1. Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 e-mail:
2. SWANTEC Software and Engineering ApS, 373, Diplomvej Kongens, 2800 Kongens Lyngby, Denmark e-mail:
3. Ford Motor Company, Research and Advanced Engineering, Dearborn, MI 48121 e-mail: