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5,776 full-text articles. Page 193 of 198.

Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love 2010 Air Force Institute of Technology

Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love

Theses and Dissertations

Particle image velocimetry (PIV) has been carried out using solid carbon dioxide (CO2) particles as the seed material to continue the development of clean seeding for use in large-scale, closed-circuit tunnels. Testing occurred in two wind tunnels at subsonic and supersonic speeds using dry ice particles generated by allowing liquefied CO2 to expand from a small diameter injector tube through a larger diameter shroud tube. The particles were injected into the plenum and discrete solid particles, suitable for PIV measurements, were present in the test section. Data on particle size were first collected using a Malvern particle size ...


Consideration Of Wear Rates At High Velocities, Stephen P. Meador 2010 Air Force Institute of Technology

Consideration Of Wear Rates At High Velocities, Stephen P. Meador

Theses and Dissertations

The goal of this research is to study sliding contact wear of test sled slippers at high velocities. Experimentation representative of the slippers is infeasible, so numerical studies are used. An Eulerian-Lagrangian hydrocode called CTH is used to study mechanical wear. Failure criteria have been established to evaluate the stresses and strains resulting from the hydrocode simulation of a single asperity collision. The results from the hydrocode simulations are scaled to account for slipper bounce and multiple asperities, and these results produce total wear values that are approximately 90% of total experimental wear. Slipper thermodynamics have also been evaluated. The ...


Consideration Of Wear Rates At High Velocity, Chad S. Hale 2010 Air Force Institute of Technology

Consideration Of Wear Rates At High Velocity, Chad S. Hale

Theses and Dissertations

The development of the research presented here is one in which high velocity relative sliding motion between two bodies in contact has been considered. The experimental results of a VascoMax 300 maraging steel slipper sliding on an AISI 1080 steel rail during a January 2008 sled test mission were considered for the determination of high velocity wear rates. The numerical model, based on a metallographic study of a test slipper, contained all of the physical features present in order to adequately characterize high velocity wear rates. Two-dimensional, plane strain models have been implemented in the explicit finite element code, ABAQUS ...


Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett 2010 Air Force Institute of Technology

Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett

Theses and Dissertations

This research sought to validate a proof of concept regarding shape memory alloy actuation of a flapping-wing blimp. Specimen wires were subjected to cyclic voltage at increasing frequencies to quantify expected strains. A laser vibrometer captured 2048 sample velocities during single contraction and elongation cycles, and the resulting samples were used to calculate displacements. Displacements were determined ten times for each specimen and frequency to compute averages. Subsequently, a circumventing frame was designed to encase a blimp envelope and provide support for a flapping motion actuation system. Contraction of shape memory wire translated force to the flapping mechanism via bellcranks ...


Effectsof Prior Aging At 260 °C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 260 °C: Experiment And Modeling, Bradley K. Diedrick 2010 Air Force Institute of Technology

Effectsof Prior Aging At 260 °C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 260 °C: Experiment And Modeling, Bradley K. Diedrick

Theses and Dissertations

The purpose of this research was to investigate the inelastic deformation behavior of PMR-15 neat resin, a high-temperature polymer, at 260 °C. The experimental program was designed to explore the influence of strain rate on loading and unloading behaviors. In addition, the effect of prior strain rate on creep, relaxation, and recovery responses was evaluated. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading. Early failures occur before fully establishing inelastic flow. The creep, relaxation, and recovery responses are significantly influenced by prior strain rate. The experimental results suggest the behavior of PMR-15 at 260 °C can be ...


Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston 2010 Air Force Institute of Technology

Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston

Theses and Dissertations

This study was focused on obtaining accurate experimental data for the validation of the geometrically exact beam theory from a series of experiments in which high quality surface shape and deflection data was collected. Many previous experiments have experienced issues with data collection or test articles which the researchers were unable to overcome. The test program was performed in two stages: qualification and joined-wing. The qualification stage validated the experimental procedures on simple 72 in long aluminum beams with 8 in x 0.5 in cross-sections. The joined-wing stage was the primary experiment focused on obtaining quality data for use ...


Validation Of A Novel Approach To Solving Multibody Systems Using Hamilton's Weak Principle, Ashton D. Hainge 2010 Air Force Institute of Technology

Validation Of A Novel Approach To Solving Multibody Systems Using Hamilton's Weak Principle, Ashton D. Hainge

Theses and Dissertations

A novel approach for formulating and solving for the dynamic response of multibody systems has been developed using Hamilton’s Law of Varying Action as its unifying principle. In order to assure that the associated computer program is sufficiently robust when applied across a wide range of dynamic systems, the program must be verified and validated. The purpose of the research was to perform the verification and validation of the program. Results from the program were compared with closed-form and numerical solutions of simple systems, such as a simple pendulum and a rotating pendulum. The accuracy of the program for ...


Analysis Of Slewing And Attitude Determination Requirements For Ctex, William J. Starr Jr. 2010 Air Force Institute of Technology

Analysis Of Slewing And Attitude Determination Requirements For Ctex, William J. Starr Jr.

Theses and Dissertations

This thesis examines the slewing and attitude determination requirements for the Chromotomographic Experiment (CTEX), a chromotomographic-based hyperspectral imager, to be mounted on-board the Japanese Experiment Module (JEM) External Facility (EF). The in-track slewing requirement is driven by the facts that CTEx has a very small field of view (FOV) and is required to collect 10 seconds of data for any given collection window. The need to slew in the cross-track direction is a product of the small FOV and target/calibration site access. CTEx incorporates a two-axis slow-steering dwell mirror with a range of +/- 8 degrees and an accuracy of ...


Artificial Inhomogeneous Tapered Impedance Sheet Characterization And Applications, Jeffrey P. Massman 2010 Air Force Institute of Technology

Artificial Inhomogeneous Tapered Impedance Sheet Characterization And Applications, Jeffrey P. Massman

Theses and Dissertations

The ability to manipulate a complex impedance sheet about a PEC or general dielectric cylinder of arbitrary diameter to control the overall scattering characteristics at particular angles for shielding or scattering applications is presented. It is shown that with the capability to readily control both the real and imaginary components of a percolated lossy film's effective impedance, specific impedance distributions can be obtained to effectively direct the overall nulls in the bistatic scattering pattern. The exact approach only requires negligible truncation error of the matrix solution and can be applied to cylinders of arbitrary size. This approach relies on ...


Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal 2010 Air Force Institute of Technology

Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal

Theses and Dissertations

Current government and industry standards in spacecraft testing result in an Assembly, Integration, and Test (AIT) timeline greater than six months. These standards will not support the vision of Operationally Responsive Space (ORS) to deploy a satellite within six days to fill an urgent need. Using the Air Force Research Laboratory’s Plug-and-Play Satellite (PnPSat), multiple Rapid AIT trials were conducted. By exercising the AIT process with various spacecraft configurations and personnel, methods for reducing or modifying traditional testing regimen were investigated.


Smore Phase 2: An Upgrade In Valve Systems & Startup Procedure For A Small Methanol Oxygen Liquid Rocket Engine, Christian Soria 2010 California Polytechnic State University - San Luis Obispo

Smore Phase 2: An Upgrade In Valve Systems & Startup Procedure For A Small Methanol Oxygen Liquid Rocket Engine, Christian Soria

Aerospace Engineering

A Methanol-Oxygen liquid rocket engine was designed and manufactured under the California Polytechnic State University Aerospace Department by students in a graduate level rocket propulsion class. The SMORE, previously known as the KORE, is now in an ongoing testing and developing stage with plans to incorporate it into the aerospace undergraduate propulsion lab. Phase 2 of the liquid rocket engine development is to produce a start-up procedure that will improve the safety due to manual operation and poor ignition conditions. A propane ignition system along with the implementation of electrically operated solenoid valves to control the fuels and oxidizer were ...


Quantifying Seismic Risk For Portable Ground Support Equipment At Vandenberg Air Force Base, Joshua Brian Lowe 2010 California Polytechnic State University - San Luis Obispo

Quantifying Seismic Risk For Portable Ground Support Equipment At Vandenberg Air Force Base, Joshua Brian Lowe

Master's Theses and Project Reports

This project develops a quantitative method to evaluate the seismic risk for portable GSE at Vandenberg Air Force Base. Using the latest probability data available from the USGS, risk thresholds are defined for portable GSE having the potential to cause a catastrophic event. Additionally, an example tool for design engineers was developed from the seismic codes showing the tipping hazard case can be simplified into strict geometrical terms. The misinterpretation and confusion regarding the Range Safety 24 Hour Rule exemption can be avoided by assessing seismic risk for portable GSE. By using the methods herein to quantify and understand seismic ...


Modeling Disk Cracks In Rotors By Utilizing Speed Dependent Eccentricity, Andrew L. Gyekenyesi, Jerzy T. Sawicki, Wayne C. Haase 2010 Ohio Aerospace Institute

Modeling Disk Cracks In Rotors By Utilizing Speed Dependent Eccentricity, Andrew L. Gyekenyesi, Jerzy T. Sawicki, Wayne C. Haase

Mechanical Engineering Faculty Publications

This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and ...


Autonomous Satellite Operations For Cubesat Satellites, Jason Lionel Anderson 2010 California Polytechnic State University - San Luis Obispo

Autonomous Satellite Operations For Cubesat Satellites, Jason Lionel Anderson

Master's Theses and Project Reports

In the world of educational satellites, student teams manually conduct operations daily, sending commands and collecting downlinked data. Educational satellites typically travel in a Low Earth Orbit allowing line of sight communication for approximately thirty minutes each day. This is manageable for student teams as the required manpower is minimal. The international Global Educational Network for Satellite Operations (GENSO), however, promises satellite contact upwards of sixteen hours per day by connecting earth stations all over the world through the Internet. This dramatic increase in satellite communication time is unreasonable for student teams to conduct manual operations and alternatives must be ...


System Integration And Attitude Control Of A Low-Cost Spacecraft Attitude Dynamics Simulator, Ryan L. Kinnett 2010 California Polytechnic State University – San Luis Obispo

System Integration And Attitude Control Of A Low-Cost Spacecraft Attitude Dynamics Simulator, Ryan L. Kinnett

Master's Theses and Project Reports

The CalPoly Spacecraft Attitude Dynamics Simulator mimics the rotational dynamics of a spacecraft in orbit and acts as a testbed for spacecraft attitude control system development and demonstration. Prior to this thesis, the simulator platform and several subsystems had been designed and manufactured, but the total simulator system was not yet capable of closed-loop attitude control. Previous attempts to make the system controllable were primarily mired by data transport performance. Rather than exporting data to an external command computer, the strategy implemented in this thesis relies on a compact computer onboard the simulator platform to handle both attitude control processing ...


Combined H∞-Feedback Control And Iterative Learning Control Design With Application To Nanopositioning Systems, Brian E. Helfrich, Chibum Lee, Douglas A. Bristow, Jingyan Dong, Srinivasa M. Salapaka, Placid M. Ferreira, X. H. Xiao, Andrew G. Alleyne 2010 Missouri University of Science and Technology

Combined H∞-Feedback Control And Iterative Learning Control Design With Application To Nanopositioning Systems, Brian E. Helfrich, Chibum Lee, Douglas A. Bristow, Jingyan Dong, Srinivasa M. Salapaka, Placid M. Ferreira, X. H. Xiao, Andrew G. Alleyne

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This paper examines a coordinated feedback and feedforward control design strategy for precision motion control (PMC) systems. It is assumed that the primary exogenous signals are repeated; including disturbances and references. Therefore, an iterative learning control (ILC) feedforward strategy can be used. The introduction of additional non-repeating exogenous signals, including disturbances, noise, and reset errors, necessitates the proper coordination between feedback and feedforward controllers to achieve high performance. A novel ratio of repeated versus non-repeated signal power in the frequency domain is introduced and defined as the repetitive-to-non-repetitive (RNR) ratio. This frequency specific ratio allows for a new approach to ...


Parametric Viscous Analysis Of Gust Interaction With Stationary And Elastically Mounted Airfoil, Timothy M. Hollenshade Jr. 2010 Embry-Riddle Aeronautical University - Daytona Beach

Parametric Viscous Analysis Of Gust Interaction With Stationary And Elastically Mounted Airfoil, Timothy M. Hollenshade Jr.

Theses - Daytona Beach

This thesis details the development and implementation of a module within a high-accuracy numerical viscous analysis code to simulate the nonlinear interaction of SD7003 airfoil with non-uniform, unsteady incoming flow. The study is focused on the low-Re number unsteady flows typical of MAV applications in which a gust encounter can induce a particularly significant aerodynamic and aeroelastic response. Efficient source models are developed to introduce sharp-edge and time-harmonic gust perturbations with specified amplitude, frequency and duration inside the computational domain through the source terms in the governing momentum equations. Parametric analysis of gust-airfoil interactions for different steady airfoil loads is ...


Constrained Kalman Filtering Via Density Function Truncation For Turbofan Engine Health Estimation, Daniel J. Simon, Donald L. Simon 2010 Cleveland State University

Constrained Kalman Filtering Via Density Function Truncation For Turbofan Engine Health Estimation, Daniel J. Simon, Donald L. Simon

Electrical Engineering & Computer Science Faculty Publications

Kalman filters are often used to estimate the state variables of a dynamic system. However, in the application of Kalman filters some known signal information is often either ignored or dealt with heuristically. For instance, state variable constraints (which may be based on physical considerations) are often neglected because they do not fit easily into the structure of the Kalman filter. This article develops an analytic method of incorporating state variable inequality constraints in the Kalman filter. The resultant filter truncates the probability density function (PDF) of the Kalman filter estimate at the known constraints and then computes the constrained ...


Adaptive Control Applied To The Cal Poly Spacecraft Attitude Dynamics Simulator, Matthew C. Downs 2010 California Polytechnic State University - San Luis Obispo

Adaptive Control Applied To The Cal Poly Spacecraft Attitude Dynamics Simulator, Matthew C. Downs

Master's Theses and Project Reports

The goal of this thesis is to use the Cal Poly Spacecraft Attitude Dynamics Simulator to provide proof of concept of two adaptive control theories developed by former Cal Poly students: Nonlinear Direct Model Reference Adaptive Control and Adaptive Output Feedback Control. The Spacecraft Attitude Dynamics Simulator is a student-built air bearing spacecraft simulator controlled by four reaction wheels in a pyramidal arrangement. Tests were performed to determine the effectiveness of the two adaptive control theories under nominal operating conditions, a “plug-and-play” spacecraft scenario, and under simulated actuator damage. Proof of concept of the adaptive control theories applied to attitude ...


Improving Stability Of Stabilized And Multiscale Formulations In Flow Simulations At Small Time Steps, Ming-Chen Hsu, Y. Bazilevs, V. M. Calo, T. E. Tezduyar, T.J.R. Hughes 2010 University of California, San Diego

Improving Stability Of Stabilized And Multiscale Formulations In Flow Simulations At Small Time Steps, Ming-Chen Hsu, Y. Bazilevs, V. M. Calo, T. E. Tezduyar, T.J.R. Hughes

Ming-Chen Hsu

The objective of this paper is to show that use of the element-vector-based definition of stabilization parameters, introduced in [T.E. Tezduyar, Computation of moving boundaries and interfaces and stabilization parameters, Int. J. Numer. Methods Fluids 43 (2003) 555–575; T.E. Tezduyar, Y. Osawa, Finite element stabilization parameters computed from element matrices and vectors, Comput. Methods Appl. Mech. Engrg. 190 (2000) 411–430], circumvents the well-known instability associated with conventional stabilized formulations at small time steps. We describe formulations for linear advection–diffusion and incompressible Navier–Stokes equations and test them on three benchmark problems: advection of an L-shaped ...


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