To assess ship maneuverability in waves, computations of a ship with heave, roll and pitch motions in oblique wave are presented. The wave drift forces, heave and pitch motions are investigated numerically. The computations are based on volume of fluid (VOF) and overset mesh methods, discretized by finite volume method (FVM). An open source library, wave2Foam, is used to generate desired wave conditions. Seven wave conditions with a wide range of incident angle are considered. The wavelength is in the range of short waves and the results show strong nonlinear features, especially for beam wave and following waves, where the phenomenon of wave breaking on port side and stern is observed. The comparison of wave drift forces between the present computational results and measurements shows good agreement.
The background of the presented research is the implementation of the Energy Efficiency Design Index (EEDI), by the IMO in January 2013 and the associated requirement for each new-built vessel to meet reference lines for vessel emissions. To meet the EEDI requirements, some ship designers/builders choose to lower the installed power and ship' s speed instead of putting effort to optimize ship' s speed-powering performance. It leads to raise concerns regarding the sufficiency of propulsion power and steering devices to maintain maneuverability of ships in adverse conditions. It is evident that when a ship is operating in adverse weather conditions, wave drift forces and moments will act on ship and change its course. Therefore, it is necessary to develop suitable tools to effectively evaluate wave drift forces and moments and to enable people assess ship maneuverability in waves.
To address these issues, extensive experimental and numerical investigations were performed within the European funded Project SHOPERA. In this project, one of the tested ship selected for benchmark and validation was a post Panamax 14000 TEU containership, the Duisburg Test Case (DTC). To gain the drift forces of DTC, systematical test cases consisting of different drift angles were conducted in the European maritime experimental research institutes MARINTEK. Basing on their experimental data, we use CFD solver, naoe-FOAM-SJTU (Shen and Wan, 2011; Shen et al., 2012; Shen and Wan, 2012; Cao et al., 2013), to perform simulations on DTC and calculate the drift forces in the expectation of obtaining some details of DTC's hydrodynamic characteristics.
There are many previous studies focusing on wave drift forces, most of which are using the potential theory. Grue and Palm (1993) discussed the effect of the steady second-order velocities on the drift forces and moments acting on marine structure in waves and a (small) current. Following that, Hermans (1999) presented numerical results for two classes of tankers, namely for a VLCC and a LNG-carrier, and a semisubmersible and compared with experimental data obtained at the Maritime Research Institute in the Netherlands (MARIN). Tanizawa et al. (2000) applied a linear and a fully nonlinear numerical wave tanks (NWTs) to study wave drift force acts on a two-dimensional Lewis form body in finite depth wave flume.
However, the conventional potential methods still have limitations when handling strong nonlinear problems. Owing to the rapid development of computer power, computational fluid dynamics (CFD) has experienced unprecedented developments in recent decades. Since reliable multiphase models and turbulence models are developed, CFD can handle more nonlinear problems and obtain more accurate results.