Thesis (M.A. Sc.)--University of Toronto, 2005.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, 2004. / Thesis Advisor(s): Rudolph Darken, Joseph A. Sullivan. Includes bibliographical references (p. 91-93). Also available online.

Thesis (M.S. in Modeling, Virtual Environments and Simulation)--Naval Postgraduate School, September 2002. / Thesis advisor(s): Rudolph P. Darken, Joe Sullivan. Includes bibliographical references (p. 65-66). Also available online.

Thesis (M.S. in Modeling, Virtual Environments and Simulations)--Naval Postgraduate School, September 2002. / Thesis advisor(s). Includes bibliographical references (p. 79-80). Also available online.

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This thesis presents one of the first applications of H∞-optimization to the design of controllers for industrial problems. The system considered was an unstable helicopter model, obtained from a large nonlinear simulation (provided by the Royal Aircraft Establishment, Bedford) configured to represent future high performance helicopters. The problem was to design a full authority flight control system, to stabilize the aircraft and decouple the controlled inputs, thus reducing pilot workload. Robustness was a primary issue because of model uncertainty, particularly due to the omission from the design model of higher order rotor dynamics. The optimization problem was based on the minimization of sensitivity (for performance) and control output (for robustness) transfer functions. Simple weighting functions were found to be useful for examining the fundamental performance-versus-robustness trade-off, and to be more effective at shaping the closed loop transfer functions than LQG/LTR techniques. A controller designed for a 4-input, 6-output, 8-state linearized plant model was successfully implemented in a non-linear simulation with rotor dynamics. This stabilized the system and enabled good control for small variations about the design operating point. The 'standard problem', consisting of the plant augmented with weights, had 20 states; the controller had 18, which was much smaller than researchers had been predicting, and it is conjectured that all H∞-optimal controllers will have at most the same number of states as the defining 'standard problem'. An important improvement to the H∞-optimization solution process was the development of a numerically reliable algorithm to perform minimal realization. This algorithm solves for a truncated balanced realization of stable state-space systems that are arbitrarily close to being either uncontrollable and/or unobservable. Depending on the choice of partitioning of the Hankel singular values, it can be used to perform minimal realization, or model reduction, with a guaranteed L∞ error bound.

This thesis presents the design and the stability analysis of a hierarchical controller for unmanned aerial vehicles. We utilize non-linear control methodology to command dynamics of unmanned helicopter which has been divided into slower translational dynamics (outer-loop) and faster orientation dynamics (inner-loop), thus exhibiting hierarchical structure. The attitude angles and position which separately belongs to the inner-loop and the outer-loop can be independently controlled by backstepping control strategy. Stability analysis of the helicopter system including applying dynamics has been illustrated after designing. And relative comparison between linear and nonlinear controllers has been carried out. After studying linear control, nonlinear control and stability analysis of one small-scale helicopter, we think about control strategy of a group helicopter which can be called as consensus control.

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This dissertation focuses on implementing and analyzing advanced methods of model predictive control to control helicopters into stable flight near a ship and perform a soft touchdown from that state. A shrinking horizon model predictive control method is presented which can target specific states at specific times and take into account several important factors during landing. This controller is then used in simulation to perform a touchdown maneuver on a ship for a helicopter by targeting a landed state at a specific time. Increasing levels of fidelity are considered in the simulations. Computational power required reduces the closer the helicopter starts to the landing pad. An infinite horizon model predictive controller which allows simultaneous cost on state tracking, control energy, and control rates and allows tracking of an arbitrary equilibrium to infinity is then presented. It is applied in simulation to control a helicopter initially in a random flight condition far from a ship to slowly transition to stable flight near the ship, holding an arbitrary rough position relative to the ship indefinitely at the end. Three different target positions are simulated. This infinite horizon control method can be used to prepare for landing procedures that desire starting with the helicopter in some specific position in close proximity to the landing pad, such as the finite horizon method of landing control described previously which should start with the helicopter close to the ship to reduce computation power required. A method of constructing a landing envelope is then presented and used to construct a landing envelope for the finite horizon landing controller. A pre-existing method of combining linear controllers to account for nonlinearity is then slightly modified and used on implementations of the finite horizon landing controller to make a control that takes into account some of the nonlinearity of the problem. This control is tested in simulation. / Doctor of Philosophy / This dissertation proposes and, using simulation, analyzes control algorithms and their use on helicopter shipboard operations. Various benefits and advances for controls in this area are suggested, tested, and discussed. The control methods presented and implemented, while not limited to these use cases, are particularly well suited for them. One control algorithm is used for controlling flight near the landing point on a ship and performing a soft touchdown on the ship. The algorithm is tested in simulation. Another algorithm is used to control a helicopter initially in flight far away from the ship to slowly transition to stable flight near the ship, holding a rough position relative to the ship indefinitely at the end. This control could be used to set up the helicopter for later use of the touchdown control. This control is also tested in simulation. A method of quantifying what conditions the touchdown controller has a relatively good chance of successfully landing in is then suggested. The range of conditions for which successful touchdown has a relatively high chance of being achieved along with an analysis of that likelihood is called the landing envelope. Using the landing envelope construction method with numerous simulations, a landing envelope for the touchdown controller is obtained. The touchdown controller assumes that the helicopter’s dynamics are linear. Helicopter dynamics (like most dynamics of real systems) are nonlinear. However, under conditions near the point that dynamics are linearized about, a linear approximation is sufficiently accurate. To improve on the above landing algorithm, a method of combining multiple specific implementations of the touchdown controller to help account for nonlinearity to improve the approximation of the dynamics that the controller assumes is then suggested and performed in simulation.

The study involves a qualitative investigation of undergraduate students' experiences of helicopter parenting. Quantitative research has provided a variety of important insights into this phenomenon as far as the characteristics of helicopter parents, the nature of the helicopter parent-child relationship, and multiple outcomes of helicopter parenting for children. Little qualitative research, however, has been conducted on the general phenomenon helicopter parenting of college-aged children. Much of the phenomenon therefore remains to be investigated qualitatively for other demographic groups of undergraduate students. Purposeful sampling was used to select undergraduate students from a mid-sized, public, four-year M1 university in the mid-Atlantic region of the country. Participants were recruited via email, using a listserv that includes all undergraduate students who attend the institution. Data collection involved the use of in-depth, open-ended qualitative interviews to explore the participants' experiences of the phenomenon. A standardized, open-ended interview format was used, which involved developing all interview questions in advance and asking them in the same way and in the same order for all of the participants. A form of whole text analysis was then used to code the data and develop categories and subcategories from the resulting codes. To establish the credibility of the findings from the current study, the traditional trustworthiness criteria was used but without their commitment to a foundationalist epistemology. Several prominent alternative criteria in contemporary qualitative inquiry were used. The current study has a number of limitations, as well as a variety of potential implications for further research on the helicopter parenting of college-aged children, higher education, and qualitative methodology. The analysis yielded seven major findings: (a) helicopter parenting prior to college can take a variety of forms, (b) helicopter parenting during college can take a variety of forms, (c) other parental characteristics associated with helicopter parenting, (d) personal consequences of helicopter parenting, (e) consequences of helicopter parenting for others and relationships with others, (f) efforts to deal with helicopter parenting, and (g) goals associated with education, career, and helicopter parenting. The implications of the findings for higher education and further research and implications of the study for qualitative methodology are discussed. / Doctor of Philosophy / The study involves a qualitative, interview-based investigation of undergraduate students' experiences of helicopter parenting. Little qualitative research, however, has been conducted on the helicopter parenting of college-aged children, and these studies have dealt with only one facet of the phenomenon or have focused on a specific ethnic group. Purposeful sampling was used to select undergraduate students from a mid-sized, public, four-year M1 university in the mid-Atlantic region of the country. Participants were recruited via email, using a listserv that includes all undergraduate students who attend the institution. Data collection involved the use of in-depth, open-ended qualitative interviews to explore the participants' experiences of the phenomenon. A form of whole text analysis was then used to code the data and develop categories and subcategories from the resulting codes. The limitations and implications for further research on the helicopter parenting of college-aged children, higher education, and qualitative methodology are discussed. The analysis yielded seven major findings in the areas of (a) helicopter parenting prior to college can take a variety of forms, (b) helicopter parenting during college can take a variety of forms, (c) other parental characteristics associated with helicopter parenting, (d) personal consequences of helicopter parenting, (e) consequences of helicopter parenting for others and relationships with others, (f) efforts to deal with helicopter parenting, and (g) goals associated with education, career, and helicopter parenting.