Aerospace Engineering Commons^™

A Gap Analysis Of Meteorological Requirements For Commercial Space Operators, Nicholas J. Stapleton

Doctoral Dissertations and Master's Theses

Commercial space companies will soon be the primary method of launching people and supplies into orbit. Among the critical aspects of space launches are the meteorological concerns. Laws and regulations pertaining to meteorological considerations have been created to ensure the safety of the space industry and those living around spaceports; but, are they adequate? Perhaps the commercial space industry can turn to the commercial aviation industry to help answer that question. Throughout its history, the aviation industry has dealt with lessons learned from mishaps due to failures in understanding the significance of weather impacts on operations. Using lessons from the …

Structural Damage Classification Using Support Vector Machines, Xiang Li

Doctoral Dissertations and Master's Theses

In this research, a methodology to classify crack and corrosion metallic damages using a time-frequency representation method and support vector machines is investigated. Piezoelectric ceramic actuators are utilized to generate guided wave signals on a set of aluminum beam coupons with different damage features, such as types, locations, and thicknesses. The short-time Fourier transform is applied to analyze the measured signals. For damage classification, the spectrograms obtained from finite element models are employed to train a two-class support vector machine learning classifier. The classifier is able to correctly classify different types of damages based upon the measured signals collected from …

Neural Network Fatigue Life Prediction In Steel I-Beams Using Mathematically Modeled Acoustic Emission Data, Prathikshen Nambiar Selvadorai

Doctoral Dissertations and Master's Theses

The purpose of this research is to predict fatigue cracking in metal beams using mathematically modeled acoustic emission (AE) data. The AE data was collected from nine samples of steel I-beam that were subjected to three-point bending caused by cyclic loading. The data gathered during these tests were filtered in order to remove long duration hits, multiple hit data, and obvious outliers. Based on the duration, energy, amplitude, and average frequency of the AE hits, the filtered data were classified into the various failure mechanisms of metals using NeuralWorks® Professional II/Plus software based self-organizing map (SOM) neural network. The parameters …

Acoustic Emission Signal Classification For Gearbox Failure Detection, Jun Shishino

Doctoral Dissertations and Master's Theses

The purpose of this research is to develop a methodology and technique to determine the optimal number of clusters in acoustic emission (AE) data obtained from a ground test stand of a rotating H-60 helicopter tail gearbox by using mathematical algorithms and visual inspection. Signs of fatigue crack growth were observed from the AE signals acquired from the result of the optimal number of clusters in a data set. Previous researches have determined the number of clusters by visually inspecting the AE plots from number of iterations. This research is focused on finding the optimal number of clusters in the …

The Effects Of Familiarity And Persuasion On Risk Assessment, Casey L. Smith

Doctoral Dissertations and Master's Theses

Cognitive biases influence decisions and the analyses of risk. They are often derived from two separate processes: bias based on familiarity (familiarity bias) and bias as the result of influences from outside sources (persuasion bias). Research suggests that familiarity-based bias may lead to acceptance of an activity's drawbacks and a leniency of its risks.

In addition, research has tried to measure and analyze different types of biases individually, but few have compared the interactions of more than one bias at once. Because different biases may derive from different mental phenomena it is important to tease out the distinctions, and observe …

An Experimental Investigation Of Glare And Restructured Fiber Metal Laminates, Adelina Vanessa Benedict

Doctoral Dissertations and Master's Theses

Fiber Metal Laminates (FMLs) are a group of materials fabricated by bonding glass/epoxy layers within metal layers. This class of materials can provide good mechanical properties, as well as weight savings. An FML known as Glass Laminate Aluminum Reinforced Epoxy (GLARE) was studied. An experimental investigation comprising of microscopy and tensile testing was carried out using different grades of GLARE. Microscopy revealed the construction details of GLARE, while tensile testing provided means of measuring and analyzing its stress-strain responses. Next, different metal surface pretreatment methods were explored. These included sandblasting, Phosphoric Acid Anodizing (PAA), and AC-130 Sol-Gel treatment. Woven S-2 …

Spacecraft And Propulsion Technician Error, Daniel Clyde Schultz

Doctoral Dissertations and Master's Theses

Commercial aviation and commercial space similarly launch, fly, and land passenger vehicles. Unlike aviation, the U.S. government has not established maintenance policies for commercial space. This study conducted a mixed methods review of 610 U.S. space launches from 1984 through 2011, which included 31 failures. An analysis of the failure causal factors showed that human error accounted for 76% of those failures, which included workmanship error accounting for 29% of the failures. With the imminent future of commercial space travel, the increased potential for the loss of human life demands that changes be made to the standardized procedures, training, and …

High-Fidelity Modeling Of Airfoil Interaction With Upstream Turbulence, Jacob Brodnick

Doctoral Dissertations and Master's Theses

To supplement past research on low speed unsteady airfoil responses to upstream disturbances, this work proposes and investigates a method to generate a turbulent momentum source to be convected downstream and interact with an SD7003 airfoil in a high-fidelity numerical simulation. A perturbation velocity field is generated from a summation of Fourier harmonics and applied to the forcing function in the momentum terms of the Navier Stokes Equations. The result is a three-dimensional, divergence-free, convected turbulent gust with applied statistical parameters. A parametric study has been done in 2D and 3D comparing the resultant flow fields and airfoil interactions for …

The Development Of A Force Balance For Testing Micro Aerial Vehicles, Michael Christopher King

Doctoral Dissertations and Master's Theses

The purpose of this work was to create a six degree of freedom balance that could produce meaningful data for micro aerial vehicles. Research was conducted to investigate the common balance configurations, and the strengths and weaknesses of each configuration were used to select the most appropriate design. The limitations of available fabrication facilities, the desired level of performance and the end user of the balance were all considered to finalize the design. The balance and data acquisition system were fabricated over a period of several months, and unforeseen design issues were handled forthwith. Rigorous calibration and testing processes were …

Design And Optimization Of A Deflagration To Detonation Transition (Ddt) Section, Francisco X. Romo

Doctoral Dissertations and Master's Theses

Throughout the previous century, hydrocarbon-fueled engines have used and optimized the `traditional' combustion process called deflagration (subsonic combustion). An alternative form of combustion, detonation (supersonic combustion), can increase the thermal efficiency of the process by anywhere from 20 - 50%. Even though several authors have studied detonation waves since the 1890's and a plethora of papers and books have been published, it was not until 2008 that the first detonation-powered flight took place. It lasted for 10 seconds at 100 ft. altitude. Achieving detonation presents its own challenges: some fuels are not prone to detonate, severe vibrations caused by the …

Debris Propagation Due To A Space Vehicle Breakup At High Altitudes, Juan A. Alvarado

Doctoral Dissertations and Master's Theses

Recently, there has been a surge of interest in the estimation of the extent of the airspace containing falling debris due to a space vehicle breakup. A precise computation of propagation of debris to the ground is not practical for many reasons. There is insufficient knowledge of the initial state vector, ambient wind conditions and the key parameters including the ballistic coecients. In addition, propagation of all debris pieces to the ground would require extensive computer time. In this thesis, a covariance propagation method is introduced for the estimation of debris propagation due to a space vehicle breakup. The falling …

Analysis Of Leo Radiation Environment And Its Effects On Spacecraft's Critical Electronic Devices, Luz Maria Martines Sierra

Doctoral Dissertations and Master's Theses

Spacecraft, space stations, satellites and astronauts are exposed to an increased level of radiation when in space, and it is important to evaluate the risks associated with extended radiation exposures in missions and space travel in general. The thesis focuses on the LEO radiation environment and how the particles in it interact with materials. Using existing empirical models, the exposed dosage due to the LEO space environment radiation sources, as a function of orbital altitude, orbital inclination and duration is studied. The physical processes that can result in failures and long term degradations of electronic devices due to solar radiation, …

State Of The Art Of Piloted Electric Airplanes, Nasa's Centennial Challenge Data And Fundamental Design Implications, Lori Anne Costello

Doctoral Dissertations and Master's Theses

The purpose of this study was to determine the current state of the electric airplane as primarily defined by results from NASA's Green Flight Challenge Competition. New equations must be derived in order to determine the endurance and range for electric airplanes since the standard equations depend upon weight change over a flight and the weight of an electric airplane does not change. These new equations could then be solved for the optimal velocity and altitude which were the two driving factors that could change range and endurance for a given airplane configuration. The best velocity for range and endurance …

Experimental Investigation And Cfd Simulation Of Active Damping Mechanism For Propellant Slosh In Spacecraft Launch Systems, Dhawal Leuva

Doctoral Dissertations and Master's Theses

Motion of propellant in the liquid propellant tanks due to inertial forces transferred from actions like stage separation and trajectory correction of the launch vehicle is known as propellant slosh. If unchecked, propellant slosh can reach resonance and lead to complete loss of the spacecraft stability, it can change the trajectory of the vehicle or increase consumption of propellant from the calculated requirements, thereby causing starvation of the latter stages of the vehicle. Predicting the magnitude of such slosh events is not trivial. Several passive mechanisms with limited operating range are currently used to mitigate the effects of slosh. An …

Innovative Double Bypass Engine For Increased Performance, Sanjivan Manoharan

Doctoral Dissertations and Master's Theses

Engines continue to grow in size to meet the current thrust requirements of the civil aerospace industry. Large engines pose significant transportation problems and require them to be split in order to be shipped. Thus, large amounts of time have been spent in researching methods to increase thrust capabilities while maintaining a reasonable engine size. Unfortunately, much of this research has been focused on increasing the performance and efficiencies of individual components while limited research has been done on innovative engine configurations. This thesis focuses on an innovative engine configuration, the High Double Bypass Engine, aimed at increasing fuel efficiency …

The Propulsive Design Aspects On The World’S First Direct Drive Hybrid Airplane, Ankit Nanda

Doctoral Dissertations and Master's Theses

The purpose of this thesis is to design a safe technology demonstrator by implementing a direct drive propulsion system for a gas-electric hybrid aircraft. This system was integrated on the Embry-Riddle Eco-Eagle for the Green Flight Challenge 2011. The aim of the system is to allow the pilot to use the electric motor as an independent power source to fly the aircraft once at cruise altitude, while having a gas engine to allow for higher power capability.

The system was designed to incorporate the motor and the motor control unit provided by Flight Design and Drivetek AG alongside a Rotax …

Integration Of Unmanned Aerial Systems In Class E Airspace: The Effect On Air Traffic Controller Workload, Jeeja S. Vengal

Doctoral Dissertations and Master's Theses

As technology rapidly advances and our imagination is no longer fantasy but instead reality, the aviation community needs to concentrate on the harsh truth of airspace safety. In the situation of integrating unmanned aerial systems (UASs) into the National airspace, UASs outside of terminal areas would generally be permitted to fly their preferred routes, and self-separate, with minimal intervention from air traffic control. From an air traffic control perspective, the integration could raise a number of human performance problems including workload extremes and passive-monitoring demands. One fundamental requirement for operation in the National Air Space is to preserve the safety …

Development Of A Higher-Order Navier-Stokes Solver For Transient Compressible Flows, Arjun Vijayanarayanan

Doctoral Dissertations and Master's Theses

A higher‐order density based Navier‐Stokes solver was developed for 2‐Dimensional flows using the finite volume approach. The Van leer flux‐splitting technique was used to calculate the fluxes. The second‐order spatial accuracy was achieved using the variable extrapolation method developed by Van leer called the Montone Upstream Centered Scheme for Conservation Laws (MUSCL) approach. The code development was done using Matlab. The code was verified using two validation cases. Firstly, subsonic, transonic, and supersonic flows over the 2‐D bump were simulated, and the results of the code were compared to the results from Fluent. Secondly, the shock‐tube problem was chosen, and …

Numerical Analysis Of Gun Barrel Pressure Blast Using Dynamic Mesh Adaption, Sathish Xavier

Doctoral Dissertations and Master's Theses

A Computational Fluid Dynamics (CFD) method has been applied to simulate the pressure blast of the projectile which is launched from a barrel and to investigate the pressure distribution and sound pressure level (dB) along different positions away from the gun axis and towards the fuselage of the aircraft. Fluent was employed to simulate the unsteady flow using dynamic mesh with moving boundary. Most CFD based ballistics-model requires additional thermodynamic functions which must be derived from the Noble-Abel equation of state. The unsteady, axisymmetric Navier Stokes equation systems were numerically solved using the Advection Upstream Splitting Method (AUSM) scheme; with …

Ultimate Compression After Impact Load Prediction In Graphite/Epoxy Coupons Using Neural Network And Multivariate Statistical Analyses, Alexandre David Grégoire

Doctoral Dissertations and Master's Theses

The goal of this research was to accurately predict the ultimate compressive load of impact damaged graphite/epoxy coupons using a Kohonen self-organizing map (SOM) neural network and multivariate statistical regression analysis (MSRA). An optimized use of these data treatment tools allowed the generation of a simple, physically understandable equation that predicts the ultimate failure load of an impacted damaged coupon based uniquely on the acoustic emissions it emits at low proof loads. Acoustic emission (AE) data were collected using two 150 kHz resonant transducers which detected and recorded the AE activity given off during compression to failure of thirty-four impacted …

Preliminary Design Of An Asteroid Hopping Mission, Michael D. Scheppa

Doctoral Dissertations and Master's Theses

In 2010, NASA announced that its new vision is to support private space launch operations. It is anticipated that this new direction will create the need for new and innovative ideas that push the current boundaries of space exploration and contain the promise of substantial gain, both in research and capital.

The purpose of the study is to plan and estimate the feasibility of a mission to visit a number of near Earth asteroids (NEAs). The mission would take place before the end of the 21st century, and would only use commercially available technology. Throughout the mission design process, while …

Translational And Rotational Control Of An Asteroid Orbiting Satellite, Takahiro Kuhara

Doctoral Dissertations and Master's Theses

The objective of this thesis is to analyze an effective control scheme for an asteroid orbiting satellite. The thesis first summarizes the progress made in the dynamics formulation of such satellites and then provides a theoretical framework for the control system design. The control objective is to maintain a nadir pointing attitude on a circular equatorial orbit. Using established control design techniques, feedback laws are constructed to control both rotational and translational motion of the satellite so that the control objective is achieved. Computer simulations are carried out to illustrate the effectiveness of the control laws.

Acoustic Emission Fatigue Crack Monitoring Of A Simulated Aircraft Fuselage Structure, Jeremy James Lucas

Doctoral Dissertations and Master's Theses

The purpose of this research was to replicate the fatigue cracking that occurs in aircraft placed under loads from cyclical compression and decompression. As a fatigue crack grows, it releases energy in the form of acoustic emissions. These emissions are transmitted through the structure in waves, which can be recorded using acoustic emission (AE) transducers. This research employed a pressure vessel constructed out of aluminum and placed under cyclical loads at 1 Hz in order to simulate the loads placed on an aircraft fuselage in flight. The AE signals were recorded by four resonant AE transducers. These were placed on …

Formation Feedback Control Of Uav Flight, Stephen Stegall

Doctoral Dissertations and Master's Theses

This thesis is a study of formation control with autonomous unmanned aerial vehicles using the formation as feedback. There is also an investigation of formation methods presenting insight into different algorithms for formations. A rigid formation is achieved using a proportional-derivative virtual structure with a formation feedback controller. There is an emphasis on stick controlled aerodynamics. The rigid formation is verified by a simulation of a longitudinal model. Formation control ideas are presented for rigid formations.