1. Visiting Scholar, Dept. of Mechanical Engineering, Univ. of Akron, Akron, OH 44325; formerly, Graduate Student, School of Aeronautics, Northwestern Polytechnical Univ., Xi'an, Shaanxi 710072, PRC.
2. Professor, School of Aeronautics, Northwestern Polytechnical Univ., Xi’an, Shaanxi 710072, PRC.
3. Graduate Student, Dept. of Mechanical Engineering, Univ. of Akron, Akron, OH 44325.
4. Graduate Student, Dept. of Civil Engineering, Univ. of Akron, Akron, OH 44325.
5. Professor, Dept. of Mechanical Engineering, Univ. of Akron, Akron, OH 44325 (corresponding author).