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Vessel dynamic positioning (DP) systems are based on conventional PID-type controllers and an extended Kalman filter. However, they present a difficult tuning procedure, and the closed-loop performance varies with environmental or loading conditions since the dynamics of the vessel are eminently nonlinear. Gain scheduling is normally used to address the nonlinearity of the system. To overcome these problems, a sliding mode control was evaluated. This controller is robust to variations in environmental and loading conditions, it maintains performance and stability for a large range of conditions, and presents an easy tuning methodology. The performance of the controller was evaluated numerically and experimentally in order to address its effectiveness. The results are compared with those obtained from conventional PID controller.

A Dynamic Positioning System (DPS) is a complex control system composed of several algorithms, such as controllers, filters and optimal thrust allocation. The design, analysis and performance prediction of a DPS is normally done by a combination of static and dynamic numerical simulations and tank tests with a reduced model. After that, a long commissioning time is required to adjust control and filter parameters. This paper presents a computational dynamic simulator for DP systems, developed in a R&D project carried out at USP, called Numerical Offshore Tank (NOT). Some features of the simulator are the high speed calculation, thanks to a 120 processor cluster and the presentation of the results in a real time 3D-stereo visualization system. Furthermore, important parameters of the operation can be altered during the simulation, emulating a real DP console. It enables the simulation of most of a typical ship manoeuvering with DP especially those related to the offshore oil industry. Regarding offloading, the simulator can deal with multiple body systems taking into account the effects of risers, mooring lines and hawsers, if any. The Newtonian six-degrees-of-freedom model describes the dynamics of each vessel, in which validated models for environmental forces due to current, wind and waves are included. In order to pre-validate the simulator, a simplified experiment was set-up, composed of a reduced model of a DP tanker with 3 thrusters. Several experiments were carried out, and a detailed comparison with simulation results has shown very good agreement. Two loading conditions were considered: under the action of wind and current and the absence of both.

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Compiled with the help of an internationally acclaimed panel of experts, the Ocean Engineering Handbook is the most complete reference available for professionals. It offers you comprehensive coverage of important areas of the theory and practice of oceanic/coastal engineering and technology. This well organized text includes five major sections: Marine Hydro Dynamics and Vehicles Control, Modeling Considerations, Position Control Systems for Offshore Vessels, Applications of Computational Intelligence in the Ocean's Environment, and Fiber Optics in Oceanographic Applications. Designed to be used as a traditional handbook, it thoroughly covers position control theory and implementations and offers a close look at the present state of ocean engineering. With 200 tables and over 100 figures, the Ocean Engineering Handbook will give you a head start in many aspects of oceanic engineering.

  • Odd Magnus Faltinsen Odd Magnus Faltinsen

The book introduces the theory of the structural loading on ships and offshore structures caused by wind, waves and currents, and goes on to describe the applications of this theory in terms of real structures. The main topics described are linear-wave induced motions, loads on floating structures, numerical methods for ascertaining wave induced motions and loads, viscous wave loads and damping, stationkeeping and water impact and entry. The applications of the theoretical principles are introduced with extensive use of exercises and examples. Applications covered include conventional ships, barges, high speed marine vehicles, semisubmersibles, tension leg platforms, moored or dynamic positioned ships, risers, buoys, fishing nets, jacket structures and gravity platforms. One aim of the book is to provide a physical understanding through simplified mathematical models. In this way one can develop analytical tools to evaluate results from test models, full scale trials or computer simulation, and learns which parameters represent the major contributions and influences on sea loads.

  • Jaroslaw Artyszuk

Some essential aspects of mathematical modelling the uniform current dynamic impact on ship manoeuvring are discussed and assessed. a simulation of a pure drift, and such a drift coupled with a turning motion is next performed for a small tanker. The one-knot current gives rise to the maximum yaw velocity of order fifteen degrees per minute associated however with a relatively long response time. in the shiphandling practise, ship manoeuvring simulation (waterway design, development of safe and efficient shiphandling strategies for masters and pilots under given environmental circumstances), and finally in the mathematical model- based ship automatic control of ship manoeuvres. In the most general case the current is really non-uniform and non-stationary. The latter is however get round by the practically adequate quasi-stationary assumption. An alteration in both magnitude and direction and in a vertical profile (for deep draft vessels in shallow waters, where the current vanishes near the bottom) is commonly regarded while dealing with the non-uniform sea current effect. Moreover, the same spatial distribution of the current affects different ships quite unlikely, dependent upon their size and the underwater hull shape- longer ships are usually more sensitive under normal horizontal gradients of the current. For simplicity purposes, an average current is often adopted being more or less adequate in particular applications. In the aspect of ship hydrodynamics, the influence of local transverse cross- current velocity (in ship's body axes) on the sectional (elementary) sway force and yaw moment, and thus the effect of the lateral velocity total spreading upon the resulting force and moment, is rarely known in the reliable way. Such a research is presently rather a field of the computational fluid dynamics than the physical scale model platform.

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A comprehensive and extensive study of the latest research in control systems for marine vehicles. Demonstrates how the implementation of mathematical models and modern control theory can reduce fuel consumption and improve reliability and performance. Coverage includes ocean vehicle modeling, environmental disturbances, the dynamics and stability of ships, sensor and navigation systems. Numerous examples and exercises facilitate understanding.

  • Thor I. Fossen Thor I. Fossen

The technology of hydrodynamic modeling and marine craft motion control systems has progressed greatly in recent years. This timely survey includes the latest tools for analysis and design of advanced guidance, navigation and control systems and presents new material on underwater vehicles and surface vessels. Each section presents numerous case studies and applications, providing a practical understanding of how model-based motion control systems are designed. With an appropriate balance between mathematical theory and practical applications, academic and industrial researchers working in marine and control engineering aspects of manned and unmanned maritime vehicles will benefit from this comprehensive handbook. It is also suitable for final year undergraduates and postgraduates, lecturers, development officers, and practitioners in the areas of rigid-body modeling, hydrodynamics, simulation of marine craft, control and estimation theory, decision-support systems and sensor fusion.

  • Asgeir J. Sørensen Asgeir J. Sørensen

Offshore exploration and exploitation of hydrocarbons have opened up an era of dynamically positioned (DP) vessels. DP control systems maintain floating structures in fixed position or pre-determined track for marine operation purposes exclusively by means of active thrusters. There are more than 2000 DP vessels of various kind operating worldwide. This paper gives a survey of some of the major technology advances in the DP controller design having taken place during more than 30years of research and development. In addition some perspectives for the future with corresponding research challenges will be addressed.

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