RESEARCH ON CAPSIZING MECHANISM OF FLOATING STRUCTURES IN COMBINED ENVIRONMENTAL CONDITIONS

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International Maritime Organization (IMO) considered to develop a safety regulation which covers a life raft with sea-anchor, since serious fatality has occured on capsizing of large floating structures or life rafts in combined environmental conditions, such as waves, wind and current. In fact this kind of regulation is discussed without any deep insight of mechanism of capsizing. IMO guarantees the safety of large floating structures considering some margins for reserved buoyancy or taking account of full scale test of life rafts in real severe sea conditions. If the mechanism of capsizing of these floating bodies is made clear, it is possible to evaluate the absolute safety of these floating bodies in severe sea conditions, and we can develop reasonable countermeasures for capsizing of floating bodies.In this project we developed an equation of capsize of floating bodies, and completed the computer code of behavior of floating bodies in time domain in which we take account of mutli-directional waves, line structures such as risers, second order wave excitations and nonlinear hydrodynamic forces derived from separated flow.. Finally we proposed the evaluation method of safety of life raft with sea anchor in which we pointed out the importance of wind lift force that is dominant force for capsizing.