Department: Engineering PhD ![[clear]](close-x.png "Remove this limiter")
81 matches in the database.
These are records: 1 - 30.
[1] [2] [3]
1.
Adduri, Phani R.
ROBUST ESTIMATION OF RELIABILITY IN THE PRESENCE OF MULTIPLE FAILURE MODES.
Degree: PhD, Engineering PhD, 2006, Wright State University
► In structural design, every component or system needs to be tested to…
(more)
▼ In structural design, every component or system needs to be tested to ascertain that it satisfies the desired safety levels. Due to the uncertainties associated with the operating conditions, design parameters, and material systems, this task becomes complex and expensive. Typically these uncertainties are defined using random, interval or fuzzy variables, depending on the information available. Analyzing components or systems in the presence of these different forms of uncertainty increases the computational cost considerably due to the iterative nature of these algorithms. Therefore, one of the objectives of this research was to develop methodologies that can efficiently handle multiple forms of uncertainty. Most of the work available in the literature about uncertainty analysis deals with the estimation of the safety of a structural component based on a particular performance criterion. Often an engineering system has multiple failure criteria, all of which are to be taken into consideration for estimating its safety. These failure criteria are often correlated, because they depend on the same uncertain variables and the accuracy of the estimations highly depend on the ability to model the joint failure surface. The evaluation of the failure criteria often requires computationally expensive finite element analysis or computational fluid dynamics simulations. Therefore, this work also focuses on using high fidelity models to efficiently estimate the safety levels based on multiple failure criteria. The use of high fidelity models to represent the limit-state functions (failure criteria) and the joint failure surface facilitates reduction in the computational cost involved, without significant loss of accuracy. The methodologies developed in this work can be used to propagate various types of uncertainties through systems with multiple nonlinear failure modes and can be used to reduce prototype testing during the early design process. In this research, fast Fourier transforms-based reliability estimation technique has been developed to estimate system reliability. The algorithm developed solves the convolution integral in parts over several disjoint regions spanning the entire design space to estimate the system reliability accurately. Moreover, transformation techniques for non-probabilistic variables are introduced and used to efficiently deal with mixed variable problems. The methodologies, developed in this research, to estimate the bounds of reliability are the first of their kind for a system subject to multiple forms of uncertainty.
Advisors/Committee Members: Penmetsa, Ravi C.
Keywords: limit-state; Membership Functions; Failure Probability; limit-state functions; joint failure; system reliability; MPP
More Like This
2.
Aleman, Rafael E.
A Guided Neighborhood Search Applied to the Split Delivery Vehicle Routing Problem.
Degree: PhD, Engineering PhD, 2009, Wright State University
► The classic vehicle routing problem considers the distribution of goods to geographically…
(more)
▼ 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 to potentially reduce the operational costs of the fleet.This study efficiently solves the split delivery vehicle routing problem using three new approaches. In the first approach, the problem is solved in two stages. During the first stage, an initial solution is found by means of a greedy approach that can produce high quality solutions comparable to those obtained with existing sophisticated approaches. The greedy approach is based on a novel concept called the route angle control measure that helps to produce spatially thin routes and avoids crossing routes. In the second stage, this constructive approach is extended to an iterative approach using adaptive memory concepts, and then a variable neighborhood descent process is added to improve the solution obtained. A new solution diversification scheme is presented in the second approach based on concentric rings centered at the depot that partitions the original problem. The resulting sub-problems are then solved using the greedy approach with route angle control measures. Different ring settings produce varied partitions and thus different solutions to the original problem are obtained and improved via a variable neighborhood descent. The third approach is a learning procedure based on a set or population of solutions. Those solutions are used to find attractive attributes and construct new solutions within a tabu search framework. As the search progresses, the existing population evolves, better solutions are included in it whereas bad solutions are removed from it. The initial set is constructed using the greedy approach with the route angle control measure whereas new solutions are created using an adaptation of the well known savings algorithm of Clarke and Wright (1964) and improved by means of an enhanced version of the variable neighborhood descent process. The proposed approaches are tested on benchmark instances and results are compared with existing implementations.
Advisors/Committee Members: Hill, Raymond R.
Subjects: Engineering; Industrial engineering; Operations research; Transportation
Keywords: vehicle routing; split delivery; variable neighborhood descent; adaptive memory; greedy approach; diversification; tabu search
More Like This
3.
Al-Karaeen, Fawaz.
CHARACTERIZING BATTLEFIELD HUMAN DECISION MAKING WITH VALUE FOCUSED THINKING AND RELIABILITY MODELING.
Degree: PhD, Engineering PhD, 2006, Wright State University
► Al-Karaeen, Fawaz Khalil. Ph.D., Department of Industrial, Biomedical, and Human Factors Engineering,…
(more)
▼ Al-Karaeen, Fawaz Khalil. Ph.D., Department of Industrial, Biomedical, and Human Factors Engineering, Wright State University, 2006. Characterizing Battlefield Human Decision Making with Value Focused Thinking and Reliability Modeling. Military officers and soldiers in combat are faced with complex, time-critical decision problems. The battlefield, or combat, environment involves decisive operations under unpredictable and rapidly changing conditions. Decisions in battlefields take place under uncertain, time constrained conditions and in a tactical environment. A battlefield decision maker encounters a dynamic information environment. During combat, individuals gather and consider information from a variety of sources to determine what information is reliable and useful, and what information is not. There is a clear correlation between the decision making process and the value of information feeding that process. This research examines a decision making model applicable to the battlefield space, a reliability of information model, and then a combined model integrating the individual models. The decision making model will exploit the value-focused thinking paradigm. The reliability model will capture information degradation considerations after deriving and defining a new reliability of information concept. The combined model will provide a means to capture and examine the dynamics of battlefield decision making by linking the value-focused thinking model and the information reliability model. The linked model (Integrated Model) has more advantages and it is more useful than existing models of battlefield decision making. Each effort represents a novel approach and a unique contribution of this research.
Advisors/Committee Members: Hill, Raymond.
Keywords: DECISION; Fundamental Objectives; Decision Situation; decision maker; reliability of information; maker
More Like This
4.
Amarchinta, Hemanth.
Uncertainty Quantification of Residual Stresses Induced By Laser Peening Simulation.
Degree: PhD, Engineering PhD, 2010, Wright State University
► Advanced mechanical surface enhancement techniques have been used successfully to increase the…
(more)
▼ Advanced mechanical surface enhancement techniques have been used successfully to increase the fatigue life of metallic components. These techniques impart deep compressive residual stresses into the component to counter potentially damage-inducing tensile stresses generated under service loading. Laser Peening (LP) is an advanced mechanical surface enhancement technique used predominantly in the aircraft industry. To reduce costs and make the technique available on a large-scale basis for industrial applications, simulation of the LP process is required. Accurate simulation of the LP process is a challenging task, because the process has many parameters such as laser spot size, pressure profile, and material model that must be precisely determined. In the LP process material is subjected up to strain rates of 106 per second, which is very high compared to conventional strain rates. The importance of an accurate material model increases because the material behaves significantly different at such high strain rates. One of the objectives of this research is to make advancements in the simulation of residual stresses induced by laser peening. Validation of various material models under investigation that could be used in simulation and design is performed. Inverse optimization-based methodology is developed for simulation of residual stresses for materials such as Inconel718. The procedure involves optimizing the model constants for one load case and using the same constants for other load cases. The second aspect of this research is to develop a framework for uncertainty quantification of the residual stress field induced by the LP process by propagation of regression uncertainty. Development methodology includes identification of regression uncertainty as a source of input uncertainty and using the bootstrap method to verify the multivariate normality assumption of the model constant estimates. The propagation of the input uncertainty is performed using Taylor series expansion and sensitivity analysis. A confidence band for the entire residual stress field is obtained and validated using the Monte Carlo analysis.
Advisors/Committee Members: Grandhi, Ramana.
Subjects: Aerospace materials; Mechanical engineering; Mechanics
Keywords: Laser Peening; Residual Stress; Material model; Uncertainty; Regression; Bootstrap
More Like This
5.
Barney, Ian Timothy.
Fabrication and Testing of Hierarchical Carbon Nanostructures for Multifunctional Applications.
Degree: PhD, Engineering PhD, 2012, Wright State University
► Multi-scale hierarchical carbon structures have been developed by growing strongly attached carbon…
(more)
▼ Multi-scale hierarchical carbon structures have been developed by growing strongly attached carbon nanotubes (CNT) on high surface area substrates having open, interconnected porosity. This investigation was developed on cellular carbon foams but the process is equally suitable for other geometries including flat, fibers, and other porous substrates (interconnected). It is also adaptable to other substrate materials such as metals, alloys or ceramic compounds. Multiwalled carbon nanotubes are grown using a floating catalyst chemical vapor deposition (CVD) method after pre-coating the substrate with a silica nano-layer. The silica-coated graphitic substrates are seen to grow 280 times more nanotubes per unit area compared to bare graphite. Detailed spectroscopic and microscopic studies indicate that this significant improvement can be attributed to improved adhesion and distribution of the iron catalysts and enhanced catalytic activity from substrate interactions. Failure analysis of the nanotube layer under several types of loading demonstrates strong adhesion between CNT and substrate, with failure occurring in the underlying substrate. Attachment of carbon nanotubes can result in more than two orders of magnitude increase in specific surface area as independently confirmed by modeling the microstructure and direct surface area measurement using Brunauer-Emmett-Teller (BET) technique. These hierarchical materials are tested as encapsulation structures for phase change materials (PCM). The CNT can act as nanofin radiators enhancing energy exchange between the thermally conductive encapsulation and the PCM, hence improving thermal response time. A heat cell was designed to compare the response times of foam encapsulation with and without CNT. Encapsulation with CNT is found to have and significantly faster thermal response. DSC measurements demonstrate that CNT/foam hierarchical encapsulation provides 15% higher storage of latent heat. The improvements in thermal responsiveness and storage capacity from CNT/foam encapsulation provide 150% higher specific power (W/g) while transferring the heat into the paraffin wax when compared to the foam without CNT.
Advisors/Committee Members: Mukhopadhyay, Sharmila M.
Subjects: Materials Science
Keywords: carbon nanotubes; hierarchical materials; carbon foam; phase change materials; paraffin wax; BET; silica
More Like This
6.
Benanzer, Todd W.
System Design of Undersea Vehicles with Multiple Sources of Uncertainty.
Degree: PhD, Engineering PhD, 2008, Wright State University
► The work performed investigates the system design and optimization of an undersea…
(more)
▼ 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 selection and sizing are performed using the naval design tool SNARC. This program uses a branch and bound technique called the A* algorithm to choose the components that should be used in the system and what size they should be according to the mission profiles provided by the path. The structural analysis is performed using the ABAQUS finite element program to calculate the structural reliability of the system. This module uses the structure sizing data, as well as the hydrodynamic and hydrostatic forces from the mission profile, to calculate the system's reliability with respect to a buckling failure, the most common structural failure in undersea vehicles.
Advisors/Committee Members: Grandhi, Ramana V.
Subjects: Mechanical engineering
Keywords: system design; undersea vehicle design; optimization
More Like This
7.
Bontha, Srikanth.
The Effect of Process Variables on Microstructure in Laser-Deposited Materials.
Degree: PhD, Engineering PhD, 2006, Wright State University
► The ability to predict and control microstructure in laser deposition processes requires…
(more)
▼ The ability to predict and control microstructure in laser deposition processes requires an understanding of the thermal conditions at the onset of solidification. The focus of this work is the development of thermal process maps relating solidification cooling rate and thermal gradient (the key parameters controlling microstructure) to laser deposition process variables (laser power and velocity). The approach employs the well-known Rosenthal solution for a moving point heat source traversing an infinite substrate. Cooling rates and thermal gradients at the onset of solidification are numerically extracted from the Rosenthal solution throughout the depth of the melt pool, and dimensionless process maps are presented for both 2-D thin-wall and bulky 3-D geometries. Results for both small-scale (LENS) and large-scale (higher power) processes are plotted on solidification maps for predicting trends in grain morphology in laser-deposited Ti-6Al-4V. Although the Rosenthal predictions neglect the nonlinear effects of temperature-dependent properties and latent heat of transformation, a comparison with 2-D and 3-D nonlinear FEM results for both small-scale and large-scale processes suggests that they can provide reasonable estimates of trends in solidification microstructure. In particular, both the Rosenthal and FEM results suggest that changes in process variables could potentially result in a grading of the microstructure (both grain size and morphology) throughout the depth of the deposit and that the size-scale of the laser deposition process is important. In addition, the effects of a uniform distributed heat source on melt pool geometry and microstructure is investigated by superposition of the Rosenthal point source solution. In particular, the effect of beam width on melt pool length, melt pool depth, solidification cooling rates and thermal gradients is investigated. These results are also interpreted in the context of a solidification map to investigate the effect of beam width on trends in grain morphology in laser-deposited Ti-6Al-4V. Finally, transient effects near the free edge are investigated in both 2-D thin-wall and bulky 3-D geometries through thermal finite element analysis. Here the effect of transient melt pool behavior on solidification cooling rates and thermal gradients (and thereby the resulting microstructure) is investigated.
Advisors/Committee Members: Klingbeil, Nathan W.
Keywords: Laser Deposition; Ti-6Al-4V; Microstructure; Rosenthal Solution; Solidification Map; Finite Element Modeling; Transient Effects; Distributed Heat Source
More Like This
8.
Brown, Jeffrey M.
Reduced Order Modeling Methods for Turbomachinery Design.
Degree: PhD, Engineering PhD, 2008, Wright State University
► Design of structural components is constrained by both iteration time and prediction…
(more)
▼ 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 improve both iteration time and prediction uncertainty for turbomachinery design. The first develops an error-quantified reduced-order model that predicts the effect of geometric deviations on airfoil forced response. This error-quantified approximation shows significant improvements in accuracy compared to existing methods because of its bias correction and description of random error. The second research area develops a Probabilistic Gradient Kriging approach to efficiently model the uncertainty in predicted failure probability caused by small sample statistics. It is shown that the Probabilistic Gradient Kriging approach is significantly more accurate, given a fixed number of training points, compared to conventional Kriging and polynomial regression approaches. It is found that statistical uncertainty from small sample sizes leads to orders of magnitude variation in predicted failure probabilities. The third research area develops non-nominal and nominal mode Component Mode Synthesis methods for reduced-order modeling of the geometric effects on rotor mistuning. Existing reduced-order methods approximate mistuning with a nominal-mode, or design intent, basis and airfoil modal stiffness perturbation. This assumption introduces error that can be quantified when compared to a finite elment model prediction of a geometrically perturbed rotor. It is shown that the nominal-mode approach can produce significant errors, whereas the non-nominal approach accurately predicts blade-to-blade mistuned response.
Advisors/Committee Members: Grandhi, Ramana.
Subjects: Mechanical engineering
Keywords: Turbine Engine; Reduced Order Modeling; Kriging Mistuning Approximation Eigensensitivity; Component Mode Synthesis; IBR Rotor Blisk Airfoil Blade HCF; forced response; modal analysis; Uncertainty Quantification; Statistical; Confidence
More Like This
9.
Brunsman-Johnson, Carissa Ann.
Development and Evaluation of an Interface Aid to Support Web Based Information Seeking for the Blind Research Study.
Degree: PhD, Engineering PhD, 2011, Wright State University
► Information seeking on websites has become more and more challenging for people…
(more)
▼ Information seeking on websites has become more and more challenging for people who are blind. Screen readers attempt to make that task easier by introducing new commands and functionality but there still exists a fundamental gap in the difficulty for people who are blind compared to their sighted counterparts. This research identifies the strategies used by people who are blind and sighted to create an information seeking model, develop the Keywords Expected for Your Search (KEYS) conceptual model for assisting task performance and evaluate a KEYS prototype of this concept for information search and retrieval. This information seeking model was developed by conducting an initial experiment and then validating the model using data from a similar study. The model defines information searching strategies used for both participants that were sighted and blind. Primary information search strategies for the web were identified. The model demonstrated the primary search strategies in the model were keyword based and are the foundation for information seeking on websites for both groups of participants. The KEYS conceptual model for assisting task performance was developed. It includes rules and a keyword library to support information searching for users who are blind. A KEYS prototype was developed to test the conceptual model. The prototype was implemented by controlling the results of the list of links and virtual find commands, which are two of the more commonly used primary search strategies for users who are blind. The evaluation sought to determine the aids' impact on workload, number of commands used, search success, path direction and time to complete a task. Comparisons of the participants who were blind with and without the KEYS prototype were made as well as comparisons to sighted participants. Age group comparisons and age of blindness onset were also compared. The results of the experiment demonstrated that the KEYS prototype significantly improved information searching for users who are blind by lowering all measured variables. A primary contribution of this research was to demonstrate that providing keyword support improves information searches. Implementing the KEYS can produce a significant difference in how users who are blind search for information on webpages.
Advisors/Committee Members: Narayanan, S.
Subjects: Information Systems
Keywords: web-based information searching, screen reader, JAWS, blind, accessible websites, information seeking aid, keyword aid
More Like This
10.
Cazzell, Gregory A.
Output Impedance in PWM Buck Converter.
Degree: PhD, Engineering PhD, 2009, Wright State University
► In this paper, a method is presented to design a minimum order…
(more)
▼ 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.
Advisors/Committee Members: Kazimierczuk, Marian.
Subjects: Electrical engineering
Keywords: PWM, Buck Converter, Output Impedance, Compensator
More Like This
11.
Chakravarthy, Arvindkumar Ravi.
MODEL AND SOLUTION APPROACHES FOR THE EQUIPMENT SCHEDULING UNDER DISRUPTION PROBLEMS IN USPS MAIL PROCESSING AND DISTRIBUTION CENTERS.
Degree: PhD, Engineering PhD, 2008, Wright State University
► This research addresses the equipment scheduling problem under disruptions in United States…
(more)
▼ 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 problems. Over the years, there have been many research studies that focused on solution of the postal equipment and staff scheduling problems. A comprehensive review of these studies is conducted. In the most general sense, each of the equipment and staff schedule problems can be decomposed temporally so and hierarchical analytic approaches have been adopted. Along the time axis, these studies can be classified into strategic, tactical and operational levels. This thesis focuses on the operational equipment scheduling problem or equipment scheduling under disruptions and addresses the adjustment of production plans and workforce schedules through the use of overtime and flexible employees in the face of disruptions such as demand fluctuation and absenteeism that happen on a daily basis and may significantly change demand and the size of workforce. This problem is modeled as a large-scale integer program, which contains equipment scheduling, shift scheduling and overtime management, and break assignment modules. Comprehensive experiments have been designed to investigate the effects of the use of overtime, the control of absenteeism, and the importance of integrating equipment and workforce scheduling simultaneously. The model integrates seamlessly with other research studies and provides the necessary tools to manage the resources in a facility on a routine basis. To improve computational time, an efficient LP based decomposition algorithm has been developed. The algorithm uses linear programming solutions as target solutions to construct a local search process to examine neighboring integer solutions. The heuristic was first proposed for the equipment scheduling under disruptions and then extended to the staff scheduling problem where multiple diverse initial solutions were generated to cover the solution landscape. These heuristics were computational efficient and were able to quickly obtains high-quality feasible solutions and delivers final solutions on par with the state of the art branch and bound algorithm in the solution of integer programs.
Advisors/Committee Members: Zhang, Xinhui.
Subjects: Management; Operations research
Keywords: Postal Operations, Equipment Scheduling, Workforce Scheduling, Overtime Management, Integer Programming
More Like This
12.
Chakravarthy, Vasu D.
Evaluation of Overlay/Underlay Waveform via SD-SMSE Framework for Enhancing Spectrum Efficiency.
Degree: PhD, Engineering PhD, 2008, Wright State University
► Recent studies have suggested that spectrum congestion is mainly due to the…
(more)
▼ 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. The hierarchical access model envisions primary licensed bands, to be opened up for secondary users, while inducing a minimum acceptable interference to primary users. Spectrum overlay and spectrum underlay technologies fall within the hierarchical model, and allow primary and secondary users to coexist while improving spectrum efficiency. Spectrum overlay in conjunction with the present CR model considers only the unused (white) spectral regions while in spectrum underlay the underused (gray) spectral regions are utilized. The underlay approach is similar to ultra wide band (UWB) and spread spectrum (SS) techniques utilize much wider spectrum and operate below the noise floor of primary users.Software defined radio (SDR) is considered a key CR enabling technology. Spectrally modulated, Spectrally encoded (SMSE) multi-carrier signals such as Orthogonal Frequency Domain Multiplexing (OFDM) and Multi-carrier Code Division Multiple Access (MCCDMA) are hailed as candidate CR waveforms. The SMSE structure supports and is well-suited for SDR based CR applications. This work began by developing a general soft decision (SD) CR framework, based on a previously developed SMSE framework that combines benefits of both the overlay and underlay techniques to improve spectrum efficiency and maximizing the channel capacity. The resultant SD-SMSE framework provides a user with considerable flexibility to choose overlay, underlay or hybrid overlay/underlay waveform depending on the scenario, situation or need. Overlay/Underlay SD-SMSE framework flexibility is demonstrated by applying it to a family of SMSE modulated signals such as OFDM, MCCDMA, Carrier Interferometry (CI) MCCDMA and Transform Domain Communication System (TDCS). Based on simulation results, a performance analysis of Overlay, Underlay and hybrid Overlay/Underlay waveforms are presented. Finally, the benefits of combining overlay/underlay techniques to improve spectrum efficiency and maximize channel capacity are addressed.
Advisors/Committee Members: Shaw, Arnab.
Subjects: Electrical engineering
Keywords: Dynamic Spectrum Access, Cognitive Radio, Overlay waveform, Underlay waveform, Software defined radio
More Like This
13.
Cherukuri, Balakrishna.
Microstructural Stability and Thermomechanical Processing of Boron Modified Beta Titanium Alloys.
Degree: PhD, Engineering PhD, 2008, Wright State University
► One of the main objectives during primary processing of titanium alloys is…
(more)
▼ 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 were used in this investigation. Significant grain refinement of the as-cast microstructure and precipitation of TiB whiskers along the grain boundaries was observed with boron additions. Beta21S and Beta21S-0.1B alloys were annealed above the beta transus temperature for different times to investigate the effect of boron on grain size stability. The TiB precipitates were very effective in restricting the beta grain boundary mobility by Zener pinning. A model has been developed to predict the maximum grain size as a function of TiB size, orientation, and volume fraction. Good agreement was obtained between model predictions and experimental results. Beta21S alloys were solution treated and aged for different times at several temperatures below the beta transus to study the kinetics of alpha precipitation. Though the TiB phase did not provide any additional nucleation sites for alpha precipitation, the grain refinement obtained by boron additions resulted in accelerated aging. An investigation of the thermomechanical processing behavior showed different deformation mechanisms above the beta transus temperature. The non-boron containing alloys showed a non-uniform and fine recrystallized necklace structure at grain boundaries whereas uniform intragranular recrystallization was observed in boron containing alloys. Micro-voids were observed at the ends of the TiB needles at high temperature, slow strain rates as a result of decohesion at the TiB / matrix interfaces. At low temperatures and faster strain rates micro voids were also formed due to fracture of TiB needles. Finite element analysis on void formation in TiB containing alloys were in agreement with experimental observations. Microhardness and tensile testing of as-cast + forged and aged Beta21S and Ti5553 alloys with and without boron did not show any significant differences in mechanical properties. The primary benefits of boron modified alloys are in as-cast condition.
Advisors/Committee Members: Srinivasan, Raghavan.
Subjects: Aerospace materials; Engineering; Materials science; Metallurgy
Keywords: Boron, TiB, Beta Titanium, Beta21S,Ti5553, Thermomechanical processing, Zener pinning
More Like This
14.
Cloud-Buckner, Jennifer M.
Managing Patient Test Data in Primary Care: Developing and Evaluating a System for Test Tracking to Enhance Processes, Safety, and Understanding of Performance.
Degree: PhD, Engineering PhD, 2012, Wright State University
► Patient testing is vital for primary care and serves as a gateway…
(more)
▼ Patient testing is vital for primary care and serves as a gateway to specialty healthcare. Patient safety is worsened when testing orders (e.g., laboratory, imaging orders) are not tracked, results are lost, or abnormal results lack patient notification and follow-up. Non-standardized testing management reduces resilience; affects clinical outcomes; and increases errors, costs, workload, and delays. To address the need for testing management improvements, this research followed four phases in six objectives: (1) In Phase I initial survey, assess perceptions, attitudes, and behaviors of practicing healthcare clinicians and administrators about testing, safety, and technology; (2) In Phase II system design, design a low-cost system prototype that manages primary care testing processes for individual patients, supports safety and resilience, and measures overall clinic testing performance for continuous improvement efforts; (3) In Phase III laboratory experiment, evaluate system prototype for effectiveness in managing testing management processes, including test ordering, results review, notification, and tracking; (4) In Phase III, evaluate effectiveness of technology specifically designed to enforce, support, nurture, and measure safety- including individual safety awareness, attitudes, actions, resilience, and safety culture; (5) In Phase III, evaluate effectiveness of the testing management system prototype for increasing understanding of overall clinic testing performance; (6)In Phase IV clinical review, evaluate a revised prototype with primary care clinicians for its perceived effectiveness and potential for process, safety, and performance improvements. This research resulted in a test management system prototype that was effective in managing and standardizing testing processes; showed effectiveness for some aspects of safety, situation awareness, and resilience; and was effective in developing user understanding of clinic performance in testing processes. This system can be used for future product development. Based on theories of resilience, organizational and safety culture, systems safety, and situation awareness, this research also contributes to an increased understanding of requirements to design health information technology that enforces, supports, nurtures, and measures safety.
Advisors/Committee Members: Gallimore, Jennie J.
Subjects: Engineering; Health Care; Health Care Management; Industrial Engineering; Information Technology
Keywords: testing management, clinic management, situation awareness, resilience, patient safety, quality of health care, delivery of health care, primary health care
More Like This
15.
Daily, Jeremy S.
Dissipated Energy at a Bimaterial Crack Tip Under Cyclic Loading.
Degree: PhD, Engineering PhD, 2006, Wright State University
► A new theory of fatigue crack growth in ductile solids has recently…
(more)
▼ A new theory of fatigue crack growth in ductile solids has recently been proposed based on the total plastic energy dissipation per cycle ahead of the crack. This, and previous energy-based approaches in the literature, suggest that the total plastic dissipation per cycle can be closely correlated with fatigue crack growth rates under mode I loading. The goal of the current research is to extend the dissipated energy approach to steady-state crack growth under mixed-mode I/II loading conditions, with application to cyclic delamination of ductile bimaterial interfaces. Such systems can occur in brazing, soldering, welding, and a variety of layered manufacturing applications, where high-temperature material deposition can result in a mismatch in mechanical properties between the deposited material and the substrate. The total plastic dissipation per cycle is obtained by 2-D elastic-plastic finite element analysis of a stationary crack in a general mixed-mode specimen geometry under constant amplitude loading. Numerical results for a dimensionless plastic dissipation per cycle are presented over the full range of relevant material combinations and mixed-mode loading conditions. Results suggest that while applied mode-mix ratio is the dominant parameter, mismatches in yield strength and hardening modulus can have a significant effect on the total plastic dissipation per cycle, which is dominated by the weaker/softer material. Results extended to general elastic-plastic mismatches provide substantial insight into the effects of crack-tip constraint, material hardening behavior and applied mode-mix ratio on the dissipated energy during fatigue crack growth. A consistent definition of the mode mix ratio is presented based on minimizing the elastic strain energy at a crack tip. Next, application of the current theory is demonstrated for thermomechanical fatigue of bonded bimaterials. Finally, the plastic dissipation computations are erformed in a probabilistic framework in an attempt to assess the variability of the fatigue crack growth rate based on variation in bulk properties.
Advisors/Committee Members: Klingbeil, Nathan W.
Subjects: Engineering, Mechanical
Keywords: fatigue, fracture, bimaterials, plastic dissipation, crack growth rate
More Like This
16.
D'Angelo, Maurissa S.
Analysis of Amputee Gait using Virtual Reality Rehabilitation Techniques.
Degree: PhD, Engineering PhD, 2010, Wright State University
► This research shows promise in becoming a standard practice for long term…
(more)
▼ This research shows promise in becoming a standard practice for long term amputee rehabilitation. Exceptional rehabilitation is not universally available to all disabled individuals due to circumstances which limit patient care such as a limited number of trained personnel, limited access to therapy in remote areas, limited patient feedback, limited visits under insurance policies and differing expertise of personnel. Providing real-time, objective feedback will help to continuously improve the quality of life of amputee individuals and provide standardized baseline techniques. The research described in this dissertation expands the use of virtual reality systems to amputee rehabilitation. A virtual reality system with performance metrics was designed, developed and tested. The effectiveness of real-time feedback through self visualization was investigated. This virtual reality system integrated real-time kinematic data into a virtual reality system. Subjects participated in a baseline session, three intervention sessions and a final training session. This Virtual Reality Rehabilitation (VRR) study, incorporating real-time feedback and objective performance metrics, provided a successful baseline demonstration for future research using VRR to improve gait techniques and enable more efficient and effective rehabilitation for amputees and other disabled individuals. To the knowledge of the dissertation team, this was the first study documenting a successful VRR gait-based strategy in patients with lower limb amputations.
Advisors/Committee Members: Reynolds, David.
Subjects: Biomedical research; Engineering; Health care; Rehabilitation
Keywords: virtual reality, rehabilitation, amputee rehabilitation
More Like This
17.
Fendley, Mary E.
Human Cognitive Biases and Heuristics in Image Analysis.
Degree: PhD, Engineering PhD, 2009, Wright State University
► Humans often employ cognitive heuristic principles when making decisions. These cognitive heuristic…
(more)
▼ Humans often employ cognitive heuristic principles when making decisions. These cognitive heuristic principles allow the human to simplify the decision making task, and can, by their very nature, lead to deviations, referred to as cognitive biases, which influence the quality of the decisions.While the role of heuristics and biases have been studied in judgmental decision making tasks, very little research on cognitive heuristics and biases has been done on decision making in complex, dynamic tasks. The research undertaken and discussed herein investigates the existence and impact of cognitive biases in time-critical decision making. To do so, this research uses the target identification task undertaken by military image analysts. This research had three goals. The first goal was to identify the search strategies commonly employed in the object identification task. The second was to identify heuristics and biases that occur during this complex reasoning task. The third goal was to develop a decision support system that improves decision making performance by successfully mitigating the biases that arise during time-critical decision making. To achieve these goals three experiments were conducted. The first, a preliminary study, was done to verify the potential existence of biases in the object identification task. Once the preliminary study indicated the potential existence of biases, a second study was undertaken to identify which specific biases were present. The information uncovered in the second study was evaluated and based on these results a decision support system was constructed using cognitive engineering principles. This decision support system consisted of three artifacts; an image repository, a message board, and a marking aid. The decision support system was then evaluated in the third study. Additionally, this third study permitted the identification of four specific search strategies commonly employed in the object identification task, including peripheral rings, topographic partitions, systematic scanning, and building blocks. The results of the empirical study show that the use of the decision support system produces statistically significant improved performance across each of the five measured dimensions; time taken to identify the targets, accuracy of identification of actual targets, accuracy of classifying targets by type, number of false positives, and number of biases expressed. The results of the research clearly indicate that a decision support system developed using cognitive engineering principles can successfully mitigate the negative impacts of cognitive biases, and improve performance in object identification tasks. While the decision support system developed here produced significant improvements, this research indicates that further gains can likely be made by refining the decision support system through consideration of the specific search strategies that are used to complete the object identification task.
Advisors/Committee Members: Narayanan, S.
Subjects: Engineering
Keywords: cognitive biases, heuristics, search strategies, decision support
More Like This
18.
Findler, Michael James.
Cognitively Sensitive User Interface for Command and Control Applications.
Degree: PhD, Engineering PhD, 2011, Wright State University
► While there are broad guidelines for display or user interface design, creating…
(more)
▼ While there are broad guidelines for display or user interface design, creating effective human-computer interfaces for complex, dynamic systems control is challenging. Ad hoc approaches which consider the human as an afterthought are limiting. This research proposed a systematic approach to human / computer interface design that focuses on both the semantic and syntactic aspects of display design in the context of human-in-the-loop supervisory control of intelligent, autonomous multi-agent simulated unmanned aerial vehicles (UAVs). A systematic way to understand what needs to be displayed, how it should be displayed, and how the integrated system needs to be assessed is outlined through a combination of concepts from naturalistic decision making, semiotic analysis, and situational awareness literature. A new sprocket-based design was designed and evaluated in this research. For the practical designer, this research developed a systematic, iterative design process: design using cognitive sensitive principles, test the new interface in a laboratory situation; bring in subject matter experts to examine the interface in isolation; and finally, incorporate the resulting feedback into a full-size simulation. At each one of these steps, the operator, the engineer and the designer reexamined the results.
Advisors/Committee Members: Narayanan, S.
Subjects: Industrial Engineering
Keywords: Unmanned aerial vehicles; UAV; Visual Thinking; Naturalistic Decision Making; Situation Awareness
More Like This
19.
Fitch, Robert Carl Jr.
DESIGN, MODELING, FABRICATION AND CHARACTERIZATION OF THREE-DIMENSIONAL FERROMAGNETIC-CORE SOLENOID INDUCTORS IN SU-8 INTERPOSER LAYER FOR EMBEDDED PASSIVE COMPONENT INTEGRATION WITH ACTIVE CHIPS.
Degree: PhD, Engineering PhD, 2010, Wright State University
► Integrated circuit technology continually presses toward higher transistor density and thus smaller…
(more)
▼ Integrated circuit technology continually presses toward higher transistor density and thus smaller dimensions, yet passive components which remain the bulk of the circuit area, surprisingly receive sideline attention. This work addresses a niche area of inductor design as it applies to the 3-dimensional (3-D) integration of active transistors and passive components. Hybrid, 3-D circuits residing on inexpensive silicon substrates can be fashioned using a photosensitive epoxy known as SU-8 serving as the interposer layer between the substrate and in which the passive components are embedded. The active components, which are known-good-chips, are secured with epoxy into deep reactive ion etched pockets in the silicon substrate. The inductors are fabricated in the SU-8 covering the active chips. This technique saves considerable money and increases the yield of 3-D circuits compared with the high cost of monolithic microwave integrated circuits (MMICs). The design of solenoid inductors was simulated using a Matlab model incorporating closed-form equations. Herein, that model was developed and verified against both empirical data from fabricated solenoids and against data from a physical simulator in CoventorWare's 3-D electromagnetic, software. A design of experiments examined the effect of solenoid geometry on inductance, quality factor and AC resistance. Additionally, solenoids were fabricated with ferromagnetic cores in an effort to study the potential of enhancing the inductance and quality factor.
Advisors/Committee Members: Kazimierczuk, Marian.
Subjects: Electrical engineering
Keywords: Integrated inductors, ferromagnetic-core, solenoid, SU-8 interposer, quality factor
More Like This
20.
Fogle, Orelle Ryan.
Human Micro-Range/Micro-Doppler Signature Extraction, Association, and Statistical Characterization for High-Resolution Radar.
Degree: PhD, Engineering PhD, 2011, Wright State University
► Recently, the use of micro-Doppler (µD) radar signatures for classification has become…
(more)
▼ Recently, the use of micro-Doppler (µD) radar signatures for classification has become an area of focus, in particular for the case of dynamic targets where many components are interacting over time. To fully exploit the signature information, individual scattering centers may be extracted and associated over the full target observation. Due to the complexity of the target signature, the automated analysis is very difficult. However, the availability of ultra-fine resolution or micro-range (µR) resolution along with target scattering knowledge, can aid this process immensely. Here, we describe a feature extraction algorithm which utilizes both µD and µR data. We apply this algorithm to measured data to gain knowledge of dismount-radar phenomenology. Specifically, we associate µD/µR features to physical human components resulting in an intuitive and physically-relevant model. Additionally, we statistically characterize the radar cross-section (RCS) behavior of the individual body features.
Advisors/Committee Members: Rigling, Brian.
Subjects: Electrical Engineering; Remote Sensing
Keywords: radar; dismount; micro-Doppler; micro-range; radar cross-section
More Like This
21.
Gale, Nicholas C.
FUSION OF VIDEO AND MULTI-WAVEFORM FMCW RADAR FOR TRAFFIC SURVEILLANCE.
Degree: PhD, Engineering PhD, 2011, Wright State University
► Modern frequency modulated continuous wave (FMCW) radar technology provides the ability to…
(more)
▼ Modern frequency modulated continuous wave (FMCW) radar technology provides the ability to modify the system transmission frequency as a function of time, which in turn provides the ability to generate multiple output waveforms from a single radar unit. Current low-power multi-waveform FMCW radar techniques lack the ability to reliably associate measurements from the various waveform sections in the presence of multiple targets and multiple false detections within the field-of-view. Two approaches are developed here to address this problem. The first approach takes advantage of the relationships between the waveform segments to generate a weighting function for candidate combinations of measurements from the waveform sections. This weighting function is then used to choose the best candidate combinations to form polar-coordinate measurements. Simulations show that this approach provides a ten to twenty percent increase in the probability of correct association over the current approach while reducing the number of false alarms in generated in the process, but still fails to form a measurement if a detection form a waveform section is missing. The second approach models the multi-waveform FMCW radar as a set of independent sensors and uses distributed data fusion to fuse estimates from those individual sensors within a tracking structure. Tracking in this approach is performed directly with the raw frequency and angle measurements from the waveform segments. This removes the need for data association between the measurements from the individual waveform segments. A distributed data fusion model is used again to modify the radar tracking systems to include a video sensor to provide additional angular and identification information into the system. The combination of the radar and vision sensors, as an end result, provides an enhanced roadside tracking system.
Advisors/Committee Members: Hong, Lang.
Subjects: Electrical Engineering; Engineering
Keywords: multi-waveform fmcw radar; multi-sensor fusion; target tracking
More Like This
22.
Galigekere, Veda Prakash Nagabhushana.
Stead-State and Small-Signal Modeling of Power-Stage of PWM Z-Source Converter.
Degree: PhD, Engineering PhD, 2012, Wright State University
► Pulse-width modulated (PWM) Z-source converter plays an important role in industrial/power electronic…
(more)
▼ Pulse-width modulated (PWM) Z-source converter plays an important role in industrial/power electronic systems. Steady-state and dynamic modeling of the power-stage of PWM converters is essential for envisaging a closed-loop regulated power supply. Steady-state analysis of pulse-width modulated (PWM) Z-source dc-dc converter operating in continuous conduction mode (CCM) is presented. Voltage and current waveforms, and their corresponding expressions describing the steady-state operation of the PWM Z-source dc-dc converter have been presented. The input-to-output dc voltage transfer functions, both for ideal and non-ideal PWM Z-source dc-dc converter have been derived. The minimum Z-network inductance required to ensure CCM operation is derived. The voltage ripple due to filter capacitor and its ESR, and their individual effects on the overall output voltage ripple have been derived and analyzed. Expressions for power loss in each of the components of the PWM Z-source dc-dc converter has been determined. Using the expressions derived to determine the power losses, an expression for the overall efficiency of the PWM Z-source dc-dc has been derived. An example PWM Z-source dc-dc converter is considered. A laboratory prototype is built and the theoretical analysis is in good agreement with the experimental results. Ac small-signal modeling of pulse-width modulated (PWM) Z-source converter in continuous conduction mode (CCM) by circuit-averaging technique is presented. Averaged dc, low-frequency-large-signal, dc, and ac small-signal models of PWM Z-source converter operating in CCM have been presented. Open-loop power-stage transfer functions corresponding to the capacitor voltage-loop and inductor current-loop are derived. The transfer functions derived take into account the ESRs of the inductors and capacitors. Experimental validation of the derived small-signal models is presented for a laboratory prototype. The theoretical predictions are in good agreement with the experimental results.
Advisors/Committee Members: Kazimierczuk, Marian.
Subjects: Electrical Engineering
Keywords: Small-signal modeling, Z-Source, circuit-averaging, transfer function
More Like This
23.
Ganapathy, Priya.
Development and Evaluation of a Flexible Framework for the Design of Autonomous Classifier Systems.
Degree: PhD, Engineering PhD, 2009, Wright State University
► We have established a modular virtual framework to design accurate, robust, efficient…
(more)
▼ 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 the best classifier; 5) the weighting module judiciously weights the algorithm outputs to fine-tune classifiers, and 6) the cost-function analysis module determines the best detection parameters based on the trade-off between the costs of missed targets and false positive detections. Our solution can be generalized to facilitate detection system design in various applications, including target detection, medical diagnosis, biometrics, surveillance, machine vision, etc. For proof-of-principle, the framework was implemented for the autonomous detection of roadside improvised explosive devices (IEDs). From our set of nine multimodal detection algorithms that yield 1,536 possible classifiers, we identified the single best classifier to accomplish the detection task under a defined cost specification. System performance was tracked through each module and compared to standard approaches for system definition. Algorithm parameter optimization improved performance by an average of 18% (range of 3-32%). Our F2 DM-based classifier selection module predicted classifier performance with an average difference of 3% (standard deviation = ± 2%) from ROC area under the curve (AUC) predictions and an associated computational efficiency improvement of 83%. Adoption of the fusion recommendation yielded 20% improvement over the best-performing algorithm. The weighting module further improved performance of top classifiers by 6% (range of 1-11%). The operating threshold provided by the cost-analysis delivered a true detection rate of 92% and a false detection rate of 14%. In summary, our framework autonomously and expeditiously identified and systematically tuned the detection system to yield an aggregate performance improvement of 43% over a reasonable baseline system (ROC-AUC = 0.93 and 0.65, respectively).
Advisors/Committee Members: Skipper, Julie.
Subjects: Biomedical research; Electrical engineering; Engineering; Health care; Information Systems; Remote sensing; Scientific imaging; Systems design
Keywords: Autonomous classifier selection; ROC analysis; Double-fault measure; Surrogate classifier-selection metric; Weighting algorithm; Decision-Level fusion schemes; Automated target recognition; Pattern recognition; Computer-aided diagnosis; Classifier design
More Like This
24.
Ganti, Satya Rama Naga Lakshmi.
Characterization and Modelling of Laser Micro-Machined Metallic Terahertz Wire Waveguides.
Degree: PhD, Engineering PhD, 2012, Wright State University
► Terahertz radiation, a region in the electromagnetic spectrum which lies between the…
(more)
▼ Terahertz radiation, a region in the electromagnetic spectrum which lies between the microwave and infrared, has gained considerable attention recently due to interesting properties exhibited by materials exposed to this radiation. Dielectric materials such as glass, paper, plastic, and ceramics that are usually opaque at optical frequencies are transparent to terahertz radiation. This led to interesting terahertz spectroscopy and imaging applications. Finite element method simulations of plain, tapered and periodically corrugated metal terahertz wire waveguides have been conducted at the end of the waveguides. This modeling was used to guide the choice of design parameters for the fabrication of waveguides with laser micromachining. The waveguides were characterized with a fiber-coupled terahertz time-domain spectroscopy and imaging system. The THz pulses emitted at the transmitter excite the surface plasmon polaritons in the metal waveguide and propagate as surface waves that are detected at the receiver. This work involved studying the propagation properties as well as the frequency dependent diffraction at the end of the wire waveguides. The temperature dependent propagation properties of the waveguides have also been studied. The THz waveguide properties propagating along the surface of the plain, corrugated and tapered wire waveguides have been successfully demonstrated using both simulations and experimental work.
Advisors/Committee Members: Deibel, Jason.
Subjects: Materials Science; Physics
Keywords: Terahertz wire waveguides, Finite element method, Laser micromachining, Terahertz plasmonics.
More Like This
25.
George, Kiranraj.
Design and Performance Evaluation of 1 Giga Hertz Wideband Digital Receiver.
Degree: PhD, Engineering PhD, 2007, Wright State University
► The lack of a priori knowledge about the waveform of interest, the…
(more)
▼ 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 other major trend in modern receiver signals is the shift towards wider bandwidths. Analog wideband receiver designs can provide accommodation of the technology-stressing bandwidths, but come up to a cost of reduced flexibility. Digital approaches, alternatively, provide flexibility in receiver signal processing, but they are limited by analog-to-digital converter resolution and power consumption. In this dissertation, design and performance evaluation of a 1-GHz signal bandwidth digital receiver, which uses a Kaiser Window function and a compensation technique, is presented. The Kaiser Window reduces the spectral leakage by eliminating the discontinuities at the time window edges and the compensation uncovers the weak signal for extension of the two-signal IDR of the receiver. An exhaustive study of configuration of ADC, FFT, window function, and compensation for a maximum achievable two-signal IDR of the receiver is conducted. It is shown that using a 4-bit ADC and a 256-point FFT of 12-point kernel function, a maximum two-signal IDR of 9 dB is obtained. The IDR is extended to 14 dB by using the Kaiser window and to 18 dB by using the compensation. Furthermore, using a 4-bit ADC and an ideal 256-point FFT, a maximum two-signal IDR of 11 dB is obtained. The IDR is extended to 17 dB by using the Kaiser window and to 22 dB by using the compensation. A combination of both Kaiser window and compensation techniques extends the two-signal IDR of the receiver to 24 dB by using a 12-point kernel function FFT and 29 dB by using an ideal FFT. A novel hardware implementation of the Kaiser window, the compensation technique, and the receiver design is presented.
Advisors/Committee Members: Chen, Henry.
Keywords: wideband digital receiver; two-signal instantaneous dynamic range; receiver signal processing; Kaiser Window function; compensation technique; spectral leakage; Monobit receiver; high precision spectral estimation; Receiver-On-a-Chip
More Like This
26.
Gerschutz, Maria J.
Dynamic Pneumatic Muscle Actuator Control System for an Augmented Orthosis.
Degree: PhD, Engineering PhD, 2008, Wright State University
► This dissertation develops, implements and analyzes a dynamic control system for a…
(more)
▼ 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 feedback, moment/force feedback and adaptive control) are theoretically developed and compared using MATLAB software code. The biomimetic/biomechanical phenomenological model is utilized in the CSCS to characterize the pneumatic muscle actuator. The augmented orthotic application of the physical therapy knee extension task represents the human operator within the CSCS. By implementing the PMA model variations and human operator perturbations, the CSCS is evaluated for each control scheme. The moment/force feedback control outperformed the other schemes by providing accuracy less than ±0.5 degrees. Finally, the dissertation implements the moment/force feedback control scheme on a physical dynamic test system. The dynamic test system contains a commercially available pneumatic muscle actuator. A comparison between open loop control utilizing strictly the phenomenological PMA model and the closed loop control implementing the moment/force feedback is conducted. Statistical analysis concludes that the closed loop method better controls the PMA dynamic nonlinearities associated with displacement. The closed loop method provides significantly lower root mean square error values for all cases analyzed. This research develops and implements a PMA control system utilizing the phenomenological model. It provides an adequate control scheme that responds and compensates for PMA nonlinearities. Additionally, this research provides a unique high-force augmented orthotic application compared to conventional low-force applications. It introduces the use of a commercially available PMA allowing the results to be reproduced and compared. Finally, the research implements a dynamic test system providing time-dependent responses. The PMA dynamic control system presented in this research enhances the potential of PMA applications especially in the rehabilitation, assistive, and aerospace fields.
Advisors/Committee Members: Phillips, Chandler.
Subjects: Biomedical research; Engineering
Keywords: pneumatic muscle; control system; dynamic; moment feedback
More Like This
27.
Gopalakrishnan, Harish.
Energy Reduction for Asynchronous Circuits in SoC Applications.
Degree: PhD, Engineering PhD, 2011, Wright State University
► As complexity increases and gate sizes shrink for monolithic, mixed-signal integrated circuit…
(more)
▼ As complexity increases and gate sizes shrink for monolithic, mixed-signal integrated circuit (IC) technologies, two problems become dominant: substrate noise caused by digital clocks interfering with highly sensitive analog and radio frequency (RF) components and parametric variations that can cause circuit delays to vary in excess of 35%. Clockless logic (or asynchronous) circuits address both of these issues and more. Clockless, asynchronous circuits are by nature delay-insensitive making them immune to parametric variations. Even more important is the processing characteristics of clockless asynchronous circuits, which eliminate highly intricate clock signals that cause large power spikes every time they switch. Consequently, asynchronous design is becoming more and more attractive for low-noise, low-power applications. In a clock free environment, energy is a more relevant metric than power. In this work, we present algorithms that attempt to minimize the energy in asynchronous integrated circuits. Our techniques are based on voltage scaling (VS) and gate sizing (GS). On average, performing a two-stage energy reduction with VS followed by GS results in 26% energy reduction.
Advisors/Committee Members: Emmert, J. M.
Subjects: Electrical Engineering
Keywords: Asynchronous Circuits, Asynchronous Threshold Network Circuits, NULL Convention Logic (NCL), energy reduction, gate sizing, dual voltage scaling
More Like This
28.
Gudmundsson, Karl Solvi.
Multi Dimensional Tracking, Classification, and Training Using Phase Only Filter Pattern Classifier.
Degree: PhD, Engineering PhD, 2004, Wright State University
► Gudmundsson, Karl Solvi, Ph.D., Engineering Ph.D. Program, Department of Elecrical Engineering, (more)
▼ Gudmundsson, Karl Solvi, Ph.D., Engineering Ph.D. Program, Department of Elecrical Engineering, Wright State University, 2004. Multi Dimensional Tracking, Classification, and Training Using Phase Only Filter Pattern Classifier. The only independent variable in electronic computing is time. Optical computing, on the other hand, has inherently two degrees of freedom, the two variables that define a point in a plane. Optical systems always process information in parallel. Such a simple optical element as a lens is capable of performing such a difficult task as a Fourier transform. Therefore, when it comes to pattern classification, optical computing is an attractive option. Dimension reduction and pattern classification from multi sensor data is a challenging exercise. The accepted methods of today's pattern classification of such data require the use of expensive algorithms. Algorithms such as: principal component analysis, linear discriminant analysis, and the k-nearest neighbor to name a few. These methods require significant computation time and are not easily made parallel. The Phase Only Filter (POF) has been shown to be a powerful tool for tracking objects in a two-dimensional plane. In this research, a special tracking technique is developed to overcome weaknesses of the POF under noisy circumstances. The POF is generally implemented in the 2-D plane. However, the POF has neither been trained as a pattern classifier for one dimensional data, nor as a multi-dimensional data classifier. Methods are developed in this work to apply the POF to multi-dimensional pattern classification. Possible optical architecture is also proposed that will allow a parallel realization of the system. Moreover, POF equivalent neural network techniques are devised and implemented for pattern classification. Two level neural network is developed for the case of multi-class classification, and a method of training is developed.
Advisors/Committee Members: Kazimierczuk, Marian K.
More Like This
29.
Hager, Carl H. Jr.
Mechanisms of Nickel-Based Coatings for Fretting Wear Mitigation of Ti6Al4V Interfaces.
Degree: PhD, Engineering PhD, 2008, Wright State University
► Fretting wear is an accumulation of damage that occurs at component interfaces…
(more)
▼ 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 nickel alloy contacts. However, the literature suggests that nickel alloy contacts perform very well in sliding and reciprocating wear contacts at elevated temperatures due to the formation of what is often called a Glaze oxide layer. The current state of literature describes the composition of the glaze layer as NiO. The focus of this dissertation was to provide experimentation and analysis of temperature effects on the lubricious tribofilm formation that occurs in nickel contacts. This was accomplished by testing commercially pure nickel coatings and thick nickel oxide surfaces. The enhanced understanding of the fretting performance of nickel oxides aided in the development of nickel graphite based self-lubricating coatings. These coatings were then proved to reduce fretting wear damage within Ti6Al4V mated surfaces over a wide temperature range.
Advisors/Committee Members: Grandhi, Ramana.
Subjects: Engineering; Experiments; Materials science
Keywords: fretting wear, titanium alloys, Ti6Al4V, nickel, nickel coatings, nickel oxide, high temperature, gross slip
More Like This
30.
Hall, Kara Lynn.
Dynamic Control for a Pneumatic Muscle Actuator to Achieve Isokinetic Muscle Strengthening.
Degree: PhD, Engineering PhD, 2011, Wright State University
► A pneumatic muscle actuator (PMA) is a device that mimics behavior of…
(more)
▼ A pneumatic muscle actuator (PMA) is a device that mimics behavior of skeletal muscle by contracting and generating force in a nonlinear manner when activated. PMAs have a high power to weight ratio and possess unique characteristics which make them ideal for human interaction. Due to their nonlinear dynamics, PMAs are difficult to control, presenting challenges in system implementation. Despite these challenges, PMAs have great potential as a source of resistance for strength training and rehabilitation. The main goal of this work was to control a PMA for use in isokinetic exercise, potentially benefiting anyone in need of optimal strength training through a joint's range of motion. This includes astronauts who need to counteract muscle atrophy and bone loss during prolonged spaceflight. The lightweight PMA driven by pressurized air does not need gravity to produce resistance, making it an attractive option for a microgravity exercise device. The control system developed is based on an inverse three-element phenomenological model and adaptive nonlinear control. The system operates as a type of haptic controller, automatically adjusting resistance to assist a simulated neuromuscular actuator in maintaining the desired velocity. A human quadriceps dynamic simulator (HQDS) was developed so that control effectiveness and accommodation could be tested prior to human implementation. A motor, which produces torque analogous to quadriceps' torque production about the knee, is used in conjunction with the HQDS to simulate neuromuscular actuation. Tracking error results for motor shaft position (simulated joint angle), velocity (simulated lower leg angular velocity), and PMA displacement indicate that the control system is effective at producing PMA displacement and resistance necessary for a scaled, simulated neuromuscular actuator to maintain low-velocity isokinetic movement during simulated concentric and eccentric knee extension. This work is an important step towards human implementation of PMA produced resistance for isokinetic strength training and rehabilitation.
Advisors/Committee Members: Phillips, Chandler.
Subjects: Biomedical Engineering; Engineering; Rehabilitation
Keywords: PMA control, aerospace exercise, microgravity resistive training, rehabilitation, biomimetic actuator
More Like This
[1] [2] [3]
