Benchmark study of global linear wave loads on a container ship with forward speed

Results are presented of a benchmark study organised by the ISSC-ITTC Joint Committee on global linear wave loads on a container ship with forward speed. The aim of the study is the assessment of the uncertainty in linear transfer functions due to different seakeeping codes and consequences on long-term extreme vertical wave bending moments. Seven institutes participated in the benchmark, with fifteen seakeeping codes, representative of the linear seakeeping theories in use nowadays. Three general seakeeping methods are represented, namely strip theory, 3D frequency-domain method and 3D time-domain method. The benchmark ship is known as Flokstra's containership with well documented and accessible data of experimental results for motion and global wave loads. The comparative analysis is performed for heave and pitch motions and vertical wave bending moments at midship. Uncertainty measures employed are the frequency-independent model error and the coefficient of determination, representing bias and precision of the transfer functions respectively. Both uncertainty estimates are calculated for individual seakeeping codes with respect to the average of the corresponding method, and for each method average with respect to the experimental results. It is found that strip theory codes show the lowest uncertainty compared to the method average and that the agreement of the strip theory and experiments is better compared to other methods. Comparison of the present benchmark with a similar benchmark from 1996 doesn't show any improvement of the uncertainty. Reduction of the ship speed also doesn't have any apparent effect on the dispersion of results of individual codes. Uncertainty in the long-term predictions of vertical wave bending moment at midship caused by applications of different seakeeping codes is quantified, where large uncertainties are found. The possibility of reduction of these uncertainties using biases calculated in the present study is presented.