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Theses and Dissertations

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Articles 1411 - 1440 of 1780

Full-Text Articles in Aerospace Engineering

A Comparative Analysis Of The Iridium® And Globalstar® Satellite Transmission Paths, Kenneth E. Crowe Mar 1999

A Comparative Analysis Of The Iridium® And Globalstar® Satellite Transmission Paths, Kenneth E. Crowe

Theses and Dissertations

Globalstar and Iridium will provide valuable global communications assets for business, humanitarian aid and military operations. However, the level of coverage and the quality of the transmission path of these systems are strongly dependent on the latitude of the user and, due to their orbital characteristics, both systems provide reduced levels of coverage at low latitudes. Additionally, the L- and S-Band frequencies utilized by these systems are prone to ionospheric interference at low latitudes. The results of extensive simulation analysis indicate that the Globalstar constellation architecture provides a considerably better transmission path than Iridium's in several important areas, including path …

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Space Maneuver Vehicle Orbital Mission Planner: Development Of Application And Analysis Of On-Demand Maneuvering Ability, Shon P. Williams Mar 1999

Space Maneuver Vehicle Orbital Mission Planner: Development Of Application And Analysis Of On-Demand Maneuvering Ability, Shon P. Williams

Theses and Dissertations

The USAF has developed the Space Maneuver Vehicle (SMV) to fulfill the requirement for flexibility, rapid response, and on-demand maneuverability of space assets. This reusable satellite merges the efficiency and readiness of aircraft-like operations with the capability of global coverage from space. Designed to provide over 10,500 fps of velocity change (or delta-v) while in orbit, the SMV out-maneuvers existing satellites by up to 100 times. This thesis helps transition the SMV to the operational area by demonstrating their responsiveness to varied mission taskings. The SMV Orbital Mission Planner allows the operator to place any number of SMVs in orbit …

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Whole Spacecraft Vibration Isolation, Gregory G. Karahalis Mar 1999

Whole Spacecraft Vibration Isolation, Gregory G. Karahalis

Theses and Dissertations

The Department of Defense identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance the reliability, lifetime, and payload to structure ratio. DoD satellite programs stand to benefit significantly from advances in vibration isolation technology.

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Design Of The Computer Subsystem For The Afit Simulation Satellite (Simsat), Michael P. Hanke Dec 1998

Design Of The Computer Subsystem For The Afit Simulation Satellite (Simsat), Michael P. Hanke

Theses and Dissertations

This document details the systematic development of the computer subsystem for the AFIT Simulation Satellite (SIMSAT) from Concept Exploration to Implementation. This subsystem design effort was conducted as part of a larger four-phase team design effort to implement a fully functional, user-friendly test facility to meet current AFIT teaching and research requirements. Once SIMSAT system integration is complete, control laws will execute on the free-floating "satellite" to reduce communication systems overhead and its impact on control law execution, thereby allowing for more robust control system development and execution. Control law development, simulation, and interactive control of the system will occur …

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Electro-Mechanical Fatigue Behavior Of A Quasi-Isotropic Laminate With An Embedded Piezoelectric Actuator, Tse Lin Hsu Sep 1998

Electro-Mechanical Fatigue Behavior Of A Quasi-Isotropic Laminate With An Embedded Piezoelectric Actuator, Tse Lin Hsu

Theses and Dissertations

This study primarily investigated the electro-mechanical fatigue behavior of the embedded piezoelectric actuators in graphite/epoxy laminate with a lay-up of 0 | ± 45 | 90s. A secondary focus was the investigation of the mechanical fatigue effects of the 0 | 0 | ± 45 | 0 | 0 | 90s laminate with embedded PZT under tensile loading. All the fatigue tests were conducted with a triangular loading waveform which had a frequency of 10 Hz and with R=0. 1. In the electro-mechanical testing, the embedded actuator was excited by a -10 V to -100 V or a 10 V …

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Wind Tunnel Testing For Drag Reduction Of An Aircraft Laser Turret, Christopher H. Snyder Jun 1998

Wind Tunnel Testing For Drag Reduction Of An Aircraft Laser Turret, Christopher H. Snyder

Theses and Dissertations

This study investigated the use of aft-mounted fairings and splitter plates to reduce the drag of a half-scale aircraft laser turret. Forces, moments, and pressure distributions were measured in the AFIT 1.5-m (5-ft) wind tunnel at Reynolds numbers between 3x105 and 9x105 based on the turret diameter. Oil traces indicated the nature of the flow near the surface of the unmodified turret and the surrounding area. Tufts placed on the turret, fairings, and splitter plates showed changes in separation regions when configurations were changed. The flow around the turret was characterized by dominant vortices shedding from the top …

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Singularity Avoidance Strategies For Satellite Mounted Manipulators Using Attitude Control, Nathan A. Titus Jun 1998

Singularity Avoidance Strategies For Satellite Mounted Manipulators Using Attitude Control, Nathan A. Titus

Theses and Dissertations

Control concepts for satellite mounted manipulators (SMM) are examined. The primary focus is on base actuated concepts, which eliminate singularity problems associated with free floating SMMs. A new form of the equations of motion for an n-link SMM is developed using a quasi coordinate form of Lagrange's Equation. Alternative free floating SMM designs are presented which eliminate dynamic singularities, but still experience difficulties due to the unactuated base. A new generic SMM controller is developed as a framework for various control concepts with and without base actuation. Momentum constrained Jacobians are shown to produce better SMM tracking than fixed base …

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Improved Mathematical Modeling For Gps Based Navigation, Salvatore Nardi Mar 1998

Improved Mathematical Modeling For Gps Based Navigation, Salvatore Nardi

Theses and Dissertations

This thesis is concerned with the development of new closed form GPS position determination algorithms that work in the presence of pseudorange measurement noise. The mathematical derivation of two closed form algorithms, based on stochastic modeling and estimation techniques, is presented. The algorithms provide an estimate of the GPS solution parameters (viz., the user position and the user clock bias) as well as the estimation error covariance. The experimental results are analyzed by comparison to the baseline results from the conventional Iterative Least Squares (ILS) algorithm. In typical GPS scenarios, the closed form algorithms are extremely sensitive to noise, making …

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Optimizing The Efficiency Of A Multi-Stage Axial-Flow Compressor: An Application Of Stage-Wise Optimization, Shawn A. Miller Mar 1998

Optimizing The Efficiency Of A Multi-Stage Axial-Flow Compressor: An Application Of Stage-Wise Optimization, Shawn A. Miller

Theses and Dissertations

The development of jet engines has become an integral part of maintaining air superiority. In order to achieve the most advanced engine, research has turned to traditional optimization methods to aid in creating new engine designs. To develop simplified mathematical models representative of the engine, the engine can be separated into its components. A jet engine has three major elements, the compressor, combustion chamber and turbine. This research attempts to make an initial analysis of a two stage compressor to determine values of blade angles and spacing to chord ratios for both stages that produce the highest possible efficiency for …

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A Variable-Complexity Modeling Approach To Scramjet Fuel Injection Array Design Optimization, Michael D. Payne Mar 1998

A Variable-Complexity Modeling Approach To Scramjet Fuel Injection Array Design Optimization, Michael D. Payne

Theses and Dissertations

The analysis of fuel air mixing in a scramjet is often accomplished either with Computational Fluid Dynamics (CFD) algorithms or through experimental research. These approaches, while accurate and reliable, are extremely expensive and thus not well suited for use with conventional design optimization methods. In this investigation, Variable Complexity Modeling (VCM) is used to significantly reduce the number of complex, expensive analyses required to optimize the design of a scramjet fuel injection array. A design problem formulation for a lateral transverse injection array is developed and a VCM approach to design optimization is conducted in two stages. Initially, a simplified …

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Damage Detection Using Pattern Classifiers, Eric D. Swenson Mar 1998

Damage Detection Using Pattern Classifiers, Eric D. Swenson

Theses and Dissertations

The research focused on developing and tuning finite element models to train pattern classifiers to detect and locate damage in a real structure. The research was broken into three distinct phases: finite element (FE) model development, FE model tuning, and pattern classifier training and testing. In the finite element development phase, a low order FE model called the baseline model and a high order model called the stiff model were created. In the FE model tuning phase, these FE models were tuned using measured Frequency Response Functions (FRFs), and the results were compared with previous research in which tuning was …

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The Influence Of Surface Roughness On Supersonic High Reynolds Number Turbulent Boundary Layer Flow, Robert M. Latin Mar 1998

The Influence Of Surface Roughness On Supersonic High Reynolds Number Turbulent Boundary Layer Flow, Robert M. Latin

Theses and Dissertations

A comprehensive study of rough-wall high speed (M=2.9) high Reynolds number (Re/m = 1.9 x 107) turbulent boundary layer flow was performed consisting of experimental, analytical, and numerical methods. Six wall topologies consisting of a smooth and five rough surfaces (two and three dimensional machined roughness plates; and 80, 36, and 20 grit sand-grain roughened plates) were studied. A confocal laser scan microscope was used to measure the topography of the sand grain roughnesses. The experimental measurement techniques included a convention Pitot pressure probe, laser Doppler velocimetry, hot wire anemometry; color schlieren and laser …

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Analysis Of Turbulence Models As Applied To Two- And Three-Dimensional Injection Flows, Clarence R. Chenault Mar 1998

Analysis Of Turbulence Models As Applied To Two- And Three-Dimensional Injection Flows, Clarence R. Chenault

Theses and Dissertations

A steady state solution of the full, three dimensional Favre averaged Navier Stokes equations, coupled with a second order Reynolds stress turbulence model (RSTM) and an eddy viscosity model were used to numerically simulate oblique injection into supersonic flow. Numerical results were compared to experimental data and the turbulence models were evaluated for accurate prediction of thermomechanical mean flow variables, Reynolds stresses, flowfield shock structure and boundary layer phenomena. The RSTM simulation resulted in physically consistent and accurate predictions for the mean flow and turbulent quantities. Simulations with the eddy viscosity model resulted in non-physical and inconsistent turbulence predictions. RSTM …

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An Evaluation Of Frequency Domain Ensemble Averaging To Improve Aircraft Stability Derivative Estimation, Lawrence M. Hoffman Mar 1998

An Evaluation Of Frequency Domain Ensemble Averaging To Improve Aircraft Stability Derivative Estimation, Lawrence M. Hoffman

Theses and Dissertations

This research evaluated a process to improve aircraft stability derivative estimation results. The Have Derivatives process used overlap ensemble averaging in the frequency domain to minimize noise on the original time domain signals. The process estimated average complex frequency response functions that were then transformed back into the time domain as a set of discrete pulse responses with far less noise than the original signals. These clean signals were used in a parameter estimation program to estimate better stability derivatives than were estimated with the original noisy signals. Both simulation and flight test data were used to study the effects …

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Effect Of High Free Stream Turbulence On Film Cooling Using Double Row Of 30° Slant-Hole Injectors, Lilith I. Sorensen Mar 1998

Effect Of High Free Stream Turbulence On Film Cooling Using Double Row Of 30° Slant-Hole Injectors, Lilith I. Sorensen

Theses and Dissertations

In this study free stream turbulence levels from 7.3% to 17.8% are applied to film cooling over a flat plate with two rows of 30° slant holes using a wall jet as the main stream air supply and source of turbulence. Blowing ratios are varied from 0.25 to 2.0 and free stream velocities at injection range from 10 m/s to 85 m/s. A constant density ratio of 1.07 is kept throughout the experiment. Results show that for different magnitudes of blowing ratio free stream turbulence has a different influence on effectiveness. At the forward stations, where blow off was present …

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Flight Test And Handling Qualities Analysis Of A Longitudinal Flight Control System Using Multiobjective Techniques, John R. Anderson Mar 1998

Flight Test And Handling Qualities Analysis Of A Longitudinal Flight Control System Using Multiobjective Techniques, John R. Anderson

Theses and Dissertations

This thesis addresses the application of optimal, multiobjective control theory control theory to flight control design for the approach and landing phase of flight. Five flight control systems were designed using classical, H2, H infinity, and Mixed H2/H infinity methods. The MATLAB™ MUTOOLS™ and AFIT MXTOOLS toolboxes were used to produce the optimal, multiobjective designs. These designs were implemented for flight test on the Calspan VSS I Learjet, simulating the unstable longitudinal dynamics of an F-16 type aircraft. A limited handling qualities investigation was performed. Model following was used in the design phase to meet handling qualities specifications. The designs …

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Orbit Estimation Using Track Compression And Least Squares Differential Correction, Vincent J. Chioma Dec 1997

Orbit Estimation Using Track Compression And Least Squares Differential Correction, Vincent J. Chioma

Theses and Dissertations

This thesis develops two methods of compressing a track of radar observations of a satellite into a single state vector and associated covariance matrix, and a method of estimating orbits using results from multiple tracks. The track compression uses least squares differential correction to determine a state vector at the central observation time. The resulting state vectors and covariance matrices are then used to estimate the satellite's orbit, also using least squares differential correction. Numerical integration using two-body, J2 and an atmospheric drag model is used to represent the dynamics. This orbit estimation produces a state vector which includes …

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Flow Field And Loading Analysis On A Wrap-Around Fin Missile, Thomas C. Mcintyre Dec 1997

Flow Field And Loading Analysis On A Wrap-Around Fin Missile, Thomas C. Mcintyre

Theses and Dissertations

Wrap-around fin (WAF) missiles offer packaging benefits but experience rolling moments due to the curved fin design. Rolling moments stabilize unguided projectiles, but cause guidance and control problems for future guided applications. Understanding the flow field in the vicinity of the fins is critical to future missiles. Fin pressure profiles were characterized with pressure-sensitive paint. Two rectangular four-fin constructions were tested-one solid and one with a rectangular hole (slotted fin). Static pressure data were divided by free-stream total pressure for presentation. Tests were conducted at Mach numbers of 2.15, 2.28, 2.41, 2.86, 3.25, 3.50 and 3.83. Reynolds numbers based on …

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Effects Of Liquid Transpiration Cooling On Heat Transfer To The Diverging Region Of A Porous-Walled Nozzle, Daniel J. Schieb Dec 1997

Effects Of Liquid Transpiration Cooling On Heat Transfer To The Diverging Region Of A Porous-Walled Nozzle, Daniel J. Schieb

Theses and Dissertations

This research effort investigated the effects of evaporation of water on the heat transferred to the wall of the diverging portion of a porous walled nozzle The AFIT High Pressure Shock Tube was used with a two-dimensional Mach 3 nozzle. One flat surface of the nozzle was fitted with a layer of porous stainless steel from the nozzle throat to the exit. This porous material was saturated with water to simulate liquid transpiration cooling. Surface temperature data was taken in this region using fast response coaxial thermocouple. Heat transfer was determined from the surface temperature history. Data was taken for …

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Optimal Non-Coplanar Launch To Quick Rendezvous, Gregory B. Sears Dec 1997

Optimal Non-Coplanar Launch To Quick Rendezvous, Gregory B. Sears

Theses and Dissertations

The purpose of this study was to determine the feasibility of launching a Delta Clipper-like vehicle on an optimal, non-coplanar trajectory to rendezvous with an earth orbiting object in one orbit or less. The focus of the research was to determine what such a trajectory would look like, and to determine the cost, in payload mass, of flying such a trajectory. A model for the ascent trajectory was developed using the dynamics equations of motion, an atmosphere model, and an aerodynamic model for the DC-Y concept vehicle. A boundary value problem was posed and solved for a coplanar rendezvous. The …

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Constrained Model Predictive Control Of A Nonlinear Aerospace System, Christopher M. Shearer Dec 1997

Constrained Model Predictive Control Of A Nonlinear Aerospace System, Christopher M. Shearer

Theses and Dissertations

Recent research efforts have applied the receding horizon Model Predictive Control (MPC) strategy to linearized high performance aerospace systems. The research contained in this thesis used these recent results in order to apply the MPC strategy to a nonlinear high performance aerospace system, specifically an F-16 fighter aircraft model. The model was commanded to follow dynamic trajectories of roll angle and altitude. Further, adaptive constraint techniques were used to improve system tracking. To accomplish these tasks, code and block diagrams were generated using the commercial software packages of Matlab and Simulink. Numerous simulations were conducted with the goal of achieving …

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Space Shuttle East Coast Abort Modes For High Inclination Launches, Richard K. Neufang Dec 1997

Space Shuttle East Coast Abort Modes For High Inclination Launches, Richard K. Neufang

Theses and Dissertations

This study investigated the possibility of abort landing the Space Shuttle at east coast airports when launched at inclinations of 51.6 degrees or more. Computer modeling was used to characterize both the Shuttle launch out of Cape Canaveral and two methods of unpowered abort descents from various points in the launch following Solid Rocket Booster SRB separation. The first method used varying values of pitch and roll held constant to control the descent. By plotting the latitude and longitude of the point in the descent when the nominal landing altitude was achieved against locations of east coast airports it was …

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Warning Times And Impact Predictions Of Asteroids And Comets On A Collision Course With Earth, Ahren D. Heidt Dec 1997

Warning Times And Impact Predictions Of Asteroids And Comets On A Collision Course With Earth, Ahren D. Heidt

Theses and Dissertations

This study investigates the amount of data and time necessary to accurately predict Earth impacts of Earth Crossing Objects (ECOs). Trajectories are simulated by numerically integrating in an N-Body system. Given final impact parameters, the trajectory is propagated backwards to an earlier time, creating initial conditions and simulated observation data at requested intervals to which Gaussian random noise is introduced. Utilizing a Bayes Filter to estimate position and velocity from the simulated observation data, the estimate is then propagated forward in time to determine whether or not an impact can be accurately predicted. State vectors and covariance matrices are then …

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Optimal Orbit Insertion Strategies Using Combined High And Low Thrust Propulsion Systems, Darren W. Johnson Dec 1997

Optimal Orbit Insertion Strategies Using Combined High And Low Thrust Propulsion Systems, Darren W. Johnson

Theses and Dissertations

Low thrust electric propulsion systems are becoming sufficiently mature to consider their use as primary propulsion for orbital transfer in place of high thrust chemical systems. Instead of facing an either/or situation, it may be advantageous to use both types. This effort demonstrates a technique for finding orbital transfer strategies that use both high and low thrust propulsion systems and which result in optimal tradeoffs of the performance parameters cost of orbit insertion, total orbit transfer time, and available spacecraft mass at final orbit. These performance parameters are calculated as a function of the fraction of orbit transfer from Low …

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Pseudorandom Code Generation For Communication And Navigation System Applications, John F. Brendle Jr. Dec 1997

Pseudorandom Code Generation For Communication And Navigation System Applications, John F. Brendle Jr.

Theses and Dissertations

This research project investigated the design, construction and evaluation of a pseudorandom code generator for communication and navigation system applications. These types of codes include spreading codes, Gold codes, Jet Propulsion Laboratory (JPL) ranging codes, syncopated codes, and nonlinear codes. Such waveforms are typically used in communication and navigation system applications. The code generator uses the Stanford Telecom STEL-1032 Pseudorandom Number (PRN) coder. A coder interface was designed and constructed for manual data entry to the registers of the PRN coder. The code generator is capable of independently clocking and generating all possible codes with lengths up to 4,294,967,295 bits. …

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Velocity Profiles And Skin Friction On A Ribletted Flat Plate In Adverse Pressure Gradient, Richard D. Branam Dec 1997

Velocity Profiles And Skin Friction On A Ribletted Flat Plate In Adverse Pressure Gradient, Richard D. Branam

Theses and Dissertations

This project investigated the flow field characteristics over a flat, ribletted plate and the effects of an adverse pressure gradient on this flow field. Testing examined the development of the flow over the ribletted plate from laminar through fully turbulent flow fields. The flow field states (laminar, transitional, and turbulent) were determined using local turbulence intensity values and boundary layer profiles. Several parameters were examined to help better describe the flow characteristics, boundary layer profiles, and influence on skin friction drag. The skin friction drag coefficients were calculated using a numerical integration technique to determine an average value and scaled …

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Development And Validation Of An Experimental Test Rig For Electrohydrodynamic Enhancement Of Forced Convective Heat Transfer, William T. Caldwell Dec 1997

Development And Validation Of An Experimental Test Rig For Electrohydrodynamic Enhancement Of Forced Convective Heat Transfer, William T. Caldwell

Theses and Dissertations

This report details the development of a facility for the experimental investigation of electrohydrodynamic (EHD) enhancement of forced convection heat transfer. The test facility was developed for the Thermal and Transparencies Laboratory (TATLAB), Air Force Research Laboratory (AFRL), for use in future research into the applicability of EHD for the miniaturization of Air Force heat exchangers. During this research, a closed l6op, medium scale electrohydrodynamic test rig was developed and brought online. The test fluid loop was integrated with a data acquisition and parameter control system. Basic loop and fluid performance testing was accomplished through the use of a 3mm …

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Multiple Model Adaptive Estimation And Control Redistribution Performance On The Vista F-16 During Partial Actuator Impairments, Curtis S. Clark Dec 1997

Multiple Model Adaptive Estimation And Control Redistribution Performance On The Vista F-16 During Partial Actuator Impairments, Curtis S. Clark

Theses and Dissertations

Multiple Model Adaptive Estimation with Control Reconfiguration (MMAE/CR) capability to estimate and compensate for partial actuator failures, or "impairments" is investigated using the high-fidelity, nonlinear, six-degree-of-freedom, VISTA F-16 simulation which currently resides on the Simulation Rapid-Prototyping Facility (SRF). After developing a model for inserting partial actuator impairments into the VISTA F-16 truth model, research begins with a battery of single actuator impairment tests. This stage of research explores the capability of the existing MMAE algorithm to estimate single, partial actuator impairments, and helps to define refinements and expansions needed in the MMAE algorithm for the second phase of research: the …

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Satellite Integrated Power And Attitude Control System Design Study, Stephen A. Fischer, Dwight D. Fullingim, Brian L. James, James M. Valenti, Jorg D. Walter, Paul J. Cotter, William A. Seeliger Dec 1997

Satellite Integrated Power And Attitude Control System Design Study, Stephen A. Fischer, Dwight D. Fullingim, Brian L. James, James M. Valenti, Jorg D. Walter, Paul J. Cotter, William A. Seeliger

Theses and Dissertations

Technological advances have brought Flywheel Energy Storage (FES) systems to the point where they can be used in satellites as replacements for chemical batteries. Flywheels have characteristics that may overcome limitations inherent in batteries. These characteristics include high specific energy, minimal degradation over time, and precise knowledge of charge level. A further advantage of flywheels is that, in a combined system, they can be used to replace traditional attitude control hardware. These Integrated Power and Attitude Control Systems (IPACS) show the potential to have less mass than the systems they replace. The question this study seeks to answer is, "In …

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Experimental Investigation Of The Influence Of Molecular Weight On Mixing And Penetration In Supersonic Dissimilar Gaseous Injection Into A Supersonic Cross-Flow, Troy A. Giese Dec 1997

Experimental Investigation Of The Influence Of Molecular Weight On Mixing And Penetration In Supersonic Dissimilar Gaseous Injection Into A Supersonic Cross-Flow, Troy A. Giese

Theses and Dissertations

In pursuit of a more efficient and effective fuel-air mixing for a SCRAMjet combustor, this study investigated relative near field effects of molecular weight on mixing and penetration of different gaseous injection into a supersonic (M=2.9) cross flow. Helium and argon gas were chosen as injectants because of the large differences in molecular weights. Also, mixing enhancement was observed by injecting the traverse gas jet parallel to the compression face of a ramp. Color schlieren photography was used to identify the shock structures and interactions in the flow field. Measurements of mean flow properties were used to establish the jet …

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