To investigate ship power characteristics and the difference between the towing model and self-propulsion model for ship motion response in waves, numerical simulations of ship self-propulsion performance in waves are carried out.

In this paper, the KCS ship model and KP505 propeller model are selected, and the unsteady Reynolds-averaged Navier-Stokes (URANS) method is used to carry out computational fluid dynamics (CFD) simulations of ship self-propulsion in waves. The in-house URANS solver HUST-Ship and in-house structured dynamic overset grid code HUST-Overset are combined to solve the motions of the self-propelled ship in waves, and the improved body-force model is selected as the propulsion model. Towing simulations for KCS with two-degrees-of-freedom (DOF) in waves and self-propulsion simulations with 3-DOFs under different wave conditions are carried out, and the differences between these methods are discussed in detail. Finally, the components and their specific proportions of added power during ship self-propulsion in waves are analyzed in detail using the logarithmic analysis method.

Regarding the added power of a self-propelled KCS in waves, the added resistance is responsible for 74%-77% while propulsive efficiency accounts for 23%-26%, that is, the added resistance occupy a larger proportion.

Reducing ship motion to decrease added resistance is the most effective approach to reducing added power.

Ship capsizing induced by pure loss of stability is an important issue for research on the second-generation intact stability criteria proposed by IMO.

A CFD solver based on the viscous theory is developed in combination with the dynamic overset approach and feedback controller for ship maneuver behavior, thereby simulating the course-keeping of a free-running ship with rudders and propellers in stern quartering waves. 6-DOFs motions are predicted for the ship under pure loss of stability with stability failure mode and capsizing assessment.

The results indicate that large amplitude roll motion occurs with the continuous loss of stability, and the extreme roll eventually leads to the ship capsizing. The yaw angle increases significantly with the variation in roll angle, which indicates that the rudder deflection is unable to control the ship's course effectively, resulting in the broaching phenomenon.

The results of this study demonstrate that the CFD approach can accurately simulate the stability failure mode and capsizing of a ship, providing references for research on the second-generation intact stability criteria, and technical support for the development of direct stability assessment under pure loss of stability.