1. Professor, Dept. of Applied Mechanics and Aerospace Engineering, Waseda Univ., 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan (corresponding author).
2. Student, Dept. of Applied Mechanics and Aerospace Engineering, Waseda Univ., 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan.