Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Includes bibliographical references. / by J. Kim Vandiver. / Ph.D.

This thesis is concerned with robust control of an offshore steel jacket platform subject to nonlinear wave-induced forces. Since time delay and uncertainty are inevitably encountered for an offshore structure and their existence may induce instability, oscillation and poor performance, it is very significant to study on how the delay and uncertainty affect the offshore structure. In this thesis, a memory robust control strategy is, for the first time, proposed to reduce the internal oscillations of the offshore structure under wave-induced forces, so as to ensure the safety and comfort of the offshore structure. Firstly, when the system's states are adopted as feedback, memory state feedback controllers are introduced for the offshore structure. By using Lyapunov-Krasovskii stability theory, some delay-dependent stability criteria have been established, based on which, and by combining with some linearization techniques, memory state feedback controllers are designed to control the offshore structure. The simulation results show that such controllers can effectively reduce the internal oscillations of the offshore structure subject to nonlinear wave-induced forces and uncertainties. On the other hand, a new Lyapunov-Krasovskii functional is introduced to derive a less conservative delay-dependent stability criterion. When this criterion is applied to the offshore structure, an improved memory state feedback controller with a small gain is obtained to control the system more effectively, which is sufficiently shown by the simulation. Secondly, when the system's outputs are adopted as feedback, memory dynamic output feedback controllers are considered for the offshore structure. By employing a projection theorem and a cone complementary linearization approach, memory dynamic output feedback controllers are derived by solving some nonlinear minimization problem subject to some linear matrix inequalities. The simulation results show that the internal oscillations of the offshore structure subject to nonlinear wave-induced forces are well attenuated. Finally, robust H control is fully investigated for the offshore structure. By employing Lyapunov-Krasovskii stability theory, some delay-dependent bounded real lemmas have been obtained, under which, via a memory state feedback controller or a dynamic output feedback controller, the resulting closed-loop system is not only asymptotically stable but also with a prescribed disturbance attenuation level. The simulation results illustrate the validity of the proposed method.

Graduation date: 1999

Thesis (Ph.D.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 129-136.

Thesis (Ocean E)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1982. / Supervised by J. Kim Vandiver and Henri O. Berteaux. Includes bibliographical references (leaves 151-153).

Thesis (M.Eng.)--Memorial University of Newfoundland, 2000. / Bibliography: leaves [194-197].

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 123-125).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 379-383). Available also in a digital version from Dissertation Abstracts.

This work presents a study of the vernacular boats of modern Greece. A new typology of boats is offered, and an account is given of tools and boatyard practice, design and construction techniques. Evidence for these subjects is drawn from field surveys, museum collections, iconographic studies, and interviews with old boatbuilders. Although most of the information presented comes from the first half of the 20th century, background information from the 18th and 19th centuries is also covered. This longer historical perspective is particularly important in making comparisons between 20th century practices and the boatbuilding techniques of the past. There is evidence for the existence of two main periods of technical change in the industry, namely, the late 18th century, when new methods such as lofting were introduced, and the late 19th century, when changes in the wider shipbuilding industry initiated a process of decline in vernacular boatbuilding. At the same time however, a number of older techniques, for example certain moulding methods, survived at least into the first part of the 20th century. This work offers new insights into the design methods involved in the control of hull-form during "skeletonfirst" boatbuilding from the last two hundred years. It also offers an analysis of the structural integrity and strength of vernacular boats and shows how the structure of boats has evolved across time to incorporate new techniques and changes in boat function.

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