Characterization of Surface Motion of Submerged Unmanned Ship in Freak Waves Environment

When a ship encounters abnormal waves, the instantaneous impact will cause a drastic change in the wave load, potentially leading to capsizing in serious cases. To investigate the special ship type that can effectively withstand the impact of freak waves, this paper explores a certain type of submerged unmanned ship with excellent adaptability to high-intensity wave loads under extreme sea conditions, and analyzes its motion characteristics under various wave environments. First, based on the Reynolds-averaged Navier-Stokes equations (RANS), the effects of the fifth-order Stokes waves and freak waves with different wave amplitudes on the water surface motion of the unmanned ship are taken into account. Then, the motion of ship pitch and heave in two degrees of freedom is analyzed by using the dynamic fluid body interaction (DFBI) model. Finally, the simulation results are visualized to analyze the surface pressure of the hull, the total resistance, the motion response, and the load characteristics of the ship. The results show that as wave amplitude increases, the wave load of the submerged unmanned ship also increases, and the motion response becomes more intense. Compared with the fifth-order Stokes waves, the wave load of the unmanned ship in deformed wave is smaller, which is advantageous for the safety of the hull structure, because the head of the submerged unmanned ship combines the advantages of a conical bow and a bulbous bow, allowing it to disperse and divide the wave flowing through the bow, and effectively inhibit the impact of the wave. This effectively suppresses the impact of the waves and ensures the safety of the unmanned ship in extreme sea conditions. The results of this study can provide technical support for the safe navigation of submerged bow-type unmanned ship in extreme sea conditions, such as freak waves.