1. Department of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu 139-743, South Korea e-mail:
2. Division of Mechanical and Automotive Engineering, Kongju National University, 1223-24, Cheonan-daero, Seobuk-gu, Cheonan-si 330-710, Chungcheongnam-do, South Korea e-mail: