ABSTRACT
To date, many floating structures have been constructed for different applications such as floating breakwaters, mooring buoys, wave observation buoys, telemetry buoys, oil drilling platforms, floating piers, floating ferry terminals, offshore oil reservoirs, exhibition halls, floating emergency bases and floating bridges (Shirai 1994; Ueda et al. 2002). Water depths at the construction site may vary from a few meters to more than a few kilometers. When designing the station-keeping systemof a floating structure, the actions due to the wind andwaves in a stormyweather and earthquakesmust be considered. The station-keeping system must be designed to restrict the motions of the floating structure within the allowable values which correspond to the purpose and function of the floating structure as well as to ensure that the structure is safe. The station-keeping system of a floating structure may be grouped into
two main types: (1) the mooring-lines type; and (2) the caisson or piletype dolphins with fender system. The station-keeping method by mooring lines uses chains, wire ropes, synthetic ropes, chemical fiber ropes, steel pipe piles and hollow pillar links as shown in Figure 5.1. However, the motions of a floating structure become large when the length of mooring line is rather long. Especially in deep seas, the leg system is adopted to which the pretension is applied to the mooring line in order to restrain heaving motion. In such a station-keeping system, it is difficult to restrain the horizontal motion and usually the mooring lines experience significant tension forces. On the other hand, the dolphin-fenders type is very effective in restraining
the horizontal displacement of the floating structure. As the large-size rubber fenders are able to undergo a large deformation (of up to approximately half their lengths), a considerable amount of the kinetic energy of the floating structure can be absorbed. When a pile structure is used for the dolphin, the energy absorption due to the elastic deformation of the pile is ignored because the deformation of the pile is small in comparison with the rubber fenders. In this case, the reaction forces of the rubber fenders become the design
load for the dolphin. Note that in the dolphin-fender mooring system, the motions in the vertical direction are usually free and thus the fender motions only have the other five components of the rigid-body motion. The dolphin-fender mooring system was first adopted for the two offshore
oil reservoirs at Kamigoto (Ikegami and Shuku 1994) and Shirashima Oil Stockpiling Stations (Ito et al. 1994) in Japan. The mooring system has since been used for other facilities such as floating piers, floating terminals, exhibition halls, floating disaster protection facilities and floating bridges. Figure 5.2 shows rubber fenders attached to the caisson-type dolphin of the Shirashima Oil Stockpiling Station. Figure 5.3 shows the rubber fenders attached to the slab of the Yume-Mai Bridge in Osaka City. Figure 5.4 shows a schematic drawing of the jacket-type dolphin and fender system. For a small floating pier, only piles and roller fenders are used as shown in Figure 5.5. In this chapter, the design and the construction of station-keeping systems
with dolphins will be discussed.
