RESEARCH ON CAPSIZING MECHANISM OF FLOATING STRUCTURES IN COMBINED ENVIRONMENTAL CONDITIONS

国际海事组织（IMO）考虑制定一项涵盖带海锚救生艇的安全法规，因为大型浮动结构物或救生艇在波浪、风和水流等综合环境条件下倾覆时会发生严重死亡事件。实际上，这种规则的讨论是在对船舶倾覆机理没有深入了解的情况下进行的。IMO保证大型浮式结构物的安全，考虑到预留浮力的一些裕度或考虑到救生筏在真实的恶劣海况下的全尺寸试验。如果弄清楚这些浮体的倾覆机理，就有可能评估这些浮体在恶劣海况下的绝对安全性，并制定合理的浮体倾覆对策。本项目建立了浮体倾覆方程，并完成了考虑多向波浪作用的浮体时域行为计算机程序。线结构，如波浪、二阶波浪激励和分离流产生的非线性水动力。最后提出了带海锚救生筏安全性的评估方法，指出了风升力作为主导倾覆力的重要性。

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.