 36 malignant and 53 benign mass images. Of the 53 biopsied benign cases, 74 percent were correctly classified. The Focus of Attention (segmentation) Module algorithm used a physiologically motivated Difference of Gaussians (DoG) filter to highlight mass-like regions in the mammogram. The Index Module labeled the regions by their hypothesized class: large …
Effects Of Neutron Radiation On Resonant Cavity Light-Emitting Diodes, Daniel S. Hinkel
Effects Of Neutron Radiation On Resonant Cavity Light-Emitting Diodes, Daniel S. Hinkel
Theses and Dissertations
Resonant Cavity Light Emitting Diodes (RCLEDs) were irradiated in Ohio State University's nuclear reactor to determine the effects of Neutron displacement damage. The RCLEDs were characterized both before and after irradiation by their current versus voltage curves (I-V curves) and external light power versus current curves (L-I curves). The I-V curves showed an increase in the "knee voltage" at a neutron fluence of 1.45x1017 neutrons/cm2. Logarithmic decreases in external light power and differential quantum efficiency were observed. Significant decreases in external light power were observed at neutron fluences greater than 5.1x1013 neutrons/cm2. Equations were developed to …
A Methodology To Assess Post-Launch Efforts To Counter Mobile Tactical Ballistic Missile Launchers, Wayne H. Hayes
A Methodology To Assess Post-Launch Efforts To Counter Mobile Tactical Ballistic Missile Launchers, Wayne H. Hayes
Theses and Dissertations
The Department of Defense has a requirement to quantify the force enhancement effects from various configurations of an envisioned multilayered Theater Missile Defense (TMD) system. TMD research accomplished to date has focused primarily on the pre-launch and in-flight tactical ballistic missile (TBM) operational phases while ignoring the post-launch phase during which mobile transporter-erector-launchers (TELs) are vulnerable to attack. No methodology currently exists to measure the effectiveness of various post-launch counter-TEL system configurations or their potential contribution to the overall TMD mission. This research uses the decision analysis technique of influence diagrams to model the post-launch counter-TEL process using notional variable …
An Experimental Investigation Of A Sting-Mounted Finite Circulation Control Wing, Lorenzo C. Bradley Iii
An Experimental Investigation Of A Sting-Mounted Finite Circulation Control Wing, Lorenzo C. Bradley Iii
Theses and Dissertations
This study investigated the lift, drag and pitching moment performance of a circulation control wing in the AFIT 5-ft wind tunnel. The experimental wing model was a 20 percent thick, 8.5 percent camber, partial elliptical cross-section, single blowing slot, rectangular planform wing. The aspect ratios tested were 3.99, 3.77 and 3.75. The variables in the investigation included the slot blowing rate and model configuration. The model was modified by adding a leading edge nose droop, a trailing edge splitter plate and wing tip fences to improve flow at the leading edge, reduce separation effects, and encourage attached flow on the …
Decision Support Model For Municipal Solid Waste Management At Department Of Defense Installations, John F. Muratore
Decision Support Model For Municipal Solid Waste Management At Department Of Defense Installations, John F. Muratore
Theses and Dissertations
This research focuses on the development of a decision support model to identify the preferred strategy for managing municipal solid waste using the principles of decision analysis theory. The model provides an effective decision making tool to evaluate and compare different municipal solid waste management strategies. The users of this model, the Environmental Manager or decision maker at a given installation, can enter installation-specific waste stream characteristics, treatment and disposal costs, and material buy-back prices to determine the expected value for various alternative strategies. The strategy having the greatest expected value is considered the preferred alternative. In calculating the expected …
A Finite Element Analysis Of The Forward Rod Extrusion Process With An Emphasis On Die Profile Optimization, Mahmoud Mohamed Nagui Shatla
A Finite Element Analysis Of The Forward Rod Extrusion Process With An Emphasis On Die Profile Optimization, Mahmoud Mohamed Nagui Shatla
Archived Theses and Dissertations
No abstract provided.
Binary Gas Mixture Analysis With An Interdigitated Gate Electrode Field Effect Transistor (Igefet) Microsensor, John M. Wiseman
Binary Gas Mixture Analysis With An Interdigitated Gate Electrode Field Effect Transistor (Igefet) Microsensor, John M. Wiseman
Theses and Dissertations
Single component and binary gas mixtures of nitrogen dioxide (NO2) and ammonia (NH3) were analyzed with a microsensor composed of an array of interdigitated Gate Electrode Field Effect Transistor (IGEFET) sensor elements coated with copper-, nickel-, and cobalt-phthalocyanine thin films. Improvements in the IGEFET microsensor design and operation facilitated simultaneous measurement of ihe direct current (DC) and alternating current (AC) electrical response of the metal-substituted phthalocyanine (MPc) films to challenge gas exposure. A finite-difference model of the interdigitated gate electrode (IGE) structure confirmed the fundamental operation of the IGEFET microsensor. Principal component analysis (PCA) and multilinear regression were applied to …
Thermal Stresses In End-Heated Layered Media, Jerry R. Couick
Thermal Stresses In End-Heated Layered Media, Jerry R. Couick
Theses and Dissertations
Thermal stresses in semi-infinite layered beams heated on the end are calculated using an extension to simple bimetallic thermostat theory. Recently, researchers have used the concept of interfacial compliance to determine interlaminar stresses in a simple thermostat of finite length subjected to a uniform temperature increase. In the present work, the thermostat theory is extended to apply to the beams of interest. A closed-form solution to the problem is obtained. It is not applicable within about one beam thickness (St Venant boundary region) of the end. Various classes of layered materials are analyzed to determine if significant stresses exist outside …
Application Of Mixed-Norm Optimal Control To A Multi-Objective Active Suspension Problem, John B. Allison
Application Of Mixed-Norm Optimal Control To A Multi-Objective Active Suspension Problem, John B. Allison
Theses and Dissertations
Mixed norm optimal control synthesis is used to solve a multiobjective suspension problem. The objective is to develop a controller for an active suspension system onboard a tractor semitrailer vehicle. The problem is first approached by using H2 and H∞ optimization. It is shown that by combining both techniques into one mixed norm optimization method, it is possible to exploit the strengths of each norm to provide superior performance. Two H2/H∞ designs were completed. One design concentrated on optimal performance at one design condition. The second design concentrated on providing the best performance possible at a medium …
Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick
Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick
Theses and Dissertations
Mach 2.9 boundary layer flow (Re/m ≈ 1.75x107) under the influence of mild pressure gradients is studied numerically. Baldwin-Lomax and k - ω turbulence models are incorporated into a cell centered finite volume flow solver and the results are compared with hot wire anemometry and Laser Doppler Velocimetry (LDV) measurements obtained for the same geometries in the AFIT Mach 2.9 wind tunnel. Agreement between the present simulations obtained with the k - ω turbulence model and experimental velocity profiles is excellent in all test sections. Nondimensional turbulent shear stress predictions closely match experimental data in the …
Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan
Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan
Theses and Dissertations
Recent cut-backs in Department of Defense spending have presented a need to augment full-scale ejection seat testing with computer simulation. To this end, the U.S. Air Force's Armstrong Laboratory has developed a data set describing the Advanced Dynamic Anthropomorphic Manikin (ADAM) for use in conjunction with the Articulated Total Body (ATB) model for the purpose of simulating the dynamics of the ADAM during sled track ejections. The purpose of this thesis is to validate the ADAM data set by graphically comparing ADAM joint angular displacements calculated by the ATB model with those measured during ejection seat sled track tests. The …
Mach 2.9 Investigation Into The Flow Structure In The Vicinity Of A Wrap-Around Fin, Richard E. Huffman Jr.
Mach 2.9 Investigation Into The Flow Structure In The Vicinity Of A Wrap-Around Fin, Richard E. Huffman Jr.
Theses and Dissertations
A ceiling-mounted semi-cylindrical model containing a single wrap-around fin (WAF) was tested in the AFIT Mach 2.9 test facility. Flow visualization using oil- low streaklines, schlieren images and shadowgraph photography revealed a A-shock at the fin-body juncture and the development of an asymmetric bow-shock about the fin. Quantitative measurements were taken with a 100 cone-static pressure probe, a Pitot pressure probe and two cross-wire hot-film probes (u-v and u-w components, respectively). Measurements were made at cutting-planes from the inlet of the test section to aft of the model, with emphasis placed in the vicinity of the WAF. Results include cutting-plane …
Experimental Investigation Of A Supersonic Boundary Layer Including Favorable Pressure Gradient Effects, Joel J. Luker
Experimental Investigation Of A Supersonic Boundary Layer Including Favorable Pressure Gradient Effects, Joel J. Luker
Theses and Dissertations
This study used advanced laser Doppler velocimetry techniques to measure the turbulence intensities and Reynolds shear stresses in Mach 2.8 turbulent flat plate and Mach 2.9 favorable pressure gradient (FPG) boundary layers. The FPG was generated using a convex curved wall and had a strength of ß = 0.1, where ß is Clauser's equilibrium parameter. The maximum magnitude of the 'extra' strain rates normalized by the main strain rates was 0.1, which meant the FPG was considered to be a strong pressure gradient. The fiat plate results indicated that the LDV procedures used in this experiment prevented angular biasing of …
Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb
Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb
Theses and Dissertations
In this study mean flow and compressible turbulence measurements were taken at a station x = 72W downstream of the injection, where W is the injector throat width, of an adiabatic 2-D Mach 1.6 normal slot injection into a Mach 2.9 flow. Data were collected using a conventional Pitot probe, a cone-static probe, and multiple overheat cross-wire anemometry. In addition, schlieren and shadowgraph flow visualization was used to investigate the flow structure at both the injection point and at the downstream data collection point. From these measurements, mass flux component turbulence intensities of 8% to 10% were seen. The total …
Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis
Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis
Theses and Dissertations
This study proved that transpiration cooling provides a better cooling scheme than regenerative cooling for long operating duration, liquid-fueled rocket engine nozzles. This proof was made on the basis of maximum wall temperature. This study compared transpiration cooling to regenerative cooling in the throat region of the Space Shuttle Main Engine Main Combustion Chamber. The study also analyzed the effects of porosity, solid thermal conductivity, and porous sphere size on a porous wall made of packed spheres. The transpiration cooled nozzle operated 35% cooler than a regeneratively cooled nozzle, but the temperature gradient at the hot gas surface was 72 …
Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt
Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt
Theses and Dissertations
This study investigated the ability to control the chaotic reentry of a Delta-Clipper like vehicle by setting the values of initial arid final principal dynamical directions as well as the Lyapunov exponents. A model of the original controlled reentry vehicle was created through the use of the equations of motion in conjunction with an atmospheric model. A modified linear quadratic regulator allowed the set up of a boundary value problem which specified the Lyapunov exponents and determined the gain matrix as a function of time. The gain matrix can eventually be used in the control system of the vehicle.