Reduction of fuel oil consumption in sailing vessel has been a great interest even in the recent trend of low oil prices. The added resistance contributes the increase the fuel oil consumption of the vessel in actual sea environment. Therefore, the precise prediction of the added resistance is of great importance for developing highly energy efficient and low fuel consumption vessels. Ship experiences the added resistance by wind, current and waves in the sailing. In this paper, discussion is limited to waves, which generally gives high contribution as sea becomes harsh.
Potential flow codes for prediction of the add resistance in waves have been widely used due to its relatively fast computation time, but they have limitation to observe nonlinear interaction between waves and an advancing ship. Although CFD simulation is able to include such nonlinear interactions, the computation time is still quite demanding. For the efficient estimation on the added resistance, understanding the level of sophistication from different numerical methods is important to apply the proper methodology for accurate prediction.
In this paper, the numerical and experimental efforts to estimate the added resistance are made for an LNG carrier with twin skegs. Linear potential flow method and fully nonlinear RANS analysis are employed for numerical evaluation of the added resistance in waves. To validate the two different numerical methods, a self-propelled ship model test is additionally performed in regular wave conditions. The transfer functions of the added resistance from the three different approaches are compared, and noticeably different results are observed around short wave region. The discrepancy is then analyzed systematically by comparing the local waves at different position along the vessel hull. Comparison of the numerical and experimental results is summarized and discussions on the validity of each approach are then made.
Recently, the added resistance in waves is greatly concerned due to the growing demand of an optimized ship hull for energy saving efficiency in operational sea environment. A fundamental step to the optimization is to estimate the vessel's added resistance in an appropriate manner. Theoretical and experimental studies have been devoted to the added resistance and the efforts on improving the accuracy of estimation have been constantly made.