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Aerospace Engineering Commons™

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2007

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Articles 91 - 120 of 202

Full-Text Articles in Aerospace Engineering

Prediction Of Fatigue Life In 7075-T6 Aluminum From Neural Network Analysis Of Acoustic Emission Data, Nicholas S. Spivey May 2007

Prediction Of Fatigue Life In 7075-T6 Aluminum From Neural Network Analysis Of Acoustic Emission Data, Nicholas S. Spivey

Master's Theses - Daytona Beach

Through the use of an acoustic emission (AE) data acquisition system, a Kohonen self-organizing map, and a back-propagation neural network, AE data from 7075-T6 aluminum specimens were used to classify failure mechanisms and predict the number of fatigue cycles to failure. AE waveforms were captured from 40 notched tensile specimens during the low-cycle fatiguing process. A Kohonen self-organizing map and initial data filters were used to classify the data into two distinct failure mechanisms, plane strain and plane stress fracture, plus a third less prevalent mechanism. These results were employed to construct a back-propagation neural network to predict the number …

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Management Of An Intelligent Argumentation Network For A Web-Based Collaborative Engineering Design Environment, Xiaoqing Frank Liu, Man Zheng, Ganesh K. Venayagamoorthy, Ming-Chuan Leu May 2007

Management Of An Intelligent Argumentation Network For A Web-Based Collaborative Engineering Design Environment, Xiaoqing Frank Liu, Man Zheng, Ganesh K. Venayagamoorthy, Ming-Chuan Leu

Computer Science Faculty Research & Creative Works

Conflict resolution is one of the most challenging tasks in collaborative engineering design. In our previous research, a web-based intelligent collaborative system was developed to address this challenge based on intelligent computational argumentation. However, two important issues were not resolved in that system: priority of participants and self-conflicting arguments. In this paper, we develop two methods for incorporating priorities of participants into the computational argumentation network: 1) weighted summation and 2) re-assessment of strengths of arguments based on priority of owners of the argument using fuzzy logic inference. In addition, we develop a method for detection of self-conflicting arguments. Incorporation …

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Recent Developments In Smart Adaptive Structures For Solar Sailcraft, Mark Whorton, Young Kim, Jerry Oakley, Olawale Adetona, Lee Keel Apr 2007

Recent Developments In Smart Adaptive Structures For Solar Sailcraft, Mark Whorton, Young Kim, Jerry Oakley, Olawale Adetona, Lee Keel

Information Systems and Engineering Management Research Publications

The "Smart Adaptive Structures for Solar Sailcraft" development activity at MSFC has investigated issues associated with understanding how to model and scale the subsystem and multi-body system dynamics of a gossamer solar sailcraft with the objective of designing sailcraft attitude control systems. This research and development activity addressed three key tasks that leveraged existing facilities and core competencies of MSFC to investigate dynamics and control issues of solar sails. Key aspects of this effort included modeling and testing of a 30 m deployable boom; modeling of the multi-body system dynamics of a gossamer sailcraft; investigation of control-structures interaction for gossamer …

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Launch And Field Operations Without Leaving Your Office And Cubesat Test Opportunities, Robert J. Twiggs Apr 2007

Launch And Field Operations Without Leaving Your Office And Cubesat Test Opportunities, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint presentation created by Professor Bob Twiggs titled "Launch and Field Operations without leaving your Office and CubeSat Test Opportunities" from April 19, 2007.

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Coupled-Mode Theory For Stimulated Raman Scattering In High-Q/Vm Silicon Photonic Band Gap Defect Cavity Lasers, Xiaodong Yang, C. W. Wong Apr 2007

Coupled-Mode Theory For Stimulated Raman Scattering In High-Q/Vm Silicon Photonic Band Gap Defect Cavity Lasers, Xiaodong Yang, C. W. Wong

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We examine the dynamics of stimulated Raman scattering in designed high-Q/Vm silicon photonic band gap nanocavities through the coupled-mode theory framework towards optically-pumped silicon lasing. The interplay of other X(3) effects such as two-photon absorption and optical Kerr, related free-carrier dynamics, thermal effects, as well as linear losses such as cavity radiation and linear material absorption are included and investigated numerically. Our results clarify the relative contributions and evolution of the mechanisms, and demonstrate the lasing and shutdown thresholds. Our studies illustrate the conditions for continuous-wave and pulsed highly-efficient Raman frequency conversion for practical realization in monolithic silicon …

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The Onset For Compressibility Effects For Aerofoils In Ground Effect, G. Doig, T.J. Barber, E. Leonardi, A.J. Neely Apr 2007

The Onset For Compressibility Effects For Aerofoils In Ground Effect, G. Doig, T.J. Barber, E. Leonardi, A.J. Neely

Aerospace Engineering

The influence of flow compressibility on a highly-cambered inverted aerofoil in ground effect is presented, based on two-dimensional computational studies. This type of problem has relevance to open-wheel racing cars, where local regions of high-speed subsonic flow form under favourable pressure gradients, even though the maximum freestream Mach number is typically considerably less than Mach 0.3. An important consideration for CFD users in the field is addressed in this paper, the freestream Mach number at which flow compressibility significantly affects aerodynamic performance. More broadly, for aerodynamicists, the consequences of this are also considered. Comparisons between incompressible and compressible CFD siulations …

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Fabrication And Compressive Behavior Of Corrugated Aramid-Epoxy Cellular Solids, Jeffrey Arthur Schneider Apr 2007

Fabrication And Compressive Behavior Of Corrugated Aramid-Epoxy Cellular Solids, Jeffrey Arthur Schneider

Master's Theses - Daytona Beach

Cellular solids are materials whose base material does not always occupy the entire solid fraction available. A number of cellular solids can provide blast protection and absorb impact energy, but few perform well resisting blunt object (ballistic) penetration. In this thesis, a method is proposed for fabricating cellular solids from aramid-epoxy composites that can absorb impact energy and resist blunt object penetration. The aramid-epoxy samples were fabricated using wet-layup techniques, with two different styles of Kevlar 49 woven fabric in a variety of orientations. Test sample density ranged from 0.08 0.23 g/cm3. Different lamination orientations, assembly techniques, and bonding adhesives …

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Investigation Of Magnetic Field Profile Effects In Hall Thrusters, Oren Kornberg Apr 2007

Investigation Of Magnetic Field Profile Effects In Hall Thrusters, Oren Kornberg

Master's Theses - Daytona Beach

The purpose of this study was to show the relationship of different magnetic field profiles to the acceleration region length of a Hall thruster. The general transport equations were simplified and solved using a one-dimensional analysis. Some of the model assumptions include quasineutrality, Maxwellian electrons, and negligible thruster wall effects. The solved equation kept magnetic field as an input to the model for the analysis. The magnetic field was altered by changing the shape through the thruster, while keeping the maximum point fixed, and by shifting the profile, while keeping the shape fixed. Results indicate a strong correlation between the …

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Impact-Induced Damage Characterization Of Composite Plates Using Neural Networks, Steve Eugene Watkins, Farhad Akhavan, Rohit Dua, K. Chandrashekhara, Donald C. Wunsch Apr 2007

Impact-Induced Damage Characterization Of Composite Plates Using Neural Networks, Steve Eugene Watkins, Farhad Akhavan, Rohit Dua, K. Chandrashekhara, Donald C. Wunsch

Electrical and Computer Engineering Faculty Research & Creative Works

Impact-induced damage in fiber-reinforced laminated composite plates is characterized. An instrumented impact tower was used to carry out low-velocity impacts on thirteen clamped glass/epoxy composite plates. A range of impact energies was experimentally investigated by progressively varying impactor masses (holding the impact height constant) and varying impact heights (holding the impactor mass constant). The in-plane strain profiles as measured by polyvinylidene fluoride (PVDF) piezoelectric sensors are shown to indicate damage initiation and to correlate to impact energy. Plate damage included matrix cracking, fiber breakage, and delamination. Electronic shearography validated the existence of the impact damage and demonstrated an actual damage …

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Efficient Sampling For Non-Intrusive Polynomial Chaos Applications With Multiple Uncertain Input Variables, Serhat Hosder, Robert W. Walters, Michael Balch Apr 2007

Efficient Sampling For Non-Intrusive Polynomial Chaos Applications With Multiple Uncertain Input Variables, Serhat Hosder, Robert W. Walters, Michael Balch

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The accuracy and the computational efficiency of a Point-Collocation Non-Intrusive Polynomial Chaos (NIPC) method applied to stochastic problems with multiple uncertain input variables has been investigated. Two stochastic model problems with multiple uniform random variables were studied to determine the effect of different sampling methods (Random, Latin Hypercube, and Hammersley) for the selection of the collocation points. The effect of the number of collocation points on the accuracy of polynomial chaos expansions were also investigated. The results of the stochastic model problems show that all three sampling methods exhibit a similar performance in terms of the the accuracy and the …

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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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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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Development Of An Acoustic Measurement Capability For Automobile Testing In Open-Jet Wind Tunnels, Brianne Y. Williams Apr 2007

Development Of An Acoustic Measurement Capability For Automobile Testing In Open-Jet Wind Tunnels, Brianne Y. Williams

Mechanical & Aerospace Engineering Theses & Dissertations

Automobile aeroacoustics is still in its beginning stages. Understanding where control of the noise sources is addressed using mainly exploratory experimental methods and idealized models. The difficulty of reducing noise levels lies in the mechanisms that generate noise. Sound sources are generated from unsteady aerodynamics which arises from turbulent boundary layers and from regions of separated flow over the vehicle. These regions are subjected to unsteady pressures which are interpreted by the driver as undesirable noise. In order to reduce the noise around an automobile, the individual sources are best identified by . performing full-scale wind tunnel testing. This identification …

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Aerodynamic And Acoustic Investigations Of An Advanced Over-The-Wing Nacelle Transport Aircraft Configuration, Geoffrey A. Hill Apr 2007

Aerodynamic And Acoustic Investigations Of An Advanced Over-The-Wing Nacelle Transport Aircraft Configuration, Geoffrey A. Hill

Mechanical & Aerospace Engineering Theses & Dissertations

The transonic aerodynamic and low-speed acoustic characteristics of an advanced, Over-the-Wing Nacelle (OWN), subsonic transport configuration are assessed. The cruise aerodynamics of the OWN were analyzed using both inviscid Euler and viscous Navier-Stokes CFD. Results of the assessments are compared to a similar configuration with a more traditional Under-the-Wing Nacelle (UWN) installation and a similar reference Wing-Body Qualitative observations and quantitative drag computations are made for the three configurations at a cruise Mach number of0.78, an approximate altitude of35,000-ft, and a CL, of 0.44. It was found that the OWN's novel inboard wing channel design is effective in …

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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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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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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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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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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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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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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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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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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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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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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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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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