where zn is the heave nth order amplitude, qn is the pitch nth
order amplitude, and gzn and gqn are the phase differences.
The amplitudes of the ship's motions is obtained by the FFT
analysis of the computed time history of ship's motion where the first harmonic is taken as the motion amplitude. For this unsteady analysis, the computation time is chosen as 40 s. In order to diminish the effect of sampling error on the numerical added resistance and ship motion in wave, the data in the final 10 s is used for the FFT study. Numerical and experimental FFTs of heave and pitch motions are given in Fig. 11. Nu- merical results in wave are compared with experimental data in Table 5.
The experimental results can be obtained from G2010 (2010) and Guo et al. (2012). As can be seen from Table 5, the comparisons show that numerical calculations well predict the heave and pitch motions of KVLCC2 model. FFTs of z and q mostly appearance robust response at the encounter fre- quency. The wavelength in condition C3 is very large (l/ LPP ¼ 1.600) and thus displays a very linear behavior.
4.3. Added resistance
Potential flow approach is frequently used for added resistance problems. However, for some seakeeping simula- tions, such as, green water calculations, slamming impact loading, breaking waves, etc., potential flow cannot handle the problem properly. In order to overcome the restrictions of strip theory, efforts to extend numerical methods for viscous flows