1. College of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001, China
2. Department of Differential Equations, Altai State University, 656049 Barnaul, Russia
3. Lavrentyev Institute of Hydrodynamics, Siberian Branch of the Russian Academy of Sciences (SB RAS), 630090 Novosibirsk, Russia
4. School of Mathematics, University of East Anglia, Norwich NR4 7TJ, UK