| dc.description.abstract | Added resistance in waves is important for ship powering performance, since ships are travelling most of the time in waves, not in calm water. With increasing focus on fuel consumption and greenhouse gas emissions, there is increasing focus on optimizing the resistance and fuel consumption of ships. Traditionally, ships have been optimized for operation in calm water, since the trial voyage is performed in calm water, and the optimization for operation in waves is much more difficult. Nowadays, it is realized that the ship needs to be optimized for the operation for which it is designed. This means that most merchant ships shall be optimized for operation in waves – typically waves that are fairly short relative to the length of the ship. In order to optimize the ship hull geometry for operation in waves, efficient and reliable methods for determination of the added resistance due to waves are required. Although significant effort has been devoted to this question over the years, there is still a lack of such methods. This thesis discusses the nature of the added resistance, and investigates several different methods for determining the added resistance: model test, strip theory methods, a boundary element method and advanced numerical methods based on Reynolds Averaged Navier- Stokes equations (RANS).
A series of experiments on a segmented model of the KVLCC, with three different bow shapes, were performed in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Tests were carried out in different short head waves at different forward speeds. The resistances of the whole hull, fore segment and aft segment were measured. Also the frictional resistance of the mid segment was measured. The difficulties of accurate measurement of added resistance in short waves are outlined. A novel method for eliminating low-frequency noise from the measured resistance was proposed. It was found that in short waves, the added resistance is concentrated in the bow. Thus, the optimization of bow shape could reduce the added resistance effectively, and the comparison of the added resistance from different bows show that the slender bow could reduce the added resistance. There is almost no added frictional resistance on the mid segment in very short waves, indicating that the currently common assumption of neglecting added frictional resistance due to waves is reasonable. Our investigation did not give results for added frictional resistance in long waves. Parts of the dataset generated from the tests with the original bow shape of KVLCC2 have been applied as benchmark data in the workshop Gothenburg 2010 on numerical ship hydrodynamics.
The added resistance from theoretical methods based on strip theory is compared with the experimental results. It is found that the ‘radiated energy method’ of Gerritsma and Beukelman predicts the added resistance in long waves quite well, but underestimate the added resistance in short waves. The ‘pressure integration method’ proposed by Faltinsen is found to be very sensitive to the ship hull discretization and doesn’t give good results for the studied cases. For short waves, when ship motions are negligible (λ | nb_NO |
