This study presents comparison of the numerical results of added resistance on ships in waves between the Neumann-Kelvin and doublebody free-surface linearization approaches. In the present study, the time-domain formulation is considered and the corresponding equations of added resistance are derived. As a method of solution, a higher-order Rankine panel method is used, and the added resistance is evaluated directly by integrating the second-order pressure on the body surface. Computational results are validated by comparing with experimental data and other computational results on Wigley hull models, Series 60 hull, and S175 containership, and reasonable agreements are observed for all the models. Comparisons between the numerical results based on two free-surface linearization schemes are summarized in the paper, and the pros and cons of each approach are discussed. The study is extended to the analysis of added resistance in irregular waves, and the proper criteria for time window and number of simulations are observed for irregular sea.
An accurate prediction of added resistance is important in a ship design of propulsion power, therefore the added resistance problem has been widely studied for long time. Experimentally, added resistances on the Series 60 hull and the Wigley hull have been measured by Gerritsma and Beukelman (1972), Storm-Tejsen et al. (1973) and Journee (1992), respectively. Two major analytical approaches can be used to analyze the added resistance problem. One is a far-field method which is based on the momentum-conservation theory proposed by Maruo (1960). This approach is simple and powerful because there is no need to solve a complete boundary value problem to obtain the body pressure, thus the far-field method has been widely used to estimate added resistances in real applications. However, this method has a limitation in evaluating a control surface, and it is not easy to apply for oblique sea case.