1. School of Civil and Hydraulic Engineering, Hefei University of Technology, Hefei 230009, China
2. School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China
3. LAETA/INEGI, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
4. School of Mathematics, Anhui University, Hefei 230601, China