1. Member, ASCE
2. Assoc. Prof., Dept. of Mech. Engrg., Univ. of Southern California, Los Angeles, CA 90089.
3. Assoc. Prof., Dept. of Mech. Engrg., Wayne State Univ., Detroit, MI 48202.
4. Prof., Dept. of Aeronautical and Astronautical Engrg., Univ. of Illinois, Urbana, IL 61801; corresponding author.