Effects of Ship Motion on Ship Maneuvering in Waves

Ship maneuvering performance is typically predicted in calm water conditions. This provides very valuable information at the initial ship design stage. However, since the ship always sails in waves, the maneuvering performance of the ship in seaway may be significantly different from calm water condition. Therefore, if the effect of waves and the corresponding motion responses can be included in mathematical model, the estimation will be much more reliable. In order to predict maneuvering performance of ship in waves, some simplified mathematical models have been developed by several researchers. McCreight(1986) developed a nonlinear maneuvering model in waves, which the hydrodynamic force related to wave-induced motion such as wave exciting forces, added mass and wave damping are evaluated in a body-fixed coordinate system by using the strip method. Fang et al.(2005) developed a mathematical model to calculate the hydrodynamic forces depending on encounter frequency in time domain simulation. However, these models did not consider the 2nd-order wave drift forces. Recently, the 2nd-order wave effect was considered more accurately by Skejic and Faltinsen(2008). In order to calculate the 2nd-order wave drift force, they proposed a two-time-scale model that separated low-frequency motion(maneuvering motion) and high-frequency motion(seakeeping motion). The above methods adopted 2D strip method to calculate wave induced motion. Recently, Lin(2006) estimated the ship maneuvering performance in waves using a 3D panel method. The nonlinear ship motion program, LAMP(Large Amplitude Motion Program), was extended to ship maneuvering problem. In the present study, maneuvering performance in waves is calculated using the time-domain nonlinear ship motion program WISH(Wave Induced load and SHip motion analysis) which applies a B-spline Rankine panel method. In this study, WISH has been extended to two main parts: the extensions to large lateral motions and the integration of seakeeping and maneuvering problems. To this end, the 2nd-order wave drift force is calculated using direct pressure integration method, and the MMG model is cooperated with the seakeeping model. The developed computer program is verified through the comparison with published experiment data, e.g. turning test of S-175 containership in calm water and in waves. Computational results show good correspondence with the experiment.