Modeling of Ship Roll Dynamics and Its Coupling with Heave and Pitch
In order to study the dynamic behavior of ships navigating in severe environmental conditions it is imperative to develop their governing equations of motion taking into account the inherent nonlinearity of large-amplitude ship motion. The purpose of this paper is to present the coupled nonlinear equations of motion in heave, roll, and pitch based on physical grounds. The ingredients of the formulation are comprised of three main components. These are the inertia forces and moments, restoring forces and moments, and damping forces and moments with an emphasis to the roll damping moment. In the formulation of the restoring forces and moments, the influence of large-amplitude ship motions will be considered together with ocean wave loads. The special cases of coupled roll-pitch and purely roll equations of motion are obtained from the general formulation. The paper includes an assessment of roll stochastic stability and probabilistic approaches used to estimate the probability of capsizing and parameter identification.
ACTIVE CONTROL OF VERTICAL ACCELERATION WITH T-FOIL AND TRIM TAB SYSTEMS IN A FAST FERRY
This study is concerned with the active T-foil placed near the bow on the keel line of the fast ferry and two active trim tab controls placed at the stern to improve the maritime performance of a fast ferry, whilst improving the comfort and safety of passengers and crew. In the scope of the study, the vertical direction of the fast ferry under the random head waves, heave and pitch motions were taken into account. For the control of T-foil and trim Tabs, PID and LQR control methods were used. The purpose of these controllers is to reduce the acceleration of the heave and pitch motions of the fast ferry by changing the operating angles of the T-foil and trim tab wings. A random wave model was created using the Pierson-Moskowitz model, and simulations were done assuming that the fast ferry was subjected to random head waves. Finally, in order to see the effect of vertical acceleration on passengers, the rate of seasickness (MSI) change of the fast ferry in uncontrolled and controlled states was examined. Mathematical models of fast ferry, T-foil and trim tab and their simulations were carried out in MATLAB / Simulink environment. The simulation results show that T-foil and trim tab Active systems can effectively reduce vertical acceleration by improving heave and pitch motions.
An Introduction to Property Theory: Utilitarian Property Theories
As a leading property law casebook puts it, “[u]tilitarian theory is, without doubt, the dominant view of property today, at least among lawyers.” This is certainly true, but the story is also significantly more complicated. Although utilitarian analysis provides tremendous insight into the institution of property, it raises a number of important questions when treated as a comprehensive theory of property. Moreover, the term utilitarian masks a great deal of intellectual and methodological diversity. Rather than a single utilitarian theory, it is more appropriate to speak of a number of utilitarian (or even utilitarian-influenced) property theories . For our purposes, these utilitarian-influenced theories include many contemporary theories that refer to themselves as economic or welfarist . In this chapter, we will explore the broad outlines of these theories, focusing on their points of overlap and also on key areas of disagreement. A BRIEF INTRODUCTION TO UTILITARIANISM Utilitarianism is a consequentialist moral philosophy, that is, one that judges the rightness and wrongness of actions or rules or institutions by the goodness and badness of the consequences they bring about. Utilitarianism assesses the goodness or badness of consequences in terms of their tendency to maximize utility or welfare. Bernard Williams has observed that “[t]he fathers of utilitarianism thought of it principally as a system of social and political decision,” as opposed to “a system of personal morality.” As Williams correctly notes, it is sometimes hard to keep these two domains apart. Nevertheless, it is plainly as a theory of social choice that utilitarianism has been deployed in the context of property theory.