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The advanced numerical methods with new model and scheme, to reduce the requirements of the computation times and computer resources for seakeeping predictions, are urgent according to the International Towing Tank Conference seakeeping committee. In the present study, different propulsion models are used to implement the seakeeping performance simulations of a self-propelled surface ship sailing in waves. Both the accuracy and the computational cost are investigated. Four different propulsion models for self-propelled surface ship simulation including the discretized propeller model, the descriptive body-force method, the Osaka University method and the modified Osaka University method were studied. Uncertainty analyses are conducted separately for hull, propeller in calm water and ship motions in waves. Numerical simulations in calm water and waves are carried out to obtain the ship attitudes, resistance, motion responses and added resistance. Self-propulsion simulations in calm water and waves are performed to obtain the propeller rotation speed, the ship motions and the speed loss. Four wavelengths ( λ / L pp = 0.65 , 0.85 , 1.15 , 1.95 ) of regular head waves with a wave steepness of 1/60 are considered according to the benchmark case of the Tokyo 2015 Computational Fluid Dynamics Workshop. The self-propulsion simulation results of the thrust, torque, ship motions and speed loss using different propulsion models have been compared to each other. It can be found that all the differences of speed loss are less than 2% and these of heave and pitch amplitudes are less than 6.13%. The modified Osaka University method, which provides numerical results closest to those of the discretized propeller model, is an alternative method for ship self-propulsion simulations in waves. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations of the parametric roll of a ship coupled with liquid sloshing were performed. A model-scale ONR Tumblehome was used for the simulation, and the ship was equipped with a partially filled liquid tank. An in-house unsteady Reynolds-averaged Navier–Stokes solver was applied to the numerical simulation of the coupling effect between the sloshing and parametric roll of the ship in regular head waves. First, a validation study of the computational fluid dynamics (CFD) solver was conducted. Comparisons between the CFD and experimental results showed good agreement. Systematic grid and time-step convergence studies were performed to estimate the numerical uncertainty. The effect of liquid sloshing on the parametric roll of a ship was then investigated numerically with different liquid levels and different ship forward speeds. The results demonstrated that water sloshing could significantly decrease the natural roll frequency of the ship model, which led to a lower speed range where the parametric roll occurred compared with the model without sloshing. The phase difference between the total moment and sloshing-induced moment was close to 180°, resulting in a reduction of the parametric roll amplitude. Sloshing had slight effects on the amplitudes of the heave and pitch motions. • The coupling effect between the sloshing and parametric roll of the ONR Tumblehome was investigated. • Numerical simulations were conducted by an unsteady RANS solver with dynamic overset grid method. • The wave- and sloshing-induced loads were analyzed under the parametric roll condition. [ABSTRACT FROM AUTHOR]

Ship capsizing in stern quartering wave is very complicate with a strong correlation to the stability failure modes proposed in second-generation intact stability criteria. It is of great importance to shed some light on this complex phenomenon. In this study, the capsizing behavior of a free-running ONR Tumblehome model in stern quartering seas is investigated by an unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with dynamic overset grid approach. Validation study of the URANS solver is performed for the prediction of extreme roll motion of the ship. The comparisons show satisfactory agreement, with an average difference less than 3% between the simulation and experimental results. The correlation between the occurrence of stability failure modes (surf-riding, pure loss of stability, and broaching) and ship capsizing is then assessed under different ship speed and heading angle conditions. It is concluded that the capsizing occurs as the free-running ship sailing with a high speed, which is caused by the interaction between the broaching and severe stability loss. In addition, influenced by the wave-induced moment, both the pure loss of stability and surf-riding modes may cause the broaching, indicating the similar occurring condition and strong relation between these stability failure modes. • Ship capsizing in stern quartering wave are directly simulated by an unsteady RANS solver. • Pure loss of stability, surf-riding, and broaching are observed for the ship in stern quartering waves. • Both the pure loss of stability and surf-riding may cause the broaching, closely coupled with ship capsizing. • Wave-induced yaw moment with a small heading angle is not enough to cause the broaching. [ABSTRACT FROM AUTHOR]

With the advances in available brute-force computing power, parallel computations (overset grid technology and meta-modeling) will eventually open a path to the widespread application of full-scale computations. This study presents a computational fluid dynamics (CFD) prediction of a full-scale ship parametric roll in a regular head wave. An in-house unsteady Reynolds-averaged Navier–Stokes (URANS) CFD code was used for the simulations. The ONR Tumblehome surface combatant was selected as the research object, and the full-scale ship was studied under the same conditions as the model tests. Comparisons between the CFD results and model test results from the reference show good agreement and validate that the code could capture the details of parametric roll phenomenon in head waves. The full-scale predictions were compared with the model-scale results to assess the scale effect of the parametric roll. The induced force and moment acting on the hull under the parametric roll were analyzed. Simulations for ships with bilge keels were also performed at model- and full-scale to evaluate the effect of bilge keels. Numerical results demonstrate that the in-house URANS code could be used to predict the parametric roll characteristics for a full-scale ship at the design stage in the future. [ABSTRACT FROM AUTHOR]