ドルフィン係留浮体の波浪中および地震時の係留力に関する研究

抄録

Of late a lot of emphasis has been given to the design study of very large offshore structures e.g. floating air port, floating oil storage tanks moored with dolphin. But there have been very few studies on the motions and mooring forces of vessels moored with dolphin in waves and specially in case of earthquake. In this paper, the motions and mooring forces of vessels moored with dolphin are investigated experimentally and theoretically. At first, model tests were conducted in regular waves with 2 types of mooring restoring forces having nonlinear characteristics. Also experiments were performed under simulated earthquake motions with linear mooring restoring forces. Theoretical analyses were carried out with the help of two methods, namely, equivalent linealized approximate method in frequency domain and computer simulation in time domain (Runge-Kutta-Gill method). The experimental results were in good agreement with the theoretical analysis based on equivalent linealized approximate method as well as computer simulation in time domain by Runge-Kutta-Gill method. In case of vessels moored in waves, influences on the motions and the mooring forces of the wave height, steady external forces, the characteristics of mooring restoring forces and reflected waves by a berth were discussed on the basis of the results of tank tests and theoretical analyses. Experiments and theoretical analyses were also carried under simulated earthquake conditions. The mathematical model adopted for this theoretical analysis leads to a good agreement between the theoretical and experimental results. It was also found that to withstand forces due to earthquake, the mooring systems of main structures should be designed to have a sufficiently low natural frequency of oscilation with respect to that of seismic motion.