1. a School of Mechanical Engineering, Pusan National University; 30 Jangjeon-dong, Gumjeong-gu, Busan 609-735, South Korea;, Email: kshong@pusan.ac.kr
2. b School of Mechanical Engineering, Pusan National University; 30 Jangjeon-dong, Gumjeong-gu, Busan 609-735, South Korea
3. c Department of Mechanical Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, South Korea