1. Dynamics and Vibrations Group, Numerical Methods in Mechanical Engineering, Technische Universität Darmstadt, Dolivostr. 15, Darmstadt 64293, Germany
2. College of Aerospace and Civil Engineering, Harbin Engineering University, Harbin 150001, China e-mail:
3. Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino 10129, Italy