This study considers the prediction of speed loss of ship in waves by using time-domain seakeeping-maneuvering coupled approach. To this end, the time-domain seakeeping analysis based on the three dimensional Rankine panel method is coupled with the modular type 4- DOF maneuvering equation. In the coupling procedure, the seakeeping performances, which are dependent on direction and encounter frequency of wave, and the maneuvering motions, which are influenced by wave-induced drift force, are directly interacted with each other in time domain. Especially, the drift force, which is the main cause of speed loss in waves, is calculated by the near-field method, namely, the direct pressure integration method. In order to validate the developed coupling method, the computed drift force and turning trajectory with the presence of an incident wave are compared with existing experimental data. Then, by implementing the trajectory tracking method based on rudder control, the free-running simulation for ship keeping a certain course in wind and wave is performed. The effects of environmental loads on speed loss are investigated by conducting the simulations for various environmental conditions including irregular seas and winds in different directions. Through this process, it is confirmed that the present free-running simulation can be used for evaluation of ship operation performances such as operation efficiency and course keeping.
In recent years, the importance of ship efficiency and safety in the real sea state has been growing, and related regulations have been actively established. In particular, the Marine Environmental Protection Committee (MEPC), one of the specialized committees of the International Maritime Organization (IMO) introduced the regulation related with energy efficiency to reduce the amount of greenhouse gas emitted by ship. According to the regulation, the calculation of the Energy Efficiency Design Index (EEDI) becomes mandatory for ships sailing internationally. The EEDI includes prediction of the weather factor (fw), which means the speed loss of ship in actual operation conditions. Therefore, in order to predict the weather factor, accurate computations of the added resistance induced by environmental loads such as wind and wave are required as well as the calm-water resistance.