Engineering Commons^™

United States Air Force Posture Statement 2008, U.S. Air Force

United States Air Force: Publications

The United States Air Force provides the Nation with a powerful deterrent force in times of peace, and it sets the conditions for Joint and Coalition victory in times of war. For over seventeen years, since Operation DESERT SHIELD, the United States Air Force has been engaged in continuous combat operations. Our Airmen have maintained constant watch, deployed continuously, engaged America’s adversaries directly, responded to human crises around the world, and provided the Global Vigilance, Global Reach, and Global Power to secure our Nation.

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 …

A New Method Of Synthesizing Black Birnessite Nanoparticles: From Brown To Black Birnessite With Nanostructures, Marcos A. Cheney, Pradip K. Bhowmik, Shizhi Qian, Sang W. Joo, Wensheng Hou, Joseph M. Okoh

Mechanical & Aerospace Engineering Faculty Publications

A new method for preparing black birnessite nanoparticles is introduced. The initial synthesis process resembles the classical McKenzie method of preparing brown birnessite except for slower cooling and closing the system from the ambient air. Subsequent process, including wet-aging at 7° C for 48 hours, overnight freezing, and lyophilization, is shown to convert the brown birnessite into black birnessite with complex nanomorphology with folded sheets and spirals. Characterization of the product is performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N(2) adsorption ( BET) techniques. Wet-aging and lyophilization times are …

The Effect Of Stirring On The Morphology Of Birnessite Nanoparticles, Marcos A. Cheney, Pradip K. Bhowmik, Shingo Moriuchi, Mario Villabos, Shizhi Qian, Sang W. Joo

Mechanical & Aerospace Engineering Faculty Publications

The effect of mechanical stirring on the morphology of hexagonal layer- structure birnessite nanoparticles produced from decomposition of KMnO₄ in dilute aqueous H₂SO₄ is investigated, with characterization by X- ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high- resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N₂ adsorption (BET). Mechanical stirring during an initial stage of synthesis is shown to produce black birnessite containing nanofibers, whereas granular particulates of brown birnessite are produced without stirring. This is the first reduction synthesis of black birnessite nanoparticles with dendritic morphology without any use …

Multiplexed Predictive Control Of A Large Commercial Turbofan Engine, Hanz Richter, Anil V. Singaraju, Jonathan S. Litt

Mechanical Engineering Faculty Publications

Model predictive control is a strategy well-suited to handle the highly complex, nonlinear, uncertain, and constrained dynamics involved in aircraft engine control problems. However, it has thus far been infeasible to implement model predictive control in engine control applications, because of the combination of model complexity and the time allotted for the control update calculation. In this paper, a multiplexed implementation is proposed that dramatically reduces the computational burden of the quadratic programming optimization that must be solved online as part of the model-predictive-control algorithm. Actuator updates are calculated sequentially and cyclically in a multiplexed implementation, as opposed to the …

Visualizing The Flow Induced By An Air Curtain Over A Mannequin Using Stereo Particle Image Velocimetry, John Edward Fernandes

Mechanical and Aerospace Engineering Theses - Archive

Air curtains find widespread applications in today's world, such as in malls, supermarkets, airports, cold storage, etc., to allow easy pedestrian movement between two different environments. There is interest in understanding the flow induced by traffic through the air curtain in terms of energy efficiency and the ability to provide isolation from contaminants and airborne pathogens. To develop an understanding of the flow, an initial exploratory study was performed using a static mannequin. A stereo particle image velocimetry (SPIV) system was set up to map the flow of the air curtain, installed on top of the doorway, over a mannequin. …

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.

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 …

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 …

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 …

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 …

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 …

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) …

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 …

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 …

On The Near Field Mean Flow Structure Of Transverse Jets Issuing Into A Supersonic Freestream, Dean Anthony Dickmann

Mechanical and Aerospace Engineering Dissertations - Archive

The near field mean flow structure of transverse jets issuing from a surface into supersonic crossflow is examined using numerical methods and separation topology. The Navier-Stokes solver Falcon, developed at Lockheed Martin, was used to simulate the interaction between the jet and freestream over a flat plate and a generic missile body. The near field flow structure included a l bow shock upstream of the jet interacting with the approaching boundary layer that forms a pair of horseshoe vortices while another l- structure closer to the jet formed a second pair of horseshoe vortices. As the jet was turned downstream …

Methodologies For Automated Microassembly, Mohammad A. Mayyas

Mechanical and Aerospace Engineering Dissertations - Archive

The development of micromachining technologies has provided wide applications in micro sensing and actuation. However, most of the demonstrated devices are selectively constructed by fabrication processes that are limited to complexity, configuration, dimension, and material variation. The monolithic fabrication has limitations and does not allow the inclusion of multiple components of incompatible processes. Therefore, the construction of 3D microstructures by heterogeneous microassembly is an alternate manufacturing route. In deterministic, monitored or controlled microassembly there has been considerable research in developing, analyzing and applying distributed algorithms for sensor and sensorless based assembly processes. Meso-scale teleoperated work-cells supported by Nano manipulators have …

Thermal Enhancement Of Stacked Dice Replacing Wire Bonds With Through Silicon Vias At Location Of Die Pads, Venkata Chepuri Krishna Teja

Mechanical and Aerospace Engineering Theses - Archive

Through Silicon vias can offer quick time to market of circuits designed in a modular manner and can also be used to customize the product according to the needs of the customers. This gives a way to avoid both excess inventory risks and larger footprints. A through silicon via could be described as, a vertical component through which a backside interconnect for a pair of bonded wafers forming a wafer stack is ultimately cut into a number of stacked dice. Various embodiments have been patented [1, 2] but implementation of these architectures can be inhibited based on thermal, mechanical and …

Numerical Simulation Of Magnetohydrodynamics, Takahiro Sonoda

Mechanical and Aerospace Engineering Theses - Archive

Use of electromagnetic fields has been shown to be an effective way to control the behavior of electrically conducting fluids. Specifically, the modification of the boundary layer profile with electromagnetic fields can yield performance improvements such as reduced drag and improved heat transfer. Though this approach has been demonstrated computationally and experimentally with conducting liquids (i.e. seawater), application to aerodynamic devices operating in air has not seen the same success. Through the use of numerical simulation and eventually optimization, we hope to develop efficient designs that are effective for boundary layer control for low temperature conducting gases (non-thermal plasmas). The …

An Experimental Study On Thermal Bonding Effects Of Pmma Based Micro-Devices Using Hot Embossing, Varun Sood

Mechanical and Aerospace Engineering Theses - Archive

Basic configuration and functioning of various subsystems of a developed HEMM system for thermal bonding are discussed. The bond strength and micro channel geometry degradations dependence on controlled process parameters in thermal bonding using hot embossing has been investigated. The process parameters examined were bonding temperature, bonding or applied load and holding time. Polymeric substrates with different feature dimensions and thickness were embossed and bonded using hot embossing technology. The feature dimensions before and after bonding were examined to assess the geometry changes as functions of the bonding process. This assessment could provide guidance during the design phase of micro-fluidic …

Derivation Of The Dynamics Equations For Receiver Aircraft In Aerial Refueling, Jayme Lynn Waishek

Mechanical and Aerospace Engineering Theses - Archive

This thesis describes the derivation of a new set of nonlinear, 6--DOF equations of motion of a receiver aircraft undergoing an aerial refueling, including the effect of time-varying mass and inertia properties associated with the fuel transfer and the tanker's vortex induced wind effect. Since the center of mass of the receiver is time--varying during the fuel transfer, the equations are written in a reference frame that is geometrically fixed in the aircraft. Due to the fact that aerial refueling simulation and control deal with the position and orientation of the receiver relative to the tanker, the equations of motion …

A Cfd Investigation Of Axisymmetric Microthruster Nozzles For Use On Nano-Satellites, Michael R. O'Gara

Master's Theses - Daytona Beach

The performance of microthruster nozzles (^ 0.1 N thrust) depending on nozzle contour, propellant and surroundings, destined for use in nanosatellite missions, is investigated via a numerical approach using the Wind-US flow solver. An experimental apparatus designed to measure microthruster performance in atmospheric or vacuum conditions used to aid numerical simulations is also presented. Comparing the numerical and experimental results show an approximate 25% drop in efficiency for unknown reasons. An evaluation of favorable nozzle contours suggested by previous researchers is conducted, and the results demonstrate the need for a more rigorous treatment of the nozzle flow at the exit …

Stress Distribution And Strength Prediction Of Composite Laminates With Multiple Holes, Brian Esp

Mechanical and Aerospace Engineering Dissertations - Archive

The major purpose of this study was to investigate failure of composite laminates with multiple unloaded holes in close proximity. The least square boundary collocation method for anisotropic materials was utilized to determine the state of stress. The approach utilized collocation on both the internal and external boundaries, making it relatively easy to implement. The method compared favorably to both published and finite element solutions. A failure prediction approach for an infinite, symmetric and balanced laminate, with two holes in close proximity was presented. The baseline material for consideration was IM7/977-3, a carbon fiber/epoxy lamina. The failure prediction method was …

An Analytical And Numerical Model For Design Of Non- Uniformly Powered Silicon Chips Based On Both Thermal And Device Clock Performance, Abhihit D. Kaisare

Mechanical and Aerospace Engineering Dissertations - Archive

Silicon chips continue to grow in capabilities, complexity and performance. Silicon chips typically integrate functional components such as logic and level two (L2) cache memory in their architecture. This functional integration of logic and memory results in improved performance of the chip. However, the integration also introduces a layer of complexity in the thermal design and management of silicon chips. As a direct result of functional integration, the power map on a silicon chip is typically highly non-uniform and the assumption of a uniform heat flux across the chip surface has been shown to be invalid post Pentium II architecture. …

Thermal Stresses Of Composite Beams With Rectangular And Tubular Cross-Sections, Chia-Wei Su

Mechanical and Aerospace Engineering Theses - Archive

Closed-form analytical solutions for laminated composite beams with tubular and rectangular cross-sections are developed for evaluating the thermal induced stresses. The derivations are based on modified lamination theory and parallel axis theorem. The present approach includes variation of ply stiffness along the contour of the cross-section. The interlaminar shear stress of cantilever composite beam with rectangular cross-section under a transverse load is analytically proved to be independent of temperature change in uniform temperature environment. Three-dimensional finite element models for computing thermal stresses of both cross-sections are developed using commercial software package ANSYS 10. The results obtained from analytical solutions give …

A Computational Method For Flow Separation Detection And Control For Axial Compressor Airfoils, Chang Jun Meang

Master's Theses - Daytona Beach

Conducting full annulus experiments on multistage compressors is costly and time consuming due to the complexity of the experimental processes. To reduce complexity, Computational Fluid Dynamics (CFD) methods are applied to turbomachinery and other applications in recent analysis of such cases. CFD methods are widely used within the aerospace industry and are increasingly demonstrating their reliability. For axial compressors, it is known that highly staggered compressor stators will increase the aerodynamic loading on the stator, which directly relates to the compressor stall and efficiency. In this work, compressor stators stagger angle is increased 4 ° to induce separation on the …