Abstract

Based on the traditional catenary mooring, a new mooring system with submerged buoy is proposed. Genetic algorithm is used to optimize the length and weight of the new mooring line to keep the pretension, horizontal span, as well as the length of line resting on the seabed consistent with the traditional catenary mooring. To illustrate the validity of this new system, the static and dynamic characteristics are studied and compared with that of traditional catenary mooring. The piecewise extrapolating method is employed to solve the static problem. The dynamic analysis is executed through time-domain nonlinear finite element method accounting for the sinusoidal oscillations of the moored floating platform. The specific results would be helpful for the design improvement of deep water mooring system

Introduction

Mooring systems are used extensively in the offshore field of applications to position floating drilling or production systems and other marine vehicles. The present mooring systems used are mainly catenary mooring system and taut mooring system.

Catenary mooring system is the most common mooring system in water with a depth less than l500m, which consists of a group of lines combined of chain and wire rope. The restoring force of catenary mooring system is mainly provided by its own weight. There is enough length of mooring line resting on the seabed to avoid the anchor bearing vertical load. With the requirement to operate in increasing water depths, traditional catenary mooring system become more and more unsuitable (Dove et al., 2000). The suspended weight of mooring lines becomes a prohibitive factor, which will not only heighten line tensions at the fairlead but also enlarge vertical load on the vessel. The growth vertical load can be important as it effectively decreases the vessel's payload capacity. Besides, the restoring force provided by catenary mooring system is not adequate to provide small platform offsets with the increase of water depth.

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