1. Division of Ocean Systems Engineering, Korea Advanced Institute of Science and Technology, 373-1 Gusong-dong, Yuseong-gu, Daejeon 305-701, South Korea
2. Department of Mechanical Engineering, Dong-A University, 37, Nakdong-daero 550beon-Gil, Saha-gu, Busan 604-714, South Korea
3. Department of Precision Mechanical Engineering, Kyungpook National University, 386 Gajang-dong, Sangju, Gyeongsangbuk-do 742-711, South Korea e-mail: