Engineering Commons^™

A Guided Neighborhood Search Applied To The Split Delivery Vehicle Routing Problem, Rafael E. Aleman

Browse all Theses and Dissertations

The classic vehicle routing problem considers the distribution of goods to geographically scattered customers from a central depot using a homogeneous fleet of vehicles with finite capacity. Each customer has a known demand and can be visited by exactly one vehicle. Each vehicle services the assigned customers in such a way that all customers are fully supplied and the total service does not exceed the vehicle capacity. In the split delivery vehicle routing problem, a customer can be visited by more than one vehicle, i.e., a customer demand can be split between various vehicles. Allowing split deliveries has been proven …

An Integrated Simulation Environment Combining Process-Driven And Event-Driven Models, Vishnu Sharma Kesaraju

Browse all Theses and Dissertations

A simulation framework that integrates process-driven and event-driven approaches offers a powerful combination of tools to the modeler. In process-driven simulation models, the system can be represented by block diagrams or system networks through which entities flow to mimic real life system objects. In event-driven models, the system can be represented by event graphs, which focus on the abstraction of the event rather than on observable physical entities. In this research, a simulation environment is proposed that integrates both the approaches, i.e. process and event. One of the main outcomes of working in such an environment is that modelers can …

A Predictive Model Of Cognitive Performance Under Acceleration Stress, Richard Andrew Mckinley

Browse all Theses and Dissertations

Extreme acceleration maneuvers encountered in modern agile fighter aircraft can wreak havoc on human physiology thereby significantly influencing cognitive task performance. Increased acceleration causes a shift in local arterial blood pressure and profusion causing declines in regional cerebral oxygen saturation. As oxygen content continues to decline, activity of high order cortical tissue reduces to ensure sufficient metabolic resources are available for critical life-sustaining autonomic functions. Consequently, cognitive abilities reliant on these affected areas suffer significant performance degradations. This goal of this effort was to develop and validate a model capable of predicting human cognitive performance under acceleration stress. An Air …

Output Impedance In Pwm Buck Converter, Gregory A. Cazzell

Browse all Theses and Dissertations

In this paper, a method is presented to design a minimum order compensator for a PWM buck converter with voltage-mode control that will reduce the closed-loop output impedance to match a specific transfer function. The transfer function for the compensator is rigorously developed. It is shown that a third-order compensator is sufficient to achieve a closed-loop output impedance represented by a first-order transfer function. The method is applied to an example, in which the hardware of the dc-dc converter is realized and tested to verify compliance to system requirements.

Dynamic Kernel Function For High-Speed Real-Time Fast Fourier Transform Processors, Yu-Heng George Lee

Browse all Theses and Dissertations

The fast Fourier transform (FFT) plays a critical role in many modern applications, such as acoustics, optics, telecommunications, wireless sensor networks, location sensing, patient monitoring, speech, signal detection, and image processing. The input dynamic range, data throughput rate, frequency resolution, bandwidth, design flexibility, hardware consumption, and power requirements for the various applications are vastly different, leading to significant research focusing on different aspects of FFT performance improvement.

The proposed dynamic kernel function uses an efficient fixed-point numerical representation of the twiddle factor and replaces the cumbersome multipliers with simple shift-and-add operations to enhance the data throughput rate for high-speed wideband …

Development And Evaluation Of A Flexible Framework For The Design Of Autonomous Classifier Systems, Priya Ganapathy

Browse all Theses and Dissertations

We have established a modular virtual framework to design accurate, robust, efficient and cost-conscious autonomous target/object detection systems. Developed primarily for image-based detection problems, such as automatic target detection or computer-aided diagnosis, our approach is equally suitable for non-image-based pattern recognition problems. The framework features six modules: 1) the detection algorithm module accepts two-dimensional, spatially-coded sensor outputs; 2) the evaluation module uses our receiver operator characteristic (ROC)-like assessment tool to evaluate and fine-tune algorithm outputs; 3) the fusion module compares outputs combined under various fusion schemes; 4) the classifier selection module exploits the double-fault diversity measure (F2 DM) to identify …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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.

Browse all Theses and Dissertations

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

Browse all Theses and Dissertations

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 …

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

Browse all Theses and Dissertations

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 …

Rolling Mill Optimization Using An Accurate And Rapid New Model For Mill Deflection And Strip Thickness Profile, Arif Sultan Malik

Browse all Theses and Dissertations

This work presents improved technology for attaining high-quality rolled metal strip. The new technology is based on an innovative method to model both the static and dynamic characteristics of rolling mill deflection, and it applies equally to both cluster-type and non cluster-type rolling mill configurations. By effectively combining numerical Finite Element Analysis (FEA) with analytical solid mechanics, the devised approach delivers a rapid, accurate, flexible, high-fidelity model useful for optimizing many important rolling parameters. The associated static deflection model enables computation of the thickness profile and corresponding flatness of the rolled strip. Accurate methods of predicting the strip thickness profile …

Design And Performance Evaluation Of 1 Giga Hertz Wideband Digital Receiver, Kiranraj George

Browse all Theses and Dissertations

The lack of a priori knowledge about the waveform of interest, the multitudes of signals the receiver might receive, and the noise energy that occupies the same portion of the frequency spectrum as the signal makes the design of a modern wideband receiver very challenging. Especially, the receiver must be able to detect a weak signal in the presence of a strong one, which requires a high two-signal instantaneous dynamic range (IDR). To fulfill this requirement, the receiver must detect genuine weak signals and avoid the detection of strong signals' sidelobes and noise and spurs generated from the receiver system. …

The Effect Of Configural Displays On Pilot Situation Awareness In Helmet-Mounted Displays, Joseph C. Jenkins

Browse all Theses and Dissertations

The current research utilized configural displays within the domain of aviation to assess what design features of configural displays contribute to the formation of operator situation awareness (SA). Configural displays map system information relevant to operator goals onto geometric shapes called emergent features. An emergent feature is formed from the combination of individual line segments to produce a global feature more perceptually salient and recognized sooner than the individual parts themselves. Configural displays have been shown in previous research to provide better operator performance for integration tasks where multiple pieces of information must be considered at once, yet the design …

High-Speed Low-Voltage Cmos Flash Analog-To-Digital Converter For Wideband Communication System-On-A-Chip, Mingzhen Wang

Browse all Theses and Dissertations

With higher-level integration driven by increasingly complex digital systems and downscaling CMOS processes available, system-on-a-chip (SoC) is an emerging technology of low power, high cost effectiveness and high reliability and is exceedingly attractive for applications in high-speed data conversion wireless and wideband communication systems. This research presents a novel ADC comparator design methodology; the speed and performance of which is not restricted by the supply voltage reduction and device linearity deterioration in scaling-down CMOS processes. By developing a dynamic offset suppression technique and a circuit optimization method, the comparator can achieve a 3 dB frequency of 2 GHz in 130 …