Hydroelastic Responses of VLFS Deployed Near Islands and Reefs

Abstract

The rapid expansion of world population, the exhausting of inland resources and the requirement of sustainable development of world economy have strengthened the efforts of mankind to increase the capability of resource exploitation and space utilization in the ocean. Very Large Floating Structures (VLFS) are among those marine structures that have attracted long lasting attention in ocean utilization for several decades. The applications of different size VLFS as floating piers, floating airports, floating hotels, floating fuel facilities and even floating cities have triggered extensive researches. Several projects including the conceptual design and construction of VLFS have been launched, for instance, Mega-Float in Tokyo Bay, Floating oil storage bases in Kamigoto and Shirashima islands, Floating emergency rescue bases in Yokohoma, Floating performance stage in Singapore, Large floating bridge in Norway, Mobile offshore base (MOB) in USA and Multi-purpose floating base near islands in China. Due to much larger dimensions, relatively smaller global rigidities and lower natural frequencies than an ordinary ship, a VLFS has apparent flexible body responses rather than rigid body motions in waves. Hence hydroelastic analyses are of great importance in design and safety assessment of a VLFS. Extensive researches have been carried out during the past decades in the development of prediction methods of hydroelastic responses of VLFSs. However, most publications in this field were for VLFSs in open sea. If a VLFS is deployed near islands and reefs in complicated geographical environment, the wave conditions, wave loads and the hydroelastic responses of a VLFS will be quite different than in open sea. In this paper the three-dimensional hydroelasticity theories that have been widely used in the analysis of a VLFS in deep or shallow open sea with constant water depth are briefly introduced. Based on these theories the numerical approaches of hydroelastic analyses of a VLFS near island and reefs in shallow sea, developed recently by CSSRC, are described. Some important technical problems, including description of wave environment, design scheme, connectors between modules, hydroelastic responses, coupled responses with mooring system and safety analysis of a VLFS deployed near islands and reefs are also discussed.