1. Department of Mechanical Engineering, Shizuoka University, Jyohuku 3, Hamamatsu, Shizuoka 432, Japan
2. Department of Mechanical Engineering, Tsuyama National College of Technology, Tsuyama, Okayama 708, Japan
3. Department of Mechanical Engineering, Shizuoka University, Hamamatsu, Shizuoka, 432, Japan