Since the early 21st century, driven by the integration of ship engineering and fluid mechanics, the research and development of large container ships and special vessel types have become key drivers of global trade, energy transportation, and port dredging. With the intelligent upgrading of canal networks, ship navigation efficiency has been significantly improved, while the requirements for navigation safety control have increased, necessitating more refined studies on hydrodynamic characteristics. Therefore, the research on various hydrodynamic coefficients is crucial, as they are directly related to the maneuvering performance of ships. Current research methods mainly include theoretical calculations, empirical formulas, model tests, and numerical simulations, among which model tests and numerical simulations are the two main approaches. Planar motion mechanism (PMM) tests provide core experimental data for studying the dynamic hydrodynamic characteristics of ships through six-degree-of-freedom motion simulations. Due to the high cost and long duration of model experiments, numerical simulation technology has emerged as a cost-effective and efficient tool for hydrodynamic coefficient research, thanks to turbulence model optimization and parallel computing.

The naoe-FOAM-SJTU solver, developed on the open-source platform OpenFOAM, is capable of handling dynamic overlapping grids. This solver integrates a self-developed multi-body six-degree-of-freedom motion solver module, enabling full simulation of various working conditions in ship PMM tests and facilitating comprehensive dynamic coupling analysis. For grid processing, the Suggar++ overlapping grid interpolation program is employed to generate domain connectivity information (DCI), ensuring accurate data transmission and stable coupling of flow field data between overlapping grids. In this study, the dynamic overlapping grid method is used in conjunction with the unsteady Reynolds-averaged Navier−Stokes (RANS) equations and SST k−ω turbulence model for numerical simulation. The SST k−ω model effectively combines the high accuracy of the k−ω model in the near-wall region with the robustness of the k−ε model in the far-field flow by closing the RANS equations. By introducing a mixing function and constraining the turbulent eddy viscosity, the model significantly improves the prediction accuracy of complex flows, especially separated flows. Based on the aforementioned numerical methods, a systematic hydrodynamic numerical simulation and analysis of the pure sway motion of the KVLCC1 ship model were carried out in both deep and shallow water environments with different water depth-to-draft ratios.

Comparisons with experimental results show that the errors in sway force amplitude, yaw moment amplitude, and phase angle relative to the experimental values are mostly around 5%, verifying the feasibility of using the overlapping grid method for ship hydrodynamic calculations. This result further confirms that the selected calculation model can accurately reflect actual conditions, ensuring the effectiveness and credibility of numerical simulations in engineering applications. In both deep and shallow waters, the hydrodynamic coefficients in shallow water are significantly larger than those in deep water, which is closely related to the shallow water effect. This effect can lead to deteriorated maneuverability of ships in shallow water, especially during large-angle steering, where the maneuvering performance may be seriously affected. Additionally, the sway force amplitude and yaw moment amplitude are found to have a linear relationship with the dimensionless sway velocity amplitude v′. The shallow water effect significantly increases the flow velocity on both sides of the hull and the hull bottom. In areas with increased flow velocity gradients, the regions with higher flow velocity are mainly concentrated at the bow and stern in deep water, while they extend across the entire hull bottom in shallow water. In deep water, the velocity distribution behind the stern is more stable compared to that in shallow water. Regarding the wake, under deep water conditions, the wake is relatively stable, fully developed, and has a more regular shape than that under shallow water conditions. In shallow water, the low-velocity and low-pressure areas in the wake are more pronounced than those in deep water, which is caused by the insufficient development of the wake due to limited vertical space (z-direction). Furthermore, the forebody bilge vortex is less developed in shallow water due to restricted vertical space.

This research provides valuable references for ship maneuverability analysis.

To improve hull optimization design efficiency and obtain better optimization results, different fidelity data is organically integrated and a multi-fidelity deep neural network is applied.

A multi-fidelity deep neural network is constructed based on the idea of multi-source data fusion and transfer learning. By fusing a large amount of low-fidelity data with a small amount of high-fidelity data, the linear and nonlinear terms between the high-fidelity data are constructed to obtain a high-fidelity surrogate model. Based on this method, the optimization design of the resistance of a DTMB 5415 ship is carried out. The potential flow and viscous flow are used to evaluate the resistance of the sample points respectively. The potential flow calculation results are used as low-fidelity data, while the viscous flow calculation results are used as high-fidelity data. A multi-fidelity deep neural network surrogate model is then constructed. The optimal solution is obtained by genetic algorithm and compared with the optimal solution of the Kriging model constructed by high-fidelity data.

Based on the multi-fidelity deep neural network method, the resistance of DTMB 5415 is reduced by 6.73%. Based on the Kriging model, the resistance of DTMB 5415 is reduced by 5.59%.

The multi-fidelity deep neural network surrogate model can take into account both efficiency and accuracy, which can be used for optimization. The optimized hull form obtained by it has a more significant resistance optimization effect.

As tip vortex cavitation (TVC) causes noise radiation and vibration, it is necessary to understand how to predict and control its development, and understand its mechanism in order to suppress it, especially in the field of ship propellers and other rotating machinery.

Focusing on an elliptical hydrofoil with an NACA 0012 cross-section, this study uses the Improved Delayed Detached Eddy Simulation (IDDES) turbulence modeling method and Schnerr-Sauer cavitation model to simulate TVC on the hydrofoil and analyze its behavioral characteristics under wet flow and cavitation flow conditions. After that, two active water injection methods, side injection and top injection, are introduced into the simulation to reduce and suppress cavitation inception respectively.

Taking the cavity volume of the tip vortex as the criterion for cavitation suppression, compared with the condition without water injection, top injection can inhibit cavitation by 8.09%. Moreover, under the condition of side injection, the effect of the injecting flow on the cavitation is more obvious, reaching 10.47%. The results show that both top and side injection can effectively suppress TVC.

Top injection can change the flow direction and speed of the tip vortex incident flow, and increase the dissipation term of the turbulent kinetic energy; while in side injection, the energy it carries acts directly on the vortex structure of the hydrofoil, destroying the vortex and greatly suppressing the generation of cavitation.

Poiseuille flow widely exists in the industry, but the stability and reliability of the moving particle semi-implicit (MPS) method in the simulation of wall shear flow such as Poiseuille flow need to be verified.

The meshless solver MLParticle-SJTU, which was developed independently based on the MPS method, is used to simulate Poiseuille flow in 2D pipes under different Reynolds numbers by establishing the inflow boundary and no-slip wall boundary, and the fluid is an incompressible Newtonian fluid. The numerical simulation results and theoretical results are then compared to verify the accuracy of the former.

The results show that the velocity profile of Poiseuille flow is parabolic when the flow is fully developed, and the error of the numerical simulation results is within 5% compared with the theoretical results under different Reynolds numbers.

This study shows that the MPS method is effective and reliable for simulating 2D Poiseuille flow under the boundary conditions proposed in this paper.

In order to forecast a ship's maneuverability more realistically, it is necessary to conduct the direct simulation of the full-scale ship's maneuver.

In this paper, based on overset grid technology, calculations of the full-scale ship towing, supporting propeller open water and full-scale ship self-propulsion are first produced, and the calculations are then compared with the experimental results. On this basis, numerical simulations of the full-scale ship's 10/10 standard zigzag maneuvers are carried out to analyze changes in the ship's motion, hydrodynamics, flow field and vortex structure.

The self-propulsion results show that the numerical method used in this paper is reliable. The torque coefficient decreases due to the propeller scale effect. When maneuvering, the ship's motion is more intense. Due to the interference of the ship-rudder system, the post-propeller vortex structure is more complicated and produces a certain angle of offset with the change in drift angle.

The ship's motion, hydrodynamic characteristics and flow field information can be accurately obtained using this numerical method to simulate full-scale ship maneuvers, it can be used as an effective pre-evaluation tool and provide references for ship design.

The viv-FOAM-SJTU solver is used to carry out the numerical simulation of the vortex induced vibrations of a riser under different top oscillation excitation amplitudes.

The flow field is computed by the strip theory and Reynolds-averaged Navier-Stokes (RANS) method, while the Bernoulli-Euler bending beam theory and finite element method are employed to model the structure of the riser.

The simulation results show that the cross-flow vibrations transform from multi-mode to single mode with the decrease in oscillation amplitude. At the same time, the inline vibrations maintain single mode, but the amplitude of the mode vibration decreases.

With the variation in top oscillation excitation amplitudes, the washing out of the riser by shed vortices affects the characteristics of vortex induced vibrations.

In the design stage of a luxury cruise ship, in order to save costs, it is necessary to use the computational fluid dynamics (CFD) method to predict the seakeeping performance of the cruise ship under design.

The research object of this paper is a large luxury cruise ship. The self-developed ship hydrodynamics CFD solver naoe-FOAM-SJTU is used to simulate the seakeeping performance of the luxury cruise ship at model scale. The seakeeping simulation adopts the speed entrance input wave-making method, and predicts and summarizes the cruise movement under different wave heights and downwards.

The evaluation finds that the designed cruise ship model basically meets the requirements of ship comfort at maximum speed and wave heights of 0.062 5, 0.1 and 0.15 m, and meets the requirements of ship safety at the design speed, wave height of 0.225 m and heading sea conditions.

Under the calculated working conditions, this cruise ship design conforms to the safety and comfort standards in the seakeeping evaluation standards of luxury cruise ships.

This study seeks to optimize the total resistance and seakeeping performance of ships sailing in waves by adding appendages and changing their size.

First, numerical calculations are performed on a KCS ship with two anti-pitching fins and a stern flap, and both kinds of appendage separately, to study the effects of the appendages on the hull. Second, thirty KCS ships with deformed appendages are obtained by changing the width of the anti-pitch fins and the length of the stern flap. The in-house viscous flow solver naoe-FOAM-SJTU is used for the calculations. Third, a Kriging surrogate model is established and applied to a multi-objective genetic algorithm to obtain the Pareto front of the hull with optimal appendages. Three KCS ships with optimal appendages are selected from the Pareto front for further analysis.

By adding appendages to a KCS ship, the pitch magnitude and average total resistance in an encounter period are reduced by about 12.7% and 12.5% respectively.

The resistance and pitch magnitude of a KCS ship in head waves can be optimized by adding appendages such as anti-pitch fins and stern flaps, and changing their principal dimensions.