1. Professor, Division of Ocean Development Engineering, Korea Maritime Univ., Busan 606-791, Korea.
2. Graduate Student, Research Institute for Applied Mechanics, Kyushu Univ., 87 Kasuga 816-8580, Japan.
3. Assistant Professor, Research Institute for Applied Mechanics, Kyushu Univ., 87 Kasuga 816-8580, Japan.
4. Professor, Research Institute for Applied Mechanics, Kyushu Univ., 87 Kasuga 816-8580, Japan.