1. Assistant Professor, Dept. of Aerospace Engineering, Cairo Univ., Giza 12613, Egypt; presently, Visiting Student, Dept. of Mechanical Engineering and Science, Edmund T. Pratt Jr. School of Engineering, Duke Univ., P.O. Box 90300, Hudson Hall, Durham, NC 27708-0300 (corresponding author).
2. Professor, Dept. of Aerospace Engineering, Cairo Univ., Giza 12613, Egypt.
3. Professor, ASU Sound and Vibration Laboratory, Dept. of Design and Production Engineering, Ain Shams Univ., Abbaseya, Cairo 11517, Egypt.