Trimarans have complex motion state in oblique stern wave conditions caused by the coupled motion of roll and pitch, because of the small encounter frequency and hydrodynamic interference between main hull and side hulls. In this paper, pitch and rolling motion responses of trimaran in oblique stern waves are predicted by the open source CFD code OpenFOAM. The numerical method is validated by comparing with experimental research and grid convergency research. The numerical results are analyzed to research the coupled motion characteristics and motion states. The results show that pitch motion of trimaran is smaller at short wave condition, but the rolling motion shows nonlinear characteristics; large wave steepness increases both pitch and roll, but the effects are totally linearity; low forward speed aggravates the influence of wave steepness on rolling motion, but has no effects on pitch motion.
Trimaran has been developed rapidly in recent years. Academic research, including numerical research and experimental research, and full scale industrial both have rapid development. Trimarans have many advantages (Davis, M.R.and Holloway,D. S.,2007; Brizzolara, S. et al., 2003; Bertorello, C. et al., 2001), such as high design speed, high effective power and excellent stability, while some disadvantages still need to be studied.
It is well known that the position of side hulls affects hydrodynamic of the trimaran obviously (Ghadimi, P. et al., 2019; Fang, M. C. and Too, G. Y.,2006). In order to get a better performance, side hulls usually located near the stern of mid-hull. With this configuration, trimaran has balanced performance of resistance, seakeeping and maneuvering. But the interference of main hull and side hulls are really grievous when the vessel sails in waves especially following waves and oblique stern waves. The interference would cause severe nonlinear motion and incentive, which would cause the unstable motion of trimaran.
