Power electronics is a diverse and multi-disciplinary field with constant opportunities to grow, change, and try new techniques to push the envelope. Immediately following the importance of hardware improvement is working on the algorithms controlling the switches. There are many controllers used in the field, all with their own unique benefits and drawbacks. This document will study the feasibility of adding the "Take-Back-Half" algorithm to the ranks of controllers utilized. This algorithm is a non-linear modification to the PI controller with potential benefits in speed and stability.

The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be "eye-safe" because many people will be present during the structural tests. Consequently, laser light has to be delivered through fiber optics and a significant amount of light is lost. Also, the nature of the composite materials makes laser ultrasonic inspection difficult. The composites of interest are formed from woven layers that are stitched through the laminate thickness and bound in a resin matrix. These materials attenuate ultrasound strongly and exhibit a high degree of scattering.;Generation mechanisms in laser based ultrasound must be better understood to improve generation efficiency and consequently improve the signal-to-noise ratio. Although some experimental and theoretical studies have been conducted to characterize generation mechanisms, more extensive work is needed for composite materials. Specifically, we are concerned with generation mechanisms in thick, stitched composite structures. We describe a theoretical and experimental investigation of laser generated ultrasound in complex composite materials. We first develop a mathematical model describing the thermoelastic generation of ultrasound in a general anisotropic material. We then present a wide range of experimental data investigating the effects of laser and material parameters on the generated ultrasound. We specifically consider the relationship between laser pulse width, laser wavelength, and material composition. Finally, we compare this data to our mathematical model.

In order for an aircraft to remain in stable flight, the center of gravity (CG) of an aircraft must be located in front of the center of lift (CL). As the center of gravity moves rearward, pitch stability decreases and the sensitivity to control input increases. This increase in sensitivity is known as pitch gain variance. Minimizing the pitch gain variance results in an aircraft with consistent handling characteristics across a broad range of center of gravity locations. This thesis focuses on the development and testing of an open loop computer simulation model and a closed loop control system to minimize pitch axis gain variation as center of gravity changes. DATCOM and MatLab are used to generate the open loop aircraft flight model; then a closed loop PD (proportional-derivate) controller is designed based on Ziegler-Nichols closed loop tuning methods. Computer simulation results show that the open loop control system exhibited unacceptable pitch gain variance, and that the closed loop control system not only minimizes gain variance, but also stabilizes the aircraft in all test cases. The controller is also implemented in a Scorpio Miss 2 radio controlled aircraft using an onboard microprocessor. Flight testing shows that performance is satisfactory.

An improved and repeatable method for meshing golf club heads using finite elements in TrueGrid® was developed. Using solid brick elements through the thickness of the club head instead of shell elements better represents the many thickness variations throughout each section of a club head. This method also results in a high quality mesh at the center of the club head sections while still maintaining high quality at the edges. A simulation procedure was also developed to predict the acoustic pressure at a designated point in an acoustic medium of a golf club and ball impact using the BEM and Rayleigh methods in LS-DYNA®. The simulation time and computing power required for the impact are modest, while the acoustic simulation time and computing power are much greater. The Rayleigh method provides an alternative which can greatly reduce these requirements. The simulation of sound produced from the ball and a USGA COR plate, generic driver, and hybrid impact was accomplished with reasonable results. Experimental testing was performed using a USGA plate to validate the plate result. A simple tap test and an air cannon test were performed to record the acoustic response with a microphone. A Fast Fourier Transform was performed to obtain the frequency response. These two tests correlated with each other, indicating that air cannon procedures could be negated in favor of a much simpler tap test during prototype testing for acoustics. The simulation frequency responses showed similar results to the experimental tests, demonstrating that the procedure developed in this project can be a viable and effective method for determining the acoustic response of the golf club and ball impact.

Purpose: The purpose of this research is to examine how Management Control Systems (MCS) impact Diversification Strategy Processes (DSP) in diversified firms. Method: A qualitative research method was used where five different profiled managers participated in the research. The interviews were semi-structured and secondary data were used together with the findings where secondary data was available. Thematic analysis was used throughout the data analysis. Conclusion: The results are inconclusive regarding the impact of the Belief, Interactive, and Diagnostic Controls on the Initiation, Searching, and Execution Stage of DSP. The findings are, however, consistent with the impact of Boundary Controls on the Initiation, Searching, and Execution Stage of DSP. Research Limitations: This research has not differentiated between different types of diversification strategies and their processes. Small, medium, and large firms have not been separated throughout the research. The sample size of the data collection was small, making the results not generalizable.

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Aquaponics has the potential to be a superior food production method compared to traditional agriculture through its potential for sustainability. This is particularly important in advanced aquaponic systems that integrate waste disposal (e.g., kitchen waste) and involve several steps linking waste decomposition to protein production. In such systems a success of one type of organism propagates down the food chain and may have negative impact on contribution of other organisms, which reduces system efficiency. I hypothesised that a combination of top-down and bottom-up regulations, concepts borrowed from resilient natural ecosystems, would allow to optimize environment for aquaponics systems to avoid such negative impacts. First, I conducted an experiment using simplified systems with two trophic levels only to determine productivity, resistance and resilience of the various combinations of top-down and bottom-up forces. The simple systems contained algae and Daphnia magna and were placed under a light removal disturbance to observe the abilities of these different combinations to resist and recover from a generic negative environmental impact. Next, a similar light disturbance was implemented on a large complex aquaponics system to discover if it would react differently from the smaller ones. The resistance and resilience of algae in the small systems was not found to have any relationship to predation. The resilience of algae was better at low nutrient levels compared to high ones. There was evidence that low nutrient treatments had better resistance and resilience of abiotic factors. The larger systems appeared to have inferior resistance and resilience as compared to the simple, small systems. However, a time series analysis indicates that these large systems, in contrast to the simpler systems, actually improved in the amount of algae after the disturbance. New methods for accounting for this in resilience calculations are needed to eliminate potential statistical artifacts that might lead to some of my observations. / Thesis / Master of Science (MSc) / Aquaponics has the potential to be a superior food production method compared to traditional agriculture through its potential for sustainability. This is particularly important in advanced aquaponic systems that integrate waste disposal (e.g., kitchen waste) and involve several steps linking waste decomposition to protein production. In such systems a success of one type of organism propagates down the food chain and may have negative impact on contribution of other organisms, which reduces system efficiency. I hypothesised that a combination of top-down and bottom-up regulations, concepts borrowed from resilient natural ecosystems, would allow to optimize environment for aquaponics systems to avoid such negative impacts. First, I conducted an experiment using simplified systems with two trophic levels only to determine productivity, resistance and resilience of the various combinations of top-down and bottom-up forces. The simple systems contained algae and Daphnia magna and were placed under a light removal disturbance to observe the abilities of these different combinations to resist and recover from a generic negative environmental impact. Next, a similar light disturbance was implemented on a large complex aquaponics system to discover if it would react differently from the smaller ones. The resistance and resilience of algae in the small systems was not found to have any relationship to predation. The resilience of algae was better at low nutrient levels compared to high ones. There was evidence that low nutrient treatments had better resistance and resilience of abiotic factors. The larger systems appeared to have inferior resistance and resilience as compared to the simple, small systems. However, a time series analysis indicates that these large systems, in contrast to the simpler systems, actually improved in the amount of algae after the disturbance. New methods for accounting for this in resilience calculations are needed to eliminate potential statistical artifacts that might lead to some of my observations.

The purpose of this dissertation is to develop a methodology for designing active control laws in a computational aeroelasticity environment. The methodology involves employing a systems identification technique to develop an explicit state-space model for control law design from the output of a computational aeroelasticity code. The particular computational aeroelasticity code employed in this dissertation solves the transonic small disturbance equation using a time-accurate, finite-difference scheme. Linear structural dynamics equations are integrated simultaneously with the computational fluid dynamics equations to determine the time responses of the structural outputs. These structural outputs are employed as the input to a modern systems identification technique that determines the Markov parameters of an "equivalent linear system". The eigensystem realization algorithm is then employed to develop an explicit state-space model of the equivalent linear system. Although there are many control law design techniques available, the standard Linear Quadratic Guassian technique is employed in this dissertation. The computational aeroelasticity code is modified to accept control laws and perform closed-loop simulations. Flutter control of a rectangular wing model is chosen to demonstrate the methodology. Various cases are used to illustrate the usefulness of the methodology as the nonlinearity of the computational fluid dynamics system is increased through increased angle-of-attack changes. / Ph. D.