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Articles 9031 - 9060 of 11121

Full-Text Articles in Engineering

Micro Synthetic Jets As Effective Actuator, Mehti Koklu Apr 2007

Micro Synthetic Jets As Effective Actuator, Mehti Koklu

Mechanical & Aerospace Engineering Theses & Dissertations

Synthetic jets have previously been studied as actuators for external macroflow control and recently been proposed for internal microflow applications. Despite the wide variety of the potential applications of synthetic jet actuators, the majority of the studies have been done at macro scales. Furthermore, there has not been any design methodology that addresses the effectiveness of the micro synthetic jet actuators. Bearing these needs in mind, a micro synthetic jet configuration is considered in a microscale environment where Kn number is less than 0.1 and more than 0.001. Flowfields are simulated by solving the compressible Navier-Stokes equations. The wall boundary …

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Assessment Of Preliminary Design Approaches For Metallic Stiffened Cylindrical Shell Instability Problems, Vicki Owen Britt Apr 2007

Assessment Of Preliminary Design Approaches For Metallic Stiffened Cylindrical Shell Instability Problems, Vicki Owen Britt

Mechanical & Aerospace Engineering Theses & Dissertations

A preliminary design tool for metallic stiffened fuselage cylindrical panels subjected to longitudinal compression has been developed and validated by comparison to test results. Several methodologies for stiffened panel buckling and failure predictions were examined and evaluated. An appropriate level of analysis fidelity was determined for different failure modes and design details. Results from panel tests conducted to verify analytical methods used to design the Gulfstream V aircraft were presented. The panels were representative of four general skin/stringer configurations on the aircraft. Finite Element analyses and standard analytical methods were used to predict panel failure loads. The accuracy of the …

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Biolaunch, James Cutler Mar 2007

Biolaunch, James Cutler

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by James Cutler titled "BioLaunch" from March 23, 2007.

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Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers Mar 2007

Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers

Theses and Dissertations

This research modeled low-speed flow past idealized engine nacelle clutter in support of aircraft re suppression research. The idealized clutter was comprised of three vertical rows of staggered circular cylinders approximating typical nacelle obstructions such as fuel lines and wire bundles. Single-phase, Detached-Eddy Simulations (DES) were conducted using the commercial CFD solver, Fluent™, to resolve the flow-field dynamics inside the clutter element and determine mechanisms accounting for the failure of suppressant spray droplets from traversing the array under low-speed, free-stream conditions (ReD = 1, 575). The numerical models provided no evidence that span-wise vorticity or non-uniform shedding was responsible for …

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Comparison Of Thermodynamic Equilibrium And Non-Equilibrium Representation Of Materials, Michael J. Vanderhyde Mar 2007

Comparison Of Thermodynamic Equilibrium And Non-Equilibrium Representation Of Materials, Michael J. Vanderhyde

Theses and Dissertations

Hydrocodes are valuable tools in the modeling of shock wave propagation through solids due to high speed impact phenomena. CTH is a hydrocode built with the ability to use multiple EOSs, including the semi-emperical Mie-Gruneisen EOS and tabular Sesame EOS. Modeling high speed impacts necessitates modeling the non-equilibrium thermodynamic states caused by these impacts. A discussion of the non-equilibrium thermodynamics that may be applied to the region directly behind a shock wave is presented, including details of recent attempts to model non-equilibrium impact phenomena in solids. Also, in order to better determine the applicability of the Mie-Gruneisen EOS anbd the …

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Fuel Estimation Using Dynamic Response, Michael S. Hines Mar 2007

Fuel Estimation Using Dynamic Response, Michael S. Hines

Theses and Dissertations

New regulations governing satellites in geostationary orbit require satellites to transfer into a parking orbit as part of the decommissioning process. These regulations increase the demand for accurate fuel estimation techniques for satellites. This study estimates the change in fuel mass from the dynamic response of the Air Force Institute of Technology's simulated satellite (SimSAT) to known control inputs. With an iterative process, the moment of inertia of SimSAT about the yaw axis was estimated by matching a model of SimSAT to the measured angular rates. A change in fuel mass was then estimated from the known relation between the …

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Satellite Attitude Control Using Atmopheric Drag, David B. Guettler Mar 2007

Satellite Attitude Control Using Atmopheric Drag, David B. Guettler

Theses and Dissertations

Attitude control is a requirement for most satellites. Many schemes have been devised over the years including control moment gyros, reaction wheels, spin stabilization and gravity gradient stabilization. For low Earth orbits, the Earth's atmosphere can have an affect on a satellite's orbit and attitude. This research effort examines the feasibility of using the atmosphere to actively control a spacecraft's attitude using drag panels. Using the atmosphere to control spacecraft attitude has been researched in the past however very little research has been done using an active feedback control system to maintain spacecraft attitude. A linear computer model was created …

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Development Of An Experimental Platform For Testing Autonomous Uav Guidance And Control Algorithms, Justin R. Rufa Mar 2007

Development Of An Experimental Platform For Testing Autonomous Uav Guidance And Control Algorithms, Justin R. Rufa

Theses and Dissertations

With the United States' push towards using unmanned aerial vehicles (UAVs) for more military missions, wide area search theory is being researched to determine the viability of multiple vehicle autonomous searches over the battle area. Previous work includes theoretical development of detection and attack probabilities while taking into account known enemy presence within the search environment. Simulations have been able to transform these theories into code to predict the UAV performance against known numbers of true and false targets. The next step to transitioning these autonomous search algorithms to an operational environment is the experimental testing of these theories through …

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Wide Area Search And Engagement Simulation Validation, Michael J. Marlin Mar 2007

Wide Area Search And Engagement Simulation Validation, Michael J. Marlin

Theses and Dissertations

As unmanned aerial vehicles (UAVs) increase in capability, the ability to refuel them in the air is becoming more critical. Aerial refueling will extend the range, shorten the response times, and extend loiter time of UAVs. Executing aerial refueling autonomously will reduce the command and control, logistics, and training efforts associated with fielding UAV systems. Currently, the Air Force Research Lab is researching the various technologies required to conduct automated aerial refueling (AAR). One of the required technologies is the ability to autonomously rendezvous with the tanker. The goal of this research is to determine the control required to fly …

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Active Control Of A Thin Deformable In-Plane Actuated Mirror, Thomas P. Gabriele Jr. Mar 2007

Active Control Of A Thin Deformable In-Plane Actuated Mirror, Thomas P. Gabriele Jr.

Theses and Dissertations

The constitutive relations traditionally used for finding shear stress and heat flux in a fluid become invalid in non-equilibrium flow. Their derivation from kinetic theory only demonstrates they are valid only for small deviations from equilibrium. Because it is fundamentally linked to non-equilibrium, entropy generation is used to investigate the limits of the continuum constitutive relations. However, the continuum equations are inherently limited to near equilibrium conditions due to the constitutive relations; thus kinetic theory must be used as a basis for comparison. Direct Simulation Monte Carlo (DSMC), a particle method alternative to continuum methods, is based on kinetic theory …

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Investigation Into Nanocomposites For Applications In Lightning Strike Protection, Matthew S. Bond, James A. Rodriguez, Hieut T. Nguyen Mar 2007

Investigation Into Nanocomposites For Applications In Lightning Strike Protection, Matthew S. Bond, James A. Rodriguez, Hieut T. Nguyen

Theses and Dissertations

The United States Air Force is continually researching ways to reduce costs associated with aircraft maintenance and improve operational safety. This study focuses on creating a systems engineering process to develop an Integrated Structural Health Monitoring System (ISHMS). The overarching process was then applied to design a conceptual ISHMS for a real-world scenario involving the F-15. Sensor selection, integration and testing were explored in detail using frequency response methods to detect structural damage. Testing was accomplished using a simplified structural specimen with Monitoring & Evaluation Technology Integration System (METIS) disk nodes attached at various locations. Two different METIS disk operation …

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Autonomous Unmarked Aerial Rendezvous For Automated Aerial Refueling (Aar), Brian S. Burns Mar 2007

Autonomous Unmarked Aerial Rendezvous For Automated Aerial Refueling (Aar), Brian S. Burns

Theses and Dissertations

As unmanned aerial vehicles (UAVs) increase in capability, the ability to refuel them in the air is becoming more critical. Aerial refueling will extend the range, shorten the response times, and extend loiter time of UAVs. Executing aerial refueling autonomously will reduce the command and control, logistics, and training efforts associated with fielding UAV systems. Currently, the Air Force Research Lab is researching the various technologies required to conduct automated aerial refueling (AAR). One of the required technologies is the ability to autonomously rendezvous with the tanker. The goal of this research is to determine the control required to fly …

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Optimal Wind Corrected Flight Path Planning For Autonomous Micro Air Vehicles, Michael D. Zollars Mar 2007

Optimal Wind Corrected Flight Path Planning For Autonomous Micro Air Vehicles, Michael D. Zollars

Theses and Dissertations

This research effort focuses on determining the optimal flight path required to put a micro air vehicle's (MAVs) fixed sensor on a target in the presence of a constant wind. Autonomous flight is quickly becoming the future of air power and over the past several years, the size and weight of autonomous vehicles has decreased dramatically. As these vehicles were implemented into the field, it was quickly discovered that their flight paths are severely altered by wind. However, since the size of the vehicle does not allow for a gimbaled camera, only a slight perturbation to the attitude of the …

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Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha Mar 2007

Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha

Theses and Dissertations

Filtered Rayleigh Scattering (FRS) is a non-intrusive technique for studying flowfields. Molecular scattering provides the signal to the camera, and the difference in molecular cross section can be used to discriminate between unmixed gaseous components. The focus of this research is to document the behavior of a horizontal buoyant jet using FRS. A helium jet of precisely controlled mass flow rate is injected into a standard room temperature environment, and FRS provides the means to measure its core trajectory and mixing rate. Trajectory analysis, conducted with consideration of the Reynolds number and Grashof number, can be used to compare these …

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Comparative Analysis Of A High Bypass Turbofan Using A Pulsed Detonation Combustor, Ionio Q. Andrus Mar 2007

Comparative Analysis Of A High Bypass Turbofan Using A Pulsed Detonation Combustor, Ionio Q. Andrus

Theses and Dissertations

It has been proposed that the implementation of a pulsed detonation combustor in a high-bypass turbofan engine would result in an engine that is both more efficient and more reliable. The validity of the performance claims are evaluated based on a comparison between the baseline and hybrid turbofans. The hybrid pulsed detonation engine was modeled in the Numerical Propulsion Simulation System (NPSS) and shares a common architecture with the baseline turbofan model, except that the combustor of the baseline engine is replaced with a pulsed detonation combustor. Detonation effects are calculated using a closed form solution of the Chapman-Jouguet Mach …

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Tension-Compression Fatigue Behavior Of A Carbon Fiber/Epoxy (Im7/Epon 862) Composite Fabricated Using Vacuum Assisted Resin Transfer Molding Process, David W. Katwyk Mar 2007

Tension-Compression Fatigue Behavior Of A Carbon Fiber/Epoxy (Im7/Epon 862) Composite Fabricated Using Vacuum Assisted Resin Transfer Molding Process, David W. Katwyk

Theses and Dissertations

New composite materials and processing methods are continually being developed for use in high performance aerospace systems. One of these new processing methods is the vacuum assisted resin transfer molding (VARTM) process, which shows promise in producing large structural components that have good properties at a lower cost than traditional manufacturing methods. Future widespread use of components manufactured using the VARTM process depends on understanding how these components perform under service conditions, specifically under impact and fatigue conditions. The tension-compression fatigue behavior of a four-harness satin weave carbon fiber/epoxy (IM7/EPON 862) composite manufactured using the VARTM process is investigated in …

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Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner Mar 2007

Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner

Theses and Dissertations

When conducting a space proximity operation, developing high-fidelity estimates of the dynamical and physical properties of a Resident Space Object (RSO) based on post-rendezvous observational data acquired, is imperative for the understanding of the RSO itself and the operating environment. This research investigates the estimation of relative motion dynamics, rotational dynamics, and the feasibility of estimating the moments of inertia of a RSO. Using the Hill-Clohessy-Wiltshire equations, rigid-body dynamics, and estimation theory, a nonlinear least squares estimation algorithm is implemented in the processing of range data from tracked observation points on the RSO body. Through simulation, it was determined that …

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An Evaluation Of High Velocity Wear, Gregory J. Cameron Mar 2007

An Evaluation Of High Velocity Wear, Gregory J. Cameron

Theses and Dissertations

The Holloman High Speed Test Track (HHSTT) is a rocket-powered sled track facility used for testing a variety of hypervelocity aerospace applications. The current speed record is 6,453 miles per hour. While this seems fast there are customers at the track that have requirements demanding even faster speeds. Significant research has been conducted in the area of rail gouging as it relates to the test track, and efforts are under way to reduce and even eliminate this phenomenon. Any steps taken in this effort may eliminate catastrophic sled failures caused by gouging, however wear is another damaging issue that needs …

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Damage Detection Using Lamb Waves For Structural Health Monitoring, Jeffrey S. Crider Ii Mar 2007

Damage Detection Using Lamb Waves For Structural Health Monitoring, Jeffrey S. Crider Ii

Theses and Dissertations

Nondestructive structural health monitoring (SHM) is an evolving technology being developed for monitoring air and space systems. The information gathered on a system's structural integrity through SHM detection methods may result in reduced costly maintenance inspections, enhanced safety, and system failure predictions. This study evaluates Lamb wave approaches used to detect simulated cracks in laboratory experiments on thin plates to detect more realistic damage in a test article representing the complex geometry of an existing aircraft bulkhead. We take a "hot-spot" monitoring approach, where we monitor an area of the structure known to fail. In our experiment, we evaluated the …

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Quick-Turn Finite Element Analysis For Plug-And Play Satellite Structures, Jeffrey E. Naff Mar 2007

Quick-Turn Finite Element Analysis For Plug-And Play Satellite Structures, Jeffrey E. Naff

Theses and Dissertations

Plug-and-play (PnP) satellite construction is a key component of the US Air Force Operational Responsive Space (ORS) effort. The goal of ORS is to provide mission specific satellite support by configuring and launching a satellite to a selected orbit within days of the request. One major challenge during the time limited process is to accurately predict the response of the satellite to harmonic loads that occur during launch and satellite operation. Given the time limitations, constructing finite element (FE) models by traditional methods is not currently a viable option for the ORS timeline. By implementing an approach for rapid FE …

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Adhesion-Delamination Mechanics Of A Prestressed Rectangular Film Adhered Onto A Rigid Substrate, Ming Fung Wong, Gang Duan, Kai-Tak Wan Mar 2007

Adhesion-Delamination Mechanics Of A Prestressed Rectangular Film Adhered Onto A Rigid Substrate, Ming Fung Wong, Gang Duan, Kai-Tak Wan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A prestressed rectangular film clamped at both ends delaminates from a rigid punch. based on a thermodynamic energy balance, the delamination mechanics is derived to relate the simultaneous external tensile force applied to the punch, punch displacement, and contact area. Effects of the coupled tensile residual membrane stress and adhesion energy at the punch-film interface are investigated. a "pinch off" (stable shrinking of the contact area to a line) is predicted, contrasting the nonzero "pull-off" radius in a clamped circular film. the model is useful in understanding the behavior of various adhesion-delamination phenomena, especially in one dimensional capacitive microelectromechanical systems …

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Effects Of Temperature And Environment On Creep Behavior Of An Oxide-Oxide Ceramic Matrix Composite, Jason C. Braun Mar 2007

Effects Of Temperature And Environment On Creep Behavior Of An Oxide-Oxide Ceramic Matrix Composite, Jason C. Braun

Theses and Dissertations

This research investigated the creep behavior of an N720/Al203 composite. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers (NextelTM 720). This ceramic matrix composite (CMC) has no fiber coating and relies on the porous matrix for flaw tolerance. The tensile stress-strain behavior was investigated and the tensile properties measured in the 800-1100 °C temperature range. Tensile creep behavior was examined at 1000 and 1100 °C in laboratory air and in steam environment. In air creep stress was 150 MPa. In steam creep stresses ranged from 100 to 160 MPa. Primary …

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Experimental Investigation Of Turbojet Thrust Augmentation Using An Ejector, David A. Hoffman Mar 2007

Experimental Investigation Of Turbojet Thrust Augmentation Using An Ejector, David A. Hoffman

Theses and Dissertations

The use of computer simulation in the development of autonomously controlled unmanned combat aerial vehicles (UCAV) for wide area search and engagement applications is addressed. Computer simulation is an essential tool to analyze control algorithms designed to optimally employ multiple UCAVs in wide area search and engagement. To be representative of real world mission conditions a simulation must be able to accurately duplicate the performance of the automatic target recognition (ATR) methods that will be used to discriminate between targets and non-targets in actual combat. The objective of this research is to demonstrate a method to validate a simulation's ATR …

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Satellite Formation Control Using Atmospheric Drag, Blake B. Hajovsky Mar 2007

Satellite Formation Control Using Atmospheric Drag, Blake B. Hajovsky

Theses and Dissertations

This study investigates the use of a linear quadratic terminal controller to reconfigure satellite formations using atmospheric drag actuated control while minimizing the loss of energy of the formation. The linearized Clohessy-Wiltshire equations of motion are used to describe the motion of the two-satellite formation about an empty reference position maintained at the formation center. Reconfigurations to final in-plane and elliptical formations are simulated at orbital radii of 6800 km and 7000 km, and the altitude loss and a ?v budget were recorded as performance measures for each reconfiguration. The final states of the spacecraft upon reconfiguration were propagated forward …

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Biolaunch: Ssdl Astrobiology Initiative High-Altitude Balloons And Nanosatellites, Stanford University, Space And Systems Development Laboratory Mar 2007

Biolaunch: Ssdl Astrobiology Initiative High-Altitude Balloons And Nanosatellites, Stanford University, Space And Systems Development Laboratory

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by the Stanford University, Space and Systems Development Laboratory  titled "BioLaunch: SSDL Astrobiology Initiative High-Altitude Balloons and NanoSatellites" from March 13, 2007.

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Biolaunch: Ssdl/Astrobiology Initiative High-Altitude Balloons And Picosatellites, Stanford University, Space And Systems Development Laboratory Mar 2007

Biolaunch: Ssdl/Astrobiology Initiative High-Altitude Balloons And Picosatellites, Stanford University, Space And Systems Development Laboratory

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by the Stanford University, Space and Systems Development Laboratory titled "BioLaunch: SSDL/Astrobiology Initiative High-Altitude Balloons and PicoSatellites" from March 13, 2007.

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Modeling Acoustic Effects On Shear Coaxial Jet Flow Utilizing Molecular Dynamic Simulation, Jermaine S. Sailsman Mar 2007

Modeling Acoustic Effects On Shear Coaxial Jet Flow Utilizing Molecular Dynamic Simulation, Jermaine S. Sailsman

Theses and Dissertations

The purpose of this research is to determine if acoustical effects on a coaxial shear injection jet flow can be modeled through the use of molecular dynamic simulation. Molecular dynamic simulations model flows as a group of interacting particles. The flow in this research was simulated using nitrogen molecules. The initial task involved achieving effective geometry for a simulated coaxial jet. The coaxial jet geometry was driven by the desire for simulations to operate in the continuum regime, which requires very low Knudsen numbers. Three outer to inner jet ratios of 0.0, 1.0, and 6.0 were examined with the inner …

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Design, Construction, And Validation Of The Afit Small Scale Combustion Facility And Section Model Of The Ultra-Compact Combustor, Wesley S. Anderson Mar 2007

Design, Construction, And Validation Of The Afit Small Scale Combustion Facility And Section Model Of The Ultra-Compact Combustor, Wesley S. Anderson

Theses and Dissertations

The AFIT small-scale combustion facility is complete and its first experiment designed and built. Beginning with the partially built facility, detailed designs have been developed to complete the laboratory in order to run small-scale combustion experiments at atmospheric pressure. A sectional model of the Ultra-Compact Combustor has also been designed and built. Although the lab's specific design intent was to study the UCC's cavity-vane interaction, facility flexibility has also been maintained for future work. The design enabled the completion of liquid fuel and air delivery systems, power and control systems, and test equipment. The design includes failsafe operation, remote control, …

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An Analysis Of Aircraft Handling Quality Data Obtained From Boundary Avoidance Tracking Flight Test Techniques, Jason D. Dotter Mar 2007

An Analysis Of Aircraft Handling Quality Data Obtained From Boundary Avoidance Tracking Flight Test Techniques, Jason D. Dotter

Theses and Dissertations

Cooper-Harper ratings (CHRs) have been used to describe and compare aircraft handling qualities for over 40 years, but are by their very nature, subjective. The subjective and sometimes ambiguous results obtained from qualitative handling quality ratings are inconsistent with the rest of the flight test process, where quantifiable results followed by statistical analysis are the norm. This thesis presents a method for obtaining accurate and consistent flight test data that quantifies the handling qualities of a specific aircraft. The method is demonstrated using both pilot-in-the-loop simulations and flight tests with the NF-16D Variable-Stability In-Flight Simulator Test Aircraft (VISTA). Boundary Avoidance …

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Optimal Orbital Coverage Of Theater Operations And Targets, Kimberly A. Sugrue Mar 2007

Optimal Orbital Coverage Of Theater Operations And Targets, Kimberly A. Sugrue

Theses and Dissertations

The use of satellites as a tactical asset to support theater operations is a desired capability for future space operations. Unlike traditional satellite systems designed to provide coverage over the entire globe or large regions, tactical satellites would provide coverage over a small region which can be modeled as a single ground point defined by a latitude and longitude. In order to provide sufficient utility as a theater asset, a satellite should be placed in an orbit that provides a maximum amount of coverage of the target ground point. This study examined the optimization of orbit parameters to maximize the …

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