1. Department of Automotive Eng., Woosuk University, Wanju-kun, Jeonbuk, Korea
2. Dept. of Naval Architecture and Ocean Eng., Chosun University, Gwangju, Korea
3. Dept. of Mechanical Design Eng., Chosun University, Gwangju, Korea
4. Center for Nondestructive Evaluation, Iowa State University, Ames, Iowa, USA