Of all the six degrees of freedom, the roll motion of a ship is the most poorly understood and displays complicated phenomena. Due to the low potential wave damping at the natural frequency, the effective analysis of ship roll dynamics comes down to the accurate estimation of the viscous roll damping. This paper provides overview of the importance of roll damping and an extensive literature review of the various viscous roll damping prediction methods applied by researchers over the years. The paper also discusses in detail the current state of the art estimation of viscous roll damping for ship shaped structures. A computer code is developed based on this method and its results are compared with experimental data to demonstrate the accuracy of the method. While some of the key references describing this method are not available in English, some others have been found to contain typographic errors. The objective of this paper is to provide a comprehensive summary of the state of the art method in one place for future reference.

Although linear ship motions theory is sufficiently accurate in predicting the motions of a ship/offshore platform in irregular seas, it cannot capture many of the nonlinear dynamic phenomena (e.g., parametric resonance) which might be very important in the design phase. In order to accurately simulate the motions of a structure, one has to resort to 6 degrees of freedom coupled nonlinear time-domain simulations. This paper presents the theoretical development of such a tool (called SIMDYN) which solves the nonlinear equations of motion while considering the large-amplitude rotations of the body. It also accounts for the nonlinearity of Froude-Krylov and hydrostatic forces. The validity of the developed tool is verified by comparing the predicted motions against the linear theory for small amplitude motions. The paper also shows an example of parametric roll simulation of a container ship to demonstrate the ability of the tool to capture nonlinear phenomena accurately. This tool is then applied to perform 30 3-h coupled simulations of a container ship in head seas, and the resultant time series from each simulation are analyzed to study the ergodicity of parametric roll in irregular longitudinal seas.

Traditional linear time-domain analysis is used widely for predicting the motions of floating structures. When it comes to a wave energy structure, which usually is subjected to larger relative (to their geometric dimensions) wave and motion amplitudes, the nonlinear effects become significant. This paper presents the development of an in-house blended time-domain program (SIMDYN). SIMDYN’s “blend” option improves the linear option by accounting for the nonlinearity of important external forces (e.g., Froude-Krylov). In addition, nonlinearity due to large body rotations (i.e., inertia forces) is addressed in motion predictions of wave energy structures. Forced motion analysis reveals the significance of these nonlinear effects. Finally, the model test correlations examine the simulation results from SIMDYN under the blended option, which has seldom been done for a wave energy structure. It turns out that the blended time-domain method has significant potential to improve the accuracy of motion predictions for a wave energy structure.

The increased interest in the design of energy efficient ships post IMO regulation on enforcing EEDI has encouraged researchers to reevaluate the numerical methods in predicting important hull design parameters. The prediction of added resistance and stability of ships in the rough sea environment dictates selection of ship hulls. A 3D panel method based on Green function is developed for vessel motion prediction. The effects of parametric instability are also investigated using the Volterra series approach to model the hydrostatic variation due to ship motions. The added resistance is calculated using the near field pressure integration method.

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