In this paper, the second-order perturbation method in frequency domain is used to calculate RAO and spectra of motion and mooring line tension of a turret-moored tanker in ballast condition. The calculated results are compared with corresponding experiment results. In the experiment the wave heading is 180 degrees, and the wave spectra is the P-M spectrum and white noise spectrum. In the theoretical calculations, the damping coefficient of slow oscillation of the tanker is determined on the basis of the damping obtained from a test of irregular waves where the mooring system is replaced by a nonlinear spring with nonlinear stiffness similar to that of the mooring system. From the comparison between theoretical calculations and experiment al results, it can be found that the theoretical results obtained by the second-order perturbation method in frequency domain are in good agreement with the experimental results, indicating that the damping coefficient of slow oscillation of the tanker required in frequency domain calculation can be determined by reference to the damping coefficient of the tanker moored by a spring system in irregular waves, and the second-order perturbation method can be used to analyze the dynamic response of a turret-moored tanker.
