Aerospace Engineering Commons^™

Characterization Of Thermal Challenges In Electronics : Leakage Current, Co-Architectural Design And Rack Level Cooling, Uthaman Raju

Mechanical and Aerospace Engineering Theses - Archive

Since the advent of transistors and integrated circuits the complexity and functionality of the electronic products has gone up. In line with this, the scaling of the products is catching up at all levels of packaging. Current electronics era is driven by a mantra - "Miniaturization". Recently the number of transistors on high end microprocessor has exceeded a billon mark. The design at board level becomes sophisticated to meet the growing demands. All of these lead to thermal and reliability challenges. A good thermal design is one which makes sure that the chip is operating at its rated frequency or …

Experimental Analysis Of The Hydrogen Sulfide Absortion Phenomena In Brine/Oil Mixtures As A Function Of System Pressure And H2s, Luis Zea

Electronic Theses and Dissertations

In underground oil reservoirs, Hydrogen sulfide is usually found coexisting with the oil due to bacteria reduction over a long period of time. The amount of H2S in the oil varies from place to place around the globe. When the oil extraction process begins, the presence of Hydrogen sulfide becomes noticeable as drilling tools, piping and other equipment suffer from sulfide stress cracking, electrochemical corrosion and corrosion fatigue. For this reason, the oil industry invests millions of dollars per year trying to find better ways to reduce the amount of H2S in oil. An important part of the current investigations …

Rolls Royce Declares Bankruptcy, John Alfred Heitmann

History Faculty Publications

Despite more than sixty years of engineering excellence, Rolls-Royce failed in its attempt to design and manufacture a radically new jet engine to meet contractual obligations with the Lockheed Corp. Consequently, both British and U.S. governments had to step in to avoid an unprecedented economic catastrophe.

Antennas For Portable Communications In The Uwb And Gps Spectra., Giuseppe Ruvio

Doctoral

The thesis describes a study of antennas for solutions in emerging systems. An account of the fundamental principles of these antennas is given together with an outline of the basic electromagnetic theory on which the designs are based. While the main focus is on antennas for Ultra Wideband (UWB) systems, some additional work was carried out on enhancing performance of circularly polarised antennas for satellite navigation systems. The study focussed on the design of highly efficient broadband antennas with particular requirements for size compactness, gain stability, phase-linearity, and the use of low-cost materials. These requirements are particularly important for UWB …

Manufacturing Of Transparent Composites Using Vacuum Infusion Process, Jason Niles Gallagher

Masters Theses

"Glass is the most commonly used transparent material. However, glass is not suitable where low weight and high strength are required. For many applications there exists a need for mechanically strong composite materials of high optical quality and transparency equivalent to window glass. Glass fiber reinforced transparent composite is a viable solution. Transparency is maintained by precisely matching the refractive index of the matrix with that of the glass fiber. Aircraft canopies and transparent armor can be potential applications for this new class of materials.

In the present work, transparent composites are manufactured using vacuum infusion process. Both rectangular glass …

Analysis Of Access-To-Space Missions Utilizing On-Board Energy Management And Entropic Analysis, Tyler Winter

Masters Theses

"The overall objective of this study is the thermodynamically consistent quantification of second-law and performance losses for vehicle configurations implemented or suggested for access-to-space missions and the development of the relationships between the mission entropy generation and overall mission performance. The detailed theory which allows thermodynamically rigorous loss accounting (entropy generation and direct relationship to vehicle performance) is developed and discussed for aerospace vehicles. A full vehicle trajectory code utilizing simplified models for multi-stage rockets and air-breathing propulsion systems is developed and validated specifically for use as a testbed for second law-based theory and concepts. Results are shown in which …

Nonlinear Random Response Of Large-Scale Sparse Finite Element Plate Bending Problems, Swati Chokshi

Civil & Environmental Engineering Theses & Dissertations

Acoustic fatigue is one of the major design considerations for skin panels exposed to high levels of random pressure at subsonic/supersonic/hypersonic speeds. The nonlinear large deflection random response of the single-bay panels aerospace structures subjected to random excitations at various sound pressure levels (SPLs) is investigated. The nonlinear responses of plate analyses are limited to determine the root-mean-square displacement under uniformly distributed pressure random loads. Efficient computational technologies like sparse storage schemes and parallel computation are proposed and incorporated to solve large-scale, nonlinear large deflection random vibration problems for both types of loading cases: (1) synchronized in time and (2) …

Design Of An Adaptive Autopilot For An Expendable Launch Vehicle, Clinton Plaisted

Electronic Theses and Dissertations

This study investigates the use of a Model Reference Adaptive Control (MRAC) direct approach to solve the attitude control problem of an Expendable Launch Vehicle (ELV) during its boost phase of flight. The adaptive autopilot design is based on Lyapunov Stability Theory and provides a useful means for controlling the ELV in the presence of environmental and dynamical uncertainties. Several different basis functions are employed to approximate the nonlinear parametric uncertainties in the system dynamics. The control system is designed so that the desire dresponse to a reference model would be tracked by the closed-loop system. The reference model is …

Towards A Metric For The Assessment Of Safety Critical Control Systems, Oscar R. Gonzalez, Jorge R. Chavez-Fuentes, W. Steven Gray

Electrical & Computer Engineering Faculty Publications

There is a need for better integration of the fault tolerant and the control designs for safety critical systems such as aircraft. The dependability of current designs is assessed primarily with measures of the interconnection of fault tolerant components: the reliability function and the mean time to failure. These measures do not directly take into account the interaction of the fault tolerant components with the dynamics of the aircraft. In this paper, a first step to better integrate these designs is made. It is based on the observation that unstable systems are intrinsically unreliable and that a necessary condition for …

Analytical Solution To The Wave Equation With Discrete Pressure Sources: A Model For The Rijke Tube, Eduardo G. Perez

Graduate Theses, Dissertations, and Problem Reports (ETD)

Despite of having been studied for several decades the phenomena of combustion instabilities are not well understood. Pressure waves due to the combustion instabilities can become violent being detrimental for both the performance and combustor life. A good prediction of the pressure distribution inside the combustor is important in order to prevent theoccurrence of this phenomenon. In this work a technique for solving the wave equation with discrete sources (or sinks) using the Green's functions was developed. One and two-dimensional approaches for cylindrical and Cartesian coordinates withconstant speed of sound were solved. Also the case of one-dimensional axially varying temperature …

A Comparison Of Filtering Approaches For Aircraft Engine Health Estimation, Daniel J. Simon

Electrical and Computer Engineering Faculty Publications

Different approaches for the estimation of the states of linear dynamic systems are commonly used, the most common being the Kalman filter. For nonlinear systems, variants of the Kalman filter are used. Some of these variants include the LKF (linearized Kalman filter), the EKF (extended Kalman filter), and the UKF (unscented Kalman filter). With the LKF and EKF, performance varies depending on how often Jacobians (partial derivative matrices) are updated. In other words, we see a tradeoff between computational effort and filtering performance. With the unscented Kalman filter, Jacobians are not calculated but computational effort is typically high due to …

Attitude Determination Using Imaging Lidar, Camille Decoust

Master's Theses - Daytona Beach

The purpose of this study is to determine the attitude of an out of control object using a new technology called lidar (Light Ranging and Detection). As the number of spacecraft continues to grow, it is paramount to introduce a new type of autonomous on-orbit satellite inspection and repair involving docking. Traditional space vision technology is based on video systems. This method is limited by the necessity of operating when the target is illuminated by the sunlight or using its own source of illumination. The use of laser imaging technology offers an elegant solution to these challenges. This approach allows …

Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara

Mechanical & Aerospace Engineering Theses & Dissertations

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and unsteady solutions are obtained …

Experimental Investigation Of Active Control Of Bluff Body Vortex Shedding, Ilteris Koc

Mechanical & Aerospace Engineering Theses & Dissertations

Mean and fluctuating forces acting on a body are strongly related to vortex shedding generated behind it. Therefore, it is possible to obtain substantial reductions of at least the unsteady forces if vortex shedding is controlled or its regularity is reduced. While conventional active flow control methods are mainly concerned with direct interaction with, and alteration of, the mean flow about a body, modern techniques involve altering existing flow instabilities using relatively small inputs to obtain large-scale changes of mean flows. Aerodynamic flow control may be intended to delay or suppress boundary layer separation through creation of a boundary layer …

How Are Nasa Engineers Motivated? An Analysis Of Factors That Influence Nasa Goddard Engineers’ Level Of Motivation, Howard Eric Kea

Antioch University Dissertations & Theses

NASA is an organization known for pushing the envelope of engineering and scientific achievement. It can be argued that engineers working for NASA are intrinsically highly motivated due to the nature of the work and the mission of NASA. This study explores how supervisor behaviors, both intrinsic and extrinsic and demographic factors influence motivation of NASA Goddard engineers in their current environment. Recent Congressional and Office of Management and Budget (OMB) policies, such as full cost accounting, levy strict oversight of project spending. As a result of these policies, NASA engineers must now focus their attention on getting assigned work …

Seasonal Adaptation Of Vegetation Color In Satellite Images, Srinivas Jakkula, Vamsi K.R. Mantena, Ramu Pedada, Yuzhong Shen, Jiang Li, Hamid R. Arabnia (Ed.)

Electrical & Computer Engineering Faculty Publications

Remote sensing techniques like NDVI (Normal Difference vegetative Index) when applied to phenological variations in aerial images, ascertained the seasonal rise and decline of photosynthetic activity in different seasons, resulting in different color tones of vegetation. The rise and fall of NDVI values decide the biological response, either the green up or brown down [1]. Vegetation in green up period appears with more vegetative vigor and during brown down period it has a dry appearance. This paper proposes a novel method that identifies vegetative patterns in satellite images and then alters vegetation color to simulate seasonal changes based on training …