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Articles 1 - 22 of 22
Full-Text Articles in Engineering
Simulation And Analysis Of Wing Rock Physics For A Generic Fighter Model With Three Degrees-Of-Freedom, Ahmed Saad
Simulation And Analysis Of Wing Rock Physics For A Generic Fighter Model With Three Degrees-Of-Freedom, Ahmed Saad
Theses and Dissertations
Modern fighter designs have been associated with lateral self-excited oscillations own as "Wing Rock". Simulations of wing rock by flow visualization utilities have been encouraged to develop a complete understanding of the fluid mechanism that drives the motion as well as for prediction purposes. Previous wind/water tunnel simulations have been limited to a single degree-of freedom (DoF) in roll. In this study, for the first time, wing rock is computationally simulated in three DoF: roll, sideslip, and vertical motion to study the effect of adding file sideslip and vertical motion. The results are for a generic fighter model consisting of …
Three-Dimensional Dynamic Stress Analysis Of Sandwich Panels, Victor Y. Perel
Three-Dimensional Dynamic Stress Analysis Of Sandwich Panels, Victor Y. Perel
Theses and Dissertations
A layerwise geometrically nonlinear theory for a thick sandwich plate was developed by introducing assumptions on a variation of transverse strains in the thickness direction of the faces and the core of the plate. An effect of transverse extensibility or compressibility of the core and the face sheets is taken into account, and the terms associated with transverse shear strain of the face sheets and the core are included into the expression for the strain energy. Displacements, obtained by integration of the strain-displacement relations, depend nonlinearly on a coordinate in the thickness direction, and are continuous at the boundaries between …
Finite Element Model Updating Using Antiresonant Frequencies, Keith W. Jones
Finite Element Model Updating Using Antiresonant Frequencies, Keith W. Jones
Theses and Dissertations
The applications of antiresonant frequencies to finite element (FE) model updating are few and usually limited to numerical examples. This work uses antiresonant frequencies in the model updating of an experimental structure and analyzes the physical correctness of the updated model by using it to detect damage. Antiresonant frequencies were used in the FE model updating of a six-meter aluminum truss. The model used rigid links to model welded and bolted joints. Rigid link dimensions were used as parameters in an iterative update based on eigenvalue and antiresonance sensitivities. The first update used 11 natural frequencies and 21 antiresonant frequencies …
Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland
Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland
Theses and Dissertations
This thesis investigated the properties of a steam injector to see if the concept might be suitable for use on a liquid rocket engine. A steam injector is a device developed in the 1850's to inject feedwater into the boiler on a steam locomotive without any moving parts. The injectors uses a small portion of the steam generated in the boiler to increase the pressure of the feedwater to a level high than the pressure in the boiler. Previous experiments claim that condensation of steam to water was necessary for an injector to work. This experiment tested injection without condensation …
Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel
Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel
Theses and Dissertations
This thesis evaluates an oxide/oxide ceramic matrix composite, N720/A, for high temperature aerospace applications. The composite consists of a porous alumina matrix reinforced by ten plies of Nextel 720 fibers in a balanced 8 harness satin weave. Monotonic tensile and fatigue tests were performed at room temperature and 1200 °C. The effect of moisture on 1200 °C fatigue life was also examined. Modulus, maximum and minimum strain, and stress-strain hysteresis were monitored to characterized fatigue damage. Retained strength of all specimens that survived 100000 fatigue cycles was tested. Microscopy and fractography were used to examine damage and fracture surfaces. N720/A …
Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper
Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper
Theses and Dissertations
High cycle fatigue is an important consideration in blade design for turbomachinery. Blades in an engine undergo countless loading cycles in a lifetime, the result of pressure waves that propagate upstream and downstream from disturbances in the flow. Better understanding of these effects would allow blade designers to reduce the effects of high cycle fatigue, such as costly recurring maintenance or catastrophic engine failure. An experimental study was undertaken to determine the unsteady flow field upstream of a single cylinder in a subsonic flow. Von Karman vortex shedding from the cylinder produced a forcing function much like periodic blade passage …
Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh
Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh
Theses and Dissertations
The Department of Defense has identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance its reliability and lifetime, and reduce payload structural mass. DoD space programs stand to benefit significantly from advances in vibration isolation technology. This study explores potential hybrid vibration isolation using active and adaptive control with a passive vibration isolator. The active control methods are Proportional-Integral-Derivative (PID) control and a skyhook damper. Lyapunov analysis is used to develop the structural adaptive control scheme. Simulink and Matlab simulations investigate these control methodologies on a lumped mass dynamic …
Navigation Of Satellite Clusters, Jeffrey S. Davis
Navigation Of Satellite Clusters, Jeffrey S. Davis
Theses and Dissertations
The relative position determination of a cluster of satellites in near circular orbit was investigated in previous thesis work. The purpose of this thesis is to extend the concept to cover absolute position determination. A Bayes filter is used for the estimator with dynamics based on the two-body problem extended to account for J2 perturbations. Measurements consist of combining Global Positioning System (GPS) data for each satellite and range data between the satellites. Simulations were conducted investigating the accuracy obtainable when combining the measurements for input into the filter. Performance results consist of comparing the magnitude of the time error …
Attitude Control And Multimedia Representation Of Air Force Institute Of Technology’S (Afit’S) Simulation Satellite (Simsat), Joseph M. Fulton
Attitude Control And Multimedia Representation Of Air Force Institute Of Technology’S (Afit’S) Simulation Satellite (Simsat), Joseph M. Fulton
Theses and Dissertations
This document describes the systematic construction of the AFIT-sponsored program to develop a laboratory-based satellite simulator. The simulation satellite (SIMSAT) system will provide a useful tool for resident staff while teaching attitude control concepts. A brief overview of attitude control theory is provided as well as a discussion of the benefits of multimedia use in education. A detailed discussion of the satellite's components allows the reader to become familiar with each piece of SIMSAT. Software control models are provided as well as a multimedia lesson plan on satellite attitude control. Also included in this document are potential experimental uses in …
Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer
Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer
Theses and Dissertations
The general Mission Route Planning (MRP) Problem is the process of selecting an aircraft flight path in order to fly from a starting point through defended terrain to target(s), and return to a safe destination. MRP is a three-dimensional, multi-criteria path search. Planning of aircraft routes involves an elaborate search through numerous possibilities, which can severely task the resources of the system being used to compute the routes. Operational systems can take up to a day to arrive at a solution due to the combinatorial nature of the problem, which is not acceptable, because time is critical in aviation. Also, …
Modeling Piezoceramic Twist Actuation In Single-Cell Anisotropic Torque Box Of Low-Observable Uav Wing, Peter Cseke Jr.
Modeling Piezoceramic Twist Actuation In Single-Cell Anisotropic Torque Box Of Low-Observable Uav Wing, Peter Cseke Jr.
Theses and Dissertations
The reduction of an aircraft's radar cross section can increase its survivability in hostile airspace by making it more difficult to locate and track by enemy radar. Replacing articulated flight control surfaces with adaptive controls will reduce surface discontinuities, and enhance low observability. Actuation of the aerodynamic surfaces is achieved by an electric field applied to PZT actuators embedded in the top and bottom skins, creating differential strain and shear in the host substrate. This creates torsion about the elastic axis, and a change in the wing lift coefficient. The torsion of the designed baseline UAV's wing torquebox was modeled …
An Experimental Investigation On Periodic Forced Vibrations Of A Bladed Disk, Colin J. Duffield
An Experimental Investigation On Periodic Forced Vibrations Of A Bladed Disk, Colin J. Duffield
Theses and Dissertations
Aircraft engine blades are subject to harmonic forcing produced from periodic wakes created by fixed stators. Prolong or repeated exposure at blade resonant frequencies can cause vibration-induced fatigue, otherwise known as High Cycle Fatigue (HCF). Structural mistuning coupled with HCF causes premature blade failures, excessive operational costs and increased engine servicing. This study offered a novel approach to characterize mistuning effects on bladed disk forced vibration behavior. A model fan reduced in dynamic scale from an operational jet engine fan and with weak inter-blade coupling was fabricated. Aerodynamic disturbances produced by the stators were replicated by magnets attached to a …
Integrating Automated Multi-Disciplinary Optimization In Preliminary Design Of Non-Traditional Aircraft, Mehmet Fidanci, Jeffrey R. Miller, Douglas J. Strauss
Integrating Automated Multi-Disciplinary Optimization In Preliminary Design Of Non-Traditional Aircraft, Mehmet Fidanci, Jeffrey R. Miller, Douglas J. Strauss
Theses and Dissertations
Current methods of aircraft conceptual design lack the ability to quickly generate detailed analysis, particularly of nontraditional designs such as blended wing body craft. This study developed a method to resolve this problem by creating a flexible, parametrically driven conceptual model in an object-oriented, adaptive modeling environment from which analysis and optimization may rapidly be performed. These object-oriented techniques are incorporated into a traditional conceptual design process. All objects inherit dependency-tracking and demand-driven calculations. Design Analysis was performed within the modeling language and utilized interfaces to other software packages. A detailed mesh, suitable for input into finite element analysis programs, …
Damage Identification In A Real Structure Using Resonant And Anti-Resonant Frequencies, Douglas E. Gaeta
Damage Identification In A Real Structure Using Resonant And Anti-Resonant Frequencies, Douglas E. Gaeta
Theses and Dissertations
There exists a need to remotely monitor the structural integrity of large space structures without costly manned missions. This work focused on further damage detection characterization of the Air Force Institute of Technology's Flexible Truss Experiment (FTE). The FTE is intended to be representative of a large space structure. Several damage detection algorithms were developed and tested for the FTE using 112 different damage conditions and the one undamaged condition. The algorithms were trained using two frequency response functions (FRFs) from each damage case and then tested using the same two FRFs, but from newly acquired data. A data reduction …
A Comparative Analysis Of Cockpit Display Development Tools, Matthew J. Gebhardt
A Comparative Analysis Of Cockpit Display Development Tools, Matthew J. Gebhardt
Theses and Dissertations
Currently, no standard methodology exists that enables cockpit display engineers to evaluate software tools used in the development of graphical cockpit displays. Furthermore, little research has been accomplished in comparing current software development tools with traditional hand-coded methods, This research effort discusses a framework for analyzing cockpit display software development tools and follows through with a detailed analysis comparing today's hand-coding standard, OpenGL, with two of today's cockpit display software development suites, Virtual Application Prototyping System (VAPS) and Display Editor. The comparison exploits the analysis framework establishing the advantages and disadvantages of the three software development suites. The analysis framework …
Three Dimensional Formation Flight Control, James K. Hall
Three Dimensional Formation Flight Control, James K. Hall
Theses and Dissertations
Automating the control of an aircraft flying in formation necessitates the extension of the theory of formation flight control to allow for three dimensional maneuvers. The formation was modeled as a two-aircraft, leader and wingspan, formation. Both aircraft has its own three dimensional, rotating and translating, Cartesian axes system, with special attention being given to the motion of the leader in relation to the wingspan. The controller operated using the equations of motion expressed in the rotating reference frame of the wing aircraft. The control system has seven states, three inputs and three disturbance signals to model the dynamics of …
Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak
Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak
Theses and Dissertations
This study describes how lean principles and thinking can be applied to space range operations. The "lean" concepts of the right thing, right place, and the right time are applicable and relevant to this study. The basis for the lean concepts and principles considered is the Lean Aerospace Initiative (LAI). The LAI originated from the International Motor Vehicle Program (IMVP) that was conducted by a team from the Massachusetts Institute of Technology (MIT). The LAI is a collaborative research program involving government, industry, labor, and academia (primarily MIT). The partnership began in 1993 through support of the U.S. Air Force …
Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard
Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard
Theses and Dissertations
Many common operational situations in High Altitude Endurance (HAE) UAV reconnaissance necessitate more direct human involvement in the aircraft control process than is currently acknowledged or allowed. The In-Flight Replanning System (IFRS) is developed as a notional solution, with the Global Hawk HAE UAV as the reconnaissance system model. Problematic scenarios for current in-flight mission replanning systems are presented and revisited with the IFRS, demonstrating improved replanning results.
Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher
Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher
Theses and Dissertations
A computational study was conducted on the use of aft-mounted fairings for passive drag reduction on a sphere at Re=866,000. The sphere dimensions and operating Reynolds number were selected to approximate the flow around a proposed aircraft laser turret for which experimental data was available. To establish the validity of the computational model, flow predictions were compared to sphere data available in the open literature. The model, exercised in both the laminar and turbulent modes, showed good agreement with the published data. Two proposed laser turret fairings were then evaluated computationally: a large fairing (beginning at 49.5 degrees past the …
Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg
Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg
Theses and Dissertations
The Air Force is interested in the research of supercritical jet and rocket fuels, as well as the effects of thermally induced fuel degradation. As future flight vehicles travel at ever increasing Mach numbers, greater heat loads will be imposed upon the fuel. The primary purpose of this study is to develop a computational model for predicting fuel decomposition and bulk fuel temperatures in a stimulated heated flow reactor. The System for Thermal Diagnostic Studies (STDS), located in the Air Force Research Laboratory's Fuels Branch, is used to analyze fuels under supercritical temperatures and pressures. Computational simulations of the STDS …
Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling
Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling
Theses and Dissertations
This research investigated control loop time delay and its effect on UAV handling qualities. Compensation techniques to improve handling qualities in the presence of varying amounts of time delay were developed and analyzed. One technique was selected and successfully flight-tested on a UAV. Flight-testing occurred at a constant flight condition with varying levels of additional time delay introduced into the control loop. Research pilots performed a pitch tracking task and gave Cooper-Harper ratings and comments. Tracking errors were used as a quantitative measure of Pilot/Display/UAV system performance. Predictive pitch compensation was found to significantly reduce pilot workload and improve Cooper-Harper …
Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner
Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner
Theses and Dissertations
Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. The USAF Scientific Advisory Board (SAB) identified "Large lightweight structures for optics and antennas" as a revolutionary primary technology to be developed for the Air Force of the 21st Century. A membrane primary mirror in a space-based imaging system has the ability to overcome current payload constraints and meet evolutionary needs of the future. The challenge of membrane optics in space is the process of implementing adaptive optics technology …