The application of various free-flooding ships is increasing year by year, and the characteristic of these ships is the presence of both water tank sloshing and connectivity between internal and external seawater. In order to study this specific phenomenon, a numerical simulation is conducted.

Using a CFD commercial software platform, a 3D model of a free-flooding ship section with openings on the port and starboard sides is established. The forced rolling motions under different roll periods and amplitudes are simulated in a viscous numerical water tank. Then, the relationship between the mass flow rate at the openings and the applied working conditions is studied.

The results show that if the roll period is bigger, the flow amplitude ratio will also be bigger and the time difference between the mass flow and the ship's rolling velocity will be smaller.

The adopted method can accurately simulate the water exchange, and this water exchange will exhibit strong regularity. Based on this, further studies can be conducted on the hydrodynamic performance of free-flooding ships.

In order to rapidly forecast added wave resistance in the ship design stage, this paper proposes a neural network based on point cloud feature extraction.

Taking the Series 60 as an example, the corresponding added wave resistance prediction model is set up and compared with the traditional model based on the principal design parameters. By referring to S60 ship tests, the characteristics of the point cloud prediction model in terms of accuracy and stability are discussed, as well as the method of pre-training and optimizing the model using ship calm-water resistance data.

The prediction results indicate that the proposed model can perform well in all five S60 ships, with the coefficient of determination R² ranging from 0.74 to 0.90, while the traditional model based on the design parameters fails to make the correct prediction in some case.

This study provides new insights and a new approach to predicting added resistance in ship design, and may help to optimize ship forms by fully considering the impact of added wave resistance in the design phase.

To simulate the complex nonlinear interactions between the free surface and instantaneous wetted hull surface during ship navigation, an automatic mesh generation method is proposed.

The method takes a whole-hull triangular mesh file as the input and automatically generates meshes for the instantaneously transforming free surface and wetted hull surface. It is able to handle arbitrary hullforms with complex bow and stern geometries while exhibiting strong robustness. Simulations of waves generated by a KCS hull at various speeds are then conducted using the proposed method.

The predicted ship-side wave profiles, wave patterns around the hull, and wave-making resistance show good agreement with the experimental results. Moreover, at higher speeds, the simulated wave surface at the KCS stern consistently stays below the transom, exhibiting a dry transom characteristic.

The results demonstrate that the proposed method can accurately model nonlinear ship waves and has the potential to simulate the flow fields around transom-stern ships.

This study seeks to address the low-frequency limitations in the computation of hydrodynamics for slender ships using strip theory, and develops an efficient method for calculating hydrodynamics over a wider frequency range for slender ships using a simplified approach.

Based on the unified theory of strip theory and ordinary slender body theory, the added mass and damping coefficients of a prolate spheroid, slender, modified Wigley model and S60 ship are calculated programmatically. A comparison is made between the calculated results using the unified theory and experimental data, as well as results obtained from strip theory, 3D translating and pulsating source Green's function method and other methods. The computational characteristics and advantages of the unified theory are then analyzed.

The results indicate that the unified theory based on 2D sections produces results under zero-speed conditions that are consistent with those obtained by the 3D panel method. For conditions involving ship speed, the calculated results exhibit consistent variations with those obtained from the 3D translating and pulsating source Green's function method.

The proposed unified theory is capable of reflecting 3D effects in the low-frequency region, which gives it greater efficiency and simplicity compared to 3D methods, and thus significant practical value.

Aiming at the nonlinearity of trimaran rolling, a system identification modeling method combining CFD and support vector regression (SVR) is proposed.

Based on the STAR-CCM+ platform, numerical simulations of forced rolling motion of the trimarans with different lateral layouts are performed. Then the SVR method is used to identify the parameters of the hydrodynamic moment history curve and calculate the additional mass and damping coefficient of the hull at different frequencies.

The results show that the damping coefficient of the trimaran shows strong frequency dependence; the nonlinear characteristics of the damping are profound at low frequencies, and the damping component of the bilge keel accounts for a large proportion.

Compared with potential theory, the proposed SVR method can accurately capture the nonlinear characteristics of the trimaran's rolling motion, and better account for the flow interactions between hulls.