Engineering Commons^™

Life-Extending Control For A Highly Maneuverable Flight Vehicle, Si-Bok Yu

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation investigates the feasibility and potential of life extension control logic for reducing fatigue within aerospace vehicle structural components. A key underpinning of this control logic is to exploit nonintuitive, optimal loading conditions which minimize nonlinear crack growth behavior, as predicted by analytical fatigue models with experimentally validated behavior. A major simplification in the development of life extension control logic is the observation and justification that optimal stress loading conditions, as described by overload magnitude ratio and application interval, are primarily independent of crack length and therefore, component age. This weak relationship between optimal stress loading and structural age …

New Approaches To Gortler And Tollmien-Schlichting Boundary-Layer Instabilities, Vijay Kalburgi

Mechanical & Aerospace Engineering Theses & Dissertations

A detailed understanding of the physical processes that lead to instability and transition in the external viscous boundary layers of airfoils has been the goal of researchers for decades. This study seeks to enhance our understanding of Gortler and Tollmien-Schlichting instabilities through a critical review of prior theoretical methodology and fundamental experiments, the development of dimensionally consistent disturbance equations, and novel interpretation of the resulting flow physics revealed by their solutions to explain the process of transition.

Gortler vortices arise in boundary layers along concave surfaces due to centrifugal effects and these vortices in combination with other instabilities play an …

Nonlinear H Infinity Missile Longitudinal Autopilot Design With Θ-D Method, Ming Xin, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In this paper, a new nonlinear control synthesis technique, the theta- D method, is employed to design a missile longitudinal autopilot. The θ-D technique yields suboptimal solutions to nonlinear optimal control problems in the sense that it provides approximate solution to the Hamilton-Jacobi-Bellman (HJB) equation. Semi-global asymptotic stability can be achieved by manipulating the perturbation terms which are added to the cost function in developing a series solution. Furthermore, this method can be used to provide an approximate closed-form solution to the state dependent Riccati equation. The particular θ-D methodology adopted in this paper is referred to as θ-D H …

Stanford Classes At Nasa Ames, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Stanford Classes At NASA Ames" from December 10, 2002.

Torque Limit Of A Mechanical Fastener In A Graphite/Epoxy Joint, Kristian M. Kostreva

Master's Theses - Daytona Beach

Presently there is a lack of confidence amongst engineers when specifying the preload of a mechanical fastener in a composite joint due to a lack of a fundamental knowledge base regarding the behavior of composites under fastener compressive load. As such, a novel experimental procedure was developed herein to determine the through-the-thickness compressive (TTTC) material properties. A total of 206 property tests were performed on four different graphite/epoxy material systems. The results confirmed that TTTC material properties vary with fiber orientation, laminate thickness, fiber volume fraction, and even laminate surface finish. Hence, the 'rule of mixtures' provides a poor estimate …

Use Of Dimples To Suppress Boundary Layer Separation On A Low Pressure Turbine Blade, Kurt P. Rouser

Theses and Dissertations

Flow separation on a low pressure turbine blade is explored at Reynolds numbers of 25k, 45k and 100k. Experimental data is collected in a low-speed, draw-down wind tunnel using a cascade of eight Pak-B blades. Flow is examined from measurements of blade surface pressures, boundary layer parameters, exit velocities, and total pressure losses across the blade. Two recessed dimple shapes are assessed for suppressing flow separation and associated losses. One dimple is spherical, and the second is asymmetric, formed from a full dimple spanwise half-filled. A single row of each dimple shape is tested at 50%, 55% and 65% axial …

Stanford Student Satellite Program, Robert J. Twiggs, Bulent Altan

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Bulent Altan titled "Stanford Student Satellite Program" from December 20, 2002.

Implementation Of Gy-Eq For Deterministic Effects Limitation In Shield Design, John W. Wilson, Myung-Hee Y. Kim, Giovanni De Angelis, Francis A. Cucinotta, Nobuaki Yoshizawa, Francis F. Badavi

Mathematics & Statistics Faculty Publications

The NCRP has recently defined RBE values and a new quantity (Gy-Eq) for use in estimation of deterministic effects in space shielding and operations. The NCRP's RBE for neutrons is left ambiguous and not fully defined. In the present report we will suggest a complete definition of neutron RBE consistent with the NCRP recommendations and evaluate attenuation properties of deterministic effects (Gy-Eq) in comparison with other dosimetric quantities.

Using The Boundary Element Method For Prediction Of Sound Radiated From An Arbitrarily Shaped Vibrating Body, Mark J. Christensen

Masters Theses

The Boundary Element Method can be used to predict sound pressure levels radiated from an arbitrarily shaped vibrating body. Using the Direct, Indirect and Approximation formulation one can solve such an ‘exterior’ acoustic problem. In this work, the Direct formulation was chosen. The two major methods employed for implementation of this formulation are the Combined Helmholtz Integral Equation Formulation (CHIEF) and the Burton–Miller Method. Since the CHIEF method was easier to program and adapt to changes, it was decided that the CHIEF method would be the focus of this research. Using the CHIEF method as a guide, a computer simulation …

Lunar Lava Tube Radiation Safety Analysis, Giovanni De Angelis, J. W. Wilson, M. S. Clowdsley, J. E. Nealy, D. H. Humes, J. M. Clem

Mathematics & Statistics Faculty Publications

For many years it has been suggested that lava tubes on the Moon could provide an ideal location for a manned lunar base, by providing shelter from various natural hazards, such as cosmic radiation, meteorites, micrometeoroids, and impact crater ejecta, and also providing a natural environmental control, with a nearly constant temperature, unlike that of the lunar surface showing extreme variation in its diurnal cycle. An analysis of radiation safety issues on lunar lava tubes has been performed by considering radiation from galactic cosmic rays (GCR) and Solar Particle Events (SPE) interacting with the lunar surface, modeled as a regolith …

Emerald Final Report For Nag5-9737, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Emerald Final Report for NAG5-9737" from November 22, 2002.

Electromagnetic Scattering From A Gap In A Magneto-Dielectric Coating On An Infinite Ground Plane, George R. Simpson

Theses and Dissertations

The electromagnetic scattering from a gap in a magneto-dielectric coating on an infinite ground plane is analyzed. In this context, the gap forms a break only in the magneto-dielectric slab coating while the ground plane is continuous and unbroken. Volume equivalence is used to convert the gap region to one containing unknown volumetric equivalent electric and magnetic currents. The equivalent problem then is one of these currents radiating in the presence of an unbroken grounded magneto-dielectric slab. A Green's function for this geometry is developed consisting of two terms: a direct coupling term and correction term to account for the …

The Aeronautics Education, Research, And Industry Alliance (Aerial) 2002 Report, Brent D. Bowen, Mary M. Fink, Jocelyn S. Nickerson, Uno Aviation Institute

Faculty Books and Monographs

UNOAI Report 02-7

The NASA Nebraska Space Grant Consortium (NSGC) & EPSCoR programs at the University I of Nebraska at Omaha are involved in a variety of innovative research activities. Such research is supported through the Aeronautics Education, Research, and Industry Alliance (AERIAL) and collaborative seed funds. AERIAL is a comprehensive, mulch-faceted, five year NASA EPSCoR initiative that contributes substantially to the strategic research and technology priorities of NASA while intensifying Nebraska’s rapidly growing aeronautics research and development endeavors.

AERIAL includes three major collaborative research teams (CRTs) whose nexus is a common focus in aeronautics research. Each CRT - Small …

The Family Science Starter Kit: A Manual To Assist You In The Development Of A Family Aeronautical Science Program, Henry R. Leher, Uno Aviation Institute

Faculty Books and Monographs

UNOAI Report 02-6

This book is designed to involve families working together on several different hands-on activities during evening meetings at school. The basis for these activities is the in-school study of related science and mathematical concepts and topics by the students in each family. The program provides an opportunity for families to work together in an interesting and enjoyable manner. The Family Aeronautical Science demonstration project consisted of three parts: (1) the in-school study of aeronautics during select science classes; (2) the extensive after-school use of the school’s computer laboratory; and (3) evening Family Aeronautical Science Nights. Key parts …

Cubesat Workshop: Frascati, Italy, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "CubeSat Workshop Frascati, Italy" from October 26, 2002.

The Next Generation Of Innovative Space Engineers: University Students Are Now Getting A Taste Of Space Experience Building, Launching And Operating Their Own Space Experiments With Low-Cost Picosatellites, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

An article authored by Professor Bob Twiggs titled "The Next Generation of Innovative Space Engineers: University Students are Now Getting a Taste of  Space Experience Building, Launching and Operating their own Space Experiments with Low-Cost Picosatellites" from October 22, 2002.

The Next Generation Of Innovative Space Engineers: University Students Are Now Getting A Taste Of Space Experience Building, Launching And Operating Their Own Space Experiments With Low-Cost Picosatellites, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "The Next Generation of Innovative Space Engineers: University Students are Now Getting a Taste of Space Experience Building, Launching and Operating their own Space Experiments with Low-Cost Picosatellites" and presented at the 5th International ESA Conference on Guidance Navigation & Control on October 22, 2002.

Photoreflectance Spectroscopy Of Strained (In)Gaasn/Gaas Multiple Quantum Wells, J. B. Heroux, Xiaodong Yang, W. I. Wang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The effect of a variation of the indium and nitrogen concentrations in Inᵪ Ga_1-x As_1-y N_y /GaAs multiquantum wells grown by molecular beam epitaxy is studied systematically by room temperature photoreflectance spectroscopy. The band gap redshift caused by a nitrogen fraction of 1.5% decreases by as much as 30% as the indium fraction increases from 0% to 20%. A moderate increase of electron effective mass (Δmₑ ~ 0.03m₀) is found in all samples containing nitrogen (y ≳ 1%). In compressively strained quantum wells, the energy separation between the first confined heavy and light hole energy levels decreases …

Iridium: Space Engineering - Project Based Learning By Working Real Space Programs, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Iridium: Space Engineering - Project Based Learning by Working Real Space Programs" from October 15, 2002.

Cubesat 2002 Cdr, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "CubeSat 2002 CDR" from October 14, 2002.

Modeling Of Acoustic Emission Failure Mechanism Data From A Unidirectional Fiberglass/Epoxy Tensile Test Specimen, Daniel R. Lendzioszek

Master's Theses - Daytona Beach

The purpose of this work was to model the acoustic emission (AE) flaw growth data that resulted from the tensile test of a unidirectional fiberglass/epoxy specimen. The data collected and stored during the test were the six standard AE quantification parameters for each event. A classification neural network was used to sort the data into five failure mechanism clusters. The resulting frequency histograms of the sorted data were then mathematically modeled herein using the three types of Johnson distributions: bounded, lognormal, and unbounded. These provided a reasonably good fit for all six AE parameter distributions for each of the five …

An Intelligent System For Monitoring The Microgravity Environment Quality On-Board The International Space Station, Paul P. Lin, Kenol Jules

Mechanical Engineering Faculty Publications

An intelligent system for monitoring the microgravity environment quality on-board the International Space Station is presented. The monitoring system uses a new approach combining Kohonen's self-organizing feature map, learning vector quantization, and a back propagation neural network to recognize and classify the known and unknown patterns. Finally, fuzzy logic is used to assess the level of confidence associated with each vibrating source activation detected by the system.

Darpa, Robert J. Twiggs, Jordi Puig-Suari, Brian Horias

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professors Bob Twiggs, Jordi Puig-Suari, and Brian Horais titled "DARPA" from September 18, 2002.

A Cubesat Derived Design For A Unique Commericial Science Application, Matthew R. Long, Eric Tapio, Glenn Tran, Greg Rodgers, Allen Lorenz, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

An article authored by Matthew R. Long, Eric Tapio, Glenn Tran, Greg Rodgers, Allen Lorenz, and Robert Twiggs titled "A CubeSat Derived Design for a Unique Commericial Science Application" from September 5, 2002.

Adaptive Harmonic Balance Method For Unsteady, Nonlinear, One-Dimensional Periodic Flows, Raymond C. Maple

Theses and Dissertations

A new adaptive split-domain harmonic balance computational fluid dynamics (CFD) method is developed to solve highly nonlinear time-periodic flows such as those found in turbomachinery. The basic harmonic balance CFD method transforms an unsteady time-periodic problem into a steady-state problem by assuming a solution in the form of a Fourier series in time. The new method employs a unique multi-domain split-operator solution technique to remove a large-series stability restriction present in previous harmonic balance CFD approaches. In addition, the new method adapts the frequency content to the flow, starting with a small number of Fourier frequencies and augmenting the frequency …

Mean Performance Optimization Of An Orbiting Distributed Aperture By Warped Aperture Image Plane Comparisons, Timothy W. Parker

Theses and Dissertations

This work models the aggregate performance of satellite receiver formations functioning as orbiting interferometers as compared to filled apertures of similar geometries. These models facilitate selecting initial conditions for formations such that their control-free dynamics yield interferometry performance with minimal errors as compared to the filled apertures. The solution method draws on the dynamic models of an orbiting planar satellite formation to define the size and shape of a reference aperture and to define the degrees of freedom for the formation members. The paths of formation elements yield geometries for which the aggregate performance of the array of discrete receivers …

Analysis For Cooperative Behavior Effectiveness Of Autonomous Wide Area Search Munitions, Sang M. Park

Theses and Dissertations

The purpose of this study is to investigate how a simulation model can accurately represent the performance of the autonomous wide area search munitions, and to find the effectiveness of the cooperative behavior on the autonomous munitions. Though it does not provide a practical solution for the development of the autonomous wide area search munitions, this research will show some meaningful allocations of the munitions tasks that are applicable to the development of the autonomous munitions. For the first phase, this thesis presents how accurately a simplified simulation model can represent a proposed weapon system by comparing the simulation results …

Spacecraft Design Program, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Spacecraft Design Program" from August 6, 2002.

Opal, Sapphire, And The Fgn, James Cutler

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by James Cutler titled "Opal, Sapphire, and the FGN" on August 6, 2002.

Responsive Access, Small Cargo, Affordable Launch: Introduction Briefing, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Preston H. Carter II titled "Responsive Access, Small Cargo, Affordable Launch: Introduction Briefing" from August 6, 2002.