This paper develops designs for some space-saving additional structures in terms of effective reflection or scattering of incident waves at the weather side of Mega-Floats. In order to reduce hydroelastic response in long waves, numerical analyses are carried out taking into account minimization of vertical diffraction force on the edge of offshore Mega-Floats. A model test is then conducted by using an elastic model with additional structures attached, and the effects are validated. However a new problem, enhancement of horizontal motion, is found to arise due to the additional structures, and methods of approach for restraint of horizontal motion are also discussed.
The Mega-Float, a very large floating pontoon structure, is regarded as a means of infrastructure development in the near future, and design techniques are being developed for feasibility studies. Hydroelastic response in waves is critical in structural design, so conventional Mega-Floats are only set up in relatively calm water behind islands or breakwaters. In the case of a supersized Mega-Float, suitable harbors would be quite limited, and it would be essential to build breakwaters. These problems have meant that floating structures have been unable to demonstrate primary cost performance. Thus, development of devices to widen the range of potential setup sites is important for the realization of offshore Mega-Floats. Requirements are that the concept of progress in antiwave performance of Mega-Floats be made practicable in rather high long waves, that the degree of freedom at adoption setup sites be augmented, and that construction methods for Mega-Float be feasible. Yago et al. (1997) investigated the effects of a wave-reflector and wave-breaker (consisting of a deck, column and submerged horizontal plate) which is attached at the weather side to experimentally reduce hydroelastic response. The demerit of this device is the augmentation of horizontal motion.