1. Department of Mechanical Engineering, Chonnam National University, Gwangju 500-757, Korea
2. Department of Mechanical Engineering, Chonnam National University, Gwangju 500-757, Korea,
3. College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou 325-035, People's Republic of China, Department of Mechanical Engineering, Chonnam National University, Gwangju 500-757, Korea