1. Ph.D. Student, Dept. of Ocean Engineering, Pukyong National Univ., 599-1 Daeyeon 3-dong, Nam-gu, Busan 608-737, Republic of Korea.
2. Professor, Dept. of Ocean Engineering, Pukyong National Univ., 599-1 Daeyeon 3-dong, Nam-gu, Busan 608-737, Republic of Korea (corresponding author).