Engineering Commons^™

Study Of The Issues Of Computational Aerothermodynamics Using A Riemann Solver, Sean James Henderson

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This work is part of a project to more accurately model hypersonicflow. A number of issues in hypersonic flow are addressed.

The first issue addressed is that of air properties at increased temperatures. In particular the thermodynamic and transport properties of chemical equilibrium air are found for temperatures up to 30,000 K for a pressure range from 1x10-4 to 100 atm. This work provides properties at slightly higher temperatures for the lower pressure region than can be found in the literature. This work also covers adding equilibrium air chemistry to the computational fluid dynamics computer code known as AVUS.

The …

Model And Solution Approaches For The Equipment Scheduling Under Disruption Problems In Usps Mail Processing And Distribution Centers, Arvindkumar Ravi Chakravarthy

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This research addresses the equipment scheduling problem under disruptions in United States Postal Service mail processing and distribution centers. These facilities contain a large variety of equipment and employ a non-homogeneous workforce that work on shifts of various lengths and start times. The scheduling of equipment (the determination of the configuration and usage of equipment to match mail arrivals) and the scheduling of workforce (the determination of the optimal size and composition of the workforce, their days off / lunch assignments, and overtime usage) to meet processing service commitment with a constantly changing demand are some of the most challenging …

Dynamic Characterization Of A Pneumatic Muscle Actuator And Its Application To A Resistive Training Device, Jennifer L. Serres

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Research described in this dissertation expands the use of a biomechanical phenomenological model to a commercially available pneumatic muscle actuator (PMA). Due to the nonlinearities of the device, achieving accurate control is challenging. Experiments have been conducted that define boundaries of operation where linear approximations can be used to describe the dynamics of the PMA. Empirical data presented in this dissertation show that nonlinearities exist more prevalently at higher loads (on average >70% contractile force value). When the PMA is under high loads, low displacement occurs. Therefore, these regions are of less interest to design engineers. Once conditions of nonlinearities …

Reduced Order Modeling Methods For Turbomachinery Design, Jeffrey M. Brown

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Design of structural components is constrained by both iteration time and prediction uncertainty. Iteration time refers to the computation time each simulation requires and controls how much design space can be explored given a fixed period. A comprehensive search of the space leads to more optimum designs. Prediction uncertainty refers to both irreducible uncertainties, such as those caused by material scatter, and reducible uncertainty, such as physics-based model error. In the presence of uncertainty, conservative safety factors and design margins are used to ensure reliability, but these negatively impact component weight and design life. This research investigates three areas to …

Improved Structural Health Monitoring Using Random Decrement Signatures, Oleg V. Shiryayev

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Detection of structural damage phenomena such as cracks, delaminations, or loose fasteners is important because it increases safety and may allow significant reduction in operational costs. Many structural health monitoring techniques are based on detecting changes in vibration features obtained from the measured response. The technique presented in this work is based on the random decrement signatures calculated from the random response. No knowledge of input signal is required. Random decrement signatures have been used for damage detection purposes in the past. The significance of this work is that it explores the possibility of identifying the type of damage and …

Broad Bandwidth High Resolution Analog To Digital Converters: Theory, Architecture And Implementation, Saiyu Ren

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Analog to digital converters (ADCs) translate analog quantities, which are characteristic of most phenomena in the "real world" to digital language for a variety of applications including information processing, computing, communication and control systems. The performance of the digital signal processing and communication systems is generally limited by the speed and precision of the digital input signal which is achieved at the interface between analog and digital information. The analog to digital converter (ADC) has become a critical component for advanced telecommunication systems. The desire to move the analog to digital interface closer to the sensor has resulted in more …

Study Of Multi-Modal And Non-Gaussian Probability Density Functions In Target Tracking With Applications To Dim Target Tracking, Peter V. Hlinomaz

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The majority of deployed target tracking systems use some variant of the Kalman filter for their state estimation algorithm. In order for a Kalman filter to be optimal, the measurement and state equations must be linear and the process and measurement noises must be Gaussian random variables (or vectors). One problem arises when the state or measurement function becomes a multi-modal Gaussian mixture. This typically occurs with the interactive multiple model (IMM) technique and its derivatives and also with probabilistic and joint probabilistic data association (PDA/JPDA) algorithms. Another common problem in target tracking is that the target's signal-to-noise ratio (SNR) …

Mechanisms Of Nickel-Based Coatings For Fretting Wear Mitigation Of Ti6al4v Interfaces, Carl H. Hager Jr.

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Fretting wear is an accumulation of damage that occurs at component interfaces that are subjected to high contact stresses coupled with low amplitude oscillation. The key to fretting wear reduction in metallic contacts is the mitigation of galling at the interface, followed by the control of debris production and the rheology of active wear debris. Once the thin surface species of the metallic interfaces is dispersed, adhesion between the contacting nascent surfaces causes the inception of severe surface deformation and material transfer or removal. This is extremely apparent in the fretting wear of aerospace materials such as titanium alloy and …

Modeling Training Effects On Task Performance Using A Human Performance Taxonomy, Douglas P. Meador

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There is little argument that modern military systems are very complex, both in terms of the resources in time and money to develop them and the infrastructure that is required to produce trained operators. To properly execute human systems integration during the acquisition process, systems built to train operators must be developed that optimize training. Consequently, the training system community would benefit from simulation models that provide the ability to make accurate predictions of training processes, and allow the decision maker to specify an optimum combination of operator performance after training and the cost of that training. The goal of …

Microstructural Stability And Thermomechanical Processing Of Boron Modified Beta Titanium Alloys, Balakrishna Cherukuri

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One of the main objectives during primary processing of titanium alloys is to reduce the prior beta grain size. Producing an ingot with smaller prior beta grain size could potentially eliminate some primary processing steps and thus reduce processing cost. Trace additions of boron have been shown to decrease the as-cast grain size in alpha + beta titanium alloys. The primary focus of this dissertation is to investigate the effect of boron on microstructural stability and thermomechanical processing in beta titanium alloys.

Two metastable beta titanium alloys: Ti-15Mo-2.6Nb-3Al-0.2Si (Beta21S) and Ti-5Al-5V-5Mo-3Cr (Ti5553) with 0.1 wt% B and without boron additions …

A System For Collecting Data To Characterize A Pre-Fall Change In Sway: Development And Proof-Of-Concept Analyses, Amy Renae Sipp

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Falls account for almost two million emergency department visits per year in the U.S. and are the leading cause of injury deaths among adults 65 years of age and older. Despite efforts to reduce fall risk factors, about one-third of community-dwelling older adults fall each year in the U.S. New methods and devices are needed to prevent falls and to reduce morbidity and mortality related to falls. Presently, it is unknown if there is a measurable change in sway before a person falls. In order to find out, a wireless data acquisition system was developed as no existing tools were …

New Heuristic And Metaheuristic Approaches Applied To The Multiple-Choice Multidimensional Knapsack Problem, Chaitr Hiremath

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The knapsack problem has been used to model various decision making processes. Industrial applications find the need for satisfying additional constraints and these necessities lead to the variants and extensions of knapsack problems which are complex to solve. Heuristic algorithms have been developed by many researchers to solve the variants of knapsack problems. Empirical analysis has been done to compare the performance of these heuristics. Little research has been done to find out why certain algorithms perform well on certain test problems while not so well on other test problems. There has been little work done to gain knowledge of …

The Development Of A Nonlinear Phase-Lock Loop With Adaptive Gain Control Based On Modern Control Theory, Michael D. Myers

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As the performance of integrated circuits (IC) improve, a more precise clock-signal is needed to regulate their actions. The primary objective of this dissertation is to improve the phase-lock loop (PLL), which is the most common type of clock-generator. A nonlinear phase-lock loop (NPLL) was developed by adding a nonlinear-gain unit to a standard PLL. The NPLL implementation improves performance compared to existing PLLs by demonstrating faster acquisition times and superior jitter performance. The nonlinear-gain is achieved by the use of a fuzzy controller. The fuzzy controller takes in a value and generates outputs based upon the rules that are …

Dynamic Pneumatic Muscle Actuator Control System For An Augmented Orthosis, Maria J. Gerschutz

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This dissertation develops, implements and analyzes a dynamic control system for a pneumatic muscle actuator (PMA) utilizing an augmented orthosis application. The application of PMAs are limited due to poor control capabilities resulting from dynamic nonlinearities. An adequate control system applying an appropriate dynamic pneumatic muscle actuator model increases the potential utility of PMAs in high-force applications including augmented orthotic applications.

The research conducts an initial analysis evaluating the feasibility of PMAs in high-force applications (force assistance with minimal displacement). A computational simulated control system (CSCS) is developed to analyze three different control schemes. The three PMA control schemes (position …

Expectation-Maximization Optical Tomosynthetic Volume Imaging, Philip M. Hanna

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Optical tomosynthetic imaging of 3-D objects from disparate 2-D images has been limited in the past by a lack of algorithmic enforcement of physical constraints, in particular within-scene obscuration and object self-occlusion. This paper presents a stochastic observation model of a tomosynthetic collection that explicitly includes an obscuration operator that is unknown by the sensor. The expectation-maximization algorithm is used to iteratively estimate the obscuration operator and to reconstruct the 3-D volume of interest. Explicit inclusion of obscuration effects greatly enhances the spatial and spectral accuracy of 3-D results without use of costly post-processing techniques. Performance metrics are introduced and …

Process Variation-Aware Timing Optimization With Load Balance Of Multiple Paths In Dynamic And Mixed-Static-Dynamic Cmos Logic, Kumar Yelamarthi

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The semiconductor technology has been advancing rapidly over the past decade to result in the design of several innovative applications. This advancement of technology with the shrinking device has allowed for placement of billions of transistor on a single microprocessor chip. On the other hand, this shrinking device sizes has presented the design engineers with two major challenges: timing optimization at multiple giga-hertz frequencies, and reducing the daunting effects of semiconductor process variations. Failure to account for these process variations often results in loss of design productivity by one generation, and might even result in design failure.

This research presents …

Composite Membranes For Proton Exchange Membrane Fuel Cells, Jinjun Shi

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Proton exchange membrane fuel cells (PEMFCs), often regarded as a green energy source, have become a promising candidate to replace traditional power sources. One of the obstacles toward commercialization of PEM fuel cells is lack of high performance and low cost proton exchange membranes. The objective of this study was to develop and evaluate higher-performance, Nafion-based composite proton exchange membranes that are suitable for operating at higher temperatures (> 85°C).

Proton exchange membranes were prepared by adding silica and heteropolyacids (HPAs) to a proton-conducting polymer matrix, Nafion. The added silica powder particles, either by direct mixing or sol-gel reaction, were …

System Design Of Undersea Vehicles With Multiple Sources Of Uncertainty, Todd W. Benanzer

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The work performed investigates the system design and optimization of an undersea vehicle. The system design is driven by the available components, the missions the vehicle is required to perform, and the performance the system configuration yields. The system design consists of three design modules: path planning, component selection and sizing, and structural analysis. The path planning module uses a novel application of the Particle Swarm Optimization algorithm named Path Planning by Additive Freedom. Additionally, the unknown aspects of the mission space through which the path propagates are dealt with using an uncertainty quantification method known as Evidence Theory. Component …

A Study Of Multi-Echelon Inventory Systems With Stochastic Capacity And Intermediate Product Demand, Suman Niranjan

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The research in this dissertation involves the study of several multi-echelon inventory systems with stochastic capacity and intermediate product demand. Specifically we analyze the behavior of the system which consists of several intermediate product demands. The analysis is primarily three fold i) developed update (relational) equations for all the multi-echelon inventory systems under several inventory allocation policies, ii) develop two simulation optimization approaches 1) OptQuest framework, and 2) IPA (Infinitesimal Perturbation Analysis) framework, used to minimize the total cost of the inventory systems that satisfy the desired customer service level, iii) obtain numerical results for all the multi-echelon inventory systems …

Evaluation Of Overlay/Underlay Waveform Via Sd-Smse Framework For Enhancing Spectrum Efficiency, Vasu D. Chakravarthy

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Recent studies have suggested that spectrum congestion is mainly due to the inefficient use of spectrum rather than its unavailability. Dynamic Spectrum Access (DSA) and Cognitive Radio (CR) are two terminologies which are used in the context of improved spectrum efficiency and usage. The DSA concept has been around for quite some time while the advent of CR has created a paradigm shift in wireless communications and instigated a change in FCC policy towards spectrum regulations. DSA can be broadly categorized as using a 1) Dynamic Exclusive Use Model, 2) Spectrum Commons or Open sharing model or 3) Hierarchical Access …