1. 1R&D Center, Hankook Tire Co., Ltd., 23-1 Jang Dong, Yusung-Gu, Taejon 305-343, Korea
2. 2Department of Aeronautics and Astronautics Engineering, The University of Tokyo, 7-3-1 Honggo, Bunkyo-ku, Tokyo 113, Japan
3. 3Chuo University, 742-1 Higashi-Nakano, Hachiohji-shi, Tokyo 192-03, Japan