When two waves in different directions meet due to different weather patterns, a cross wave pattern will be generated, which will finally result in the spread of square waves on the sea surface. The emergence of square waves will threaten the navigation performance of a ship and may lead to capsizing of a ship in severe cases. In this paper, the numerical square wave tank is developed by using the in-house CFD software HUST-Ship. In the process of simulation, by means of solving the unsteady RANS equation of incompressible fluid, the analytical solution of the corresponding regular wave is generated at the inlet boundary, and the free surface is captured by level-set method. Square wave is generated by superimposing two vertical regular waves with the same wave length, wave height and phase. Through analyzing the CFD model of square wave, the uncertainty analysis of wave height and length are performed. The verification and validation procedures of grid and time-step are performed to ensure the credibility of simulation results. Moreover, a detecting point is set at the origin to get the time history curve of the wave height. The linear solution and second-order Stokes solution of waves are used to fit the wave height time-history curve respectively.

Numerically simulating a ship with six-degrees-of-freedom response motions of an unsteady maneuver in a wave environment is very important in seakeeping characteristics of ship design. This paper presents the simulation studies of the turning motion in regular waves of the ONRT model. Numerical simulations were performed using viscous CFD code HUST-Ship to solve the RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations and dynamic overset grids designed for ship hydrodynamics. RANS equations are solved by the finite difference method (FDM) and PISO arithmetic. The level-set method is used to simulate the free surface flow. Before the turning circle simulation, a V&V study is conducted for the total towed resistance. The real propeller was replaced by a description body force method in the process of turning motion. The constant rate of the revolution was applied throughout the simulation. The rotation of the propeller corresponds to the self-propulsion point of the model speed. The control of rudders was controlled by the following autopilot. The maximum rudder rate was assigned to 35.0 [deg/s]. The ship was released when a wave crest is passing the midship. The study focused on the parameters of the trajectories for turning circle, roll, pitch, velocity, etc, it is helpful to judge the influence of the wave on the turning motion. The simulation results match well with test data from IIHR.

The dangerous situation caused by the breakage of the ship will pose a serious threat to crew and ship safety. If the ship’s liquid cargo or fuel leaks, it will cause serious damage to the marine environment. If damage occurs accompanied by roll and other motions, it may cause more dangerous consequences. It is an important issue to study the damaged ship in time-domain. In this paper, the motions of the damaged DTMB 5512 in calm water and regular beam waves are studied numerically. The ship motions are analyzed through CFD methods, which are acknowledged as a reliable approach to simulate and analyze these complex physical phenomena. An in-house CFD (computational fluid dynamics) code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) is used for solving RANS equations coupled with six degrees of freedom (6DOF) solid body motion equations. RANS equations discretized by finite difference method and solved by PISO algorithm. Level set was used for free surface simulation. The dynamic behavior of model was observed in both intact and damaged condition. The heave, roll and pitch amplitudes of the damaged ship were studied in calm water and beam wave of three wavelengths.

Design requirements for submarines regarding resistance, maneuverability, stability and stealth tighten with each new generation. Fully understanding the hydrodynamics of the vessels is key if performance requirements need to be met. In this paper, the numerical simulation with three different turbulent models, Reynolds averaged Navier-Stokes (RANS) Realizable k-ε model, RANS SST (Menter’s Shear Stress Transport) k-ω model and the large eddy simulation (LES) are used to simulate the self-propulsion of DARPA SUBOFF submarine under V = 2.755m/s, and the simulation results are compared and analyzed. The comparisons show that the RANS method can be used to simulate the drag and pressure of submarine self-propulsion accurately. The surface pressure of LES is more accurate for fine flow field, the simulation of self-propelled parameters is less as accurate might because the mesh is not refine enough.

As a type of the ship stability failure modes, parametric rolling has attracted more attention from many researchers in recent years because of a series of accidents due to ship instability, especially the instability of container ship. Parametric rolling is a complex nonlinear stochastic dynamic problem, which is often accompanied by large amplitude vertical motions of ships. At present, there are many difficulties in the research of ship parameter rolling, mainly including the nonlinearity of parameter rolling motion, the random variation of wetted area of the hull surface up to the incident wave waterline and the coupling effect of rolling, pitching and heaving. Nowadays, the potential flow theory is a common method to predict parametric rolling, but this method may generate results with low accuracy in some conditions. This paper describes a numerical simulation method based on in-house CFD code HUST-Ship to analyze parametric rolling motion of KCS (KRISO Container Ship) container ship model. The paper studies the occurring conditions of parametric rolling motion of KCS model and reveals the mechanism of parametric rolling.

This paper presents CFD simulation results of the stern flap effect with different lengths for hydrodynamic performance of catamaran moving in calm water, including resistance and sailing attitude. Inhouse viscous CFD (computational fluid dynamics) code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) is used for the study. The catamaran with/without stern flap with different lengths were studied. The trim and sinkage of the catamaran were solved coupled with flow solver. Experimental studies in calm water were conducted to validate the numerical method. The comparison of hydrodynamic performance of catamaran with stern flaps of different lengths was made. The results show that the stern flap can reduce the sailing attitude and has influence for the resistance of catamaran at high-speed.

The key objective of this paper is to perform a fully nonlinear unsteady RANS simulation to predict the self-propulsion performance of KCS at two different scales. This simulations are performed at design speeds in calm water, using inhouse computational fluid dynamics (CFD) to solve RANS equation coupled with two degrees of freedom (2DOF) solid body motion equations including heave and pitch. The SST k-ω turbulence equation is discretized by finite difference method. The velocity pressure coupling is solved by PISO algorithm. Computations have used structured grid with overset technology. The single-phase level-set method is used to capture the free surface. The simulations of self-propulsion are based on the body-force method. The PID control method is applied to match the speed of KCS by changing the propeller rotation speed automatically. In this paper, the self-propulsion factors of KCS at two scales are predicted and the results from inhouse CFD code are compared with the EFD date, and then the reasons for the scale effect have been discussed.

This paper presents CFD to study the hydrodynamic performance for the high-speed, multi-hull Catamaran advancing in calm water. It uses inhouse computational fluid dynamics (CFD) code to solve RANS equation coupled with six degrees of freedom solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Computations have been made using structured grid with overset technology. Turbulence models used the anisotropic two equations Shear Stress Transport (SST) k-ω model. Single phase level set was used for free surface simulation. A good agreement on the resistance prediction between CFD and experimental fluid dynamics (EFD) has been observed (on the resistance prediction of about 4.0%). Differences between CFD and EFD have been seen for the 3 degrees of freedom (3DOF) motion, whereas larger discrepancy is observed for the sinkage and trim estimation (about 8.0%).

The dolphins’ cruising, generally, with an extremely high thrust efficiency and low drag, which attracted many researchers’ wide attention. It is hoped that we can improve the hydrodynamic performance of underwater vehicle by studying the thrust characteristics of dolphin’s kick and the relationship between the formation of vortex and the thrust generation. However, previous work is mostly focused on investigation of hydrodynamic performance of dolphin fluke motion with a rigid tail which means that the locomotion of caudal fin is defined only by the oscillating motion, without the chordwise deformation. In this paper, the dolphin’s fluke motion is realized by a flexible caudal fin which is defined by a combination of oscillating motion and chordwise deformation. The simulation of the dolphin fluke motion is achieved by STRA-CCM, and dynamic moving mesh is implemented for different stroke functions. This paper primarily analyzed the thrust characteristics and the formation of vortex of dolphin fluke motion, then compared with the available data from previous work with rigid tail. It can be found that the structure of the vortex generated by the dolphin fluke motion with flexible caudal fin is different from a rigid one. Finally, by analyzing the instantaneous flow condition behind the dolphin caudal fin, it can get the reason why the thrust generated by the flexible caudal fin is larger than rigid one.