Water entry slamming is a complicated issue in marine engineering, characterized by significant impact loads and complex flow. This paper establishes a 3D numerical model of flat plate water entry slamming based on smoothed particle hydrodynamics (SPH), and the dynamics and flow field evolution are analyzed during water entry. The results indicate that SPH effectively captures the key dynamic characteristics of flat plate water entry. The experimental data validate the model, and the SPH particles reproduce the phenomena of jet formation, cavity development, and fluid splashing. The observed pressure is maximum at the center of the flat plate, and the maximum pressure and vertical force of the flat plate exhibit a quadratic relationship with the water entry velocity. The flow field evolution from initial jet formation at the time of slamming to droplet splashing shows obvious stages. As the water entry depth of the flat plate increases, the growth rates of the cavity width and splash height gradually slow under fluid viscosity and drag. The water entry velocity has the greatest influence on droplet splashing, whereas its influence on the jet separation point and the position of the free liquid surface is less significant.

The flow memory effect is a kind of viscous force caused by acceleration between continuous phases and underwater vehicles and the development of the boundary layer near the interfacial surface. This paper establishes a 6‐degrees‐of‐freedom unsteady equation of motion describing the flow memory effect on viscous hydrodynamic loads. Motion simulations based on the unsteady and steady equations of motion for a work‐class open‐frame remotely operated vehicle are studied. Comparative studies show that the flow memory effect decreases the roll amplitude by over 50% at the natural frequency and has a greater impact on the motions in directions without control forces. The flow memory increases the lateral distance of rotation motions by over 10%. Under the flow memory effect, velocity fluctuations that persist over 2–5 times the length of the remotely operated vehicle are induced after the thrust control stops. The application of the unsteady equation of motion as part of a controller is verified through simulation experiments. A sudden motion in the process of rotation is designed to study the improvement of the control ability of the unsteady model. The experimental results suggest a performance improvement of ~30% over the steady‐model‐based controller when the roll angle error reaches the extreme value. The lower sensitivity of the unsteady‐model‐based controller is proved by motion control under multiple gains.

Water entry is a complex process in marine engineering, marked by highly dynamic and intricate flow behavior. This study investigates the dynamic characteristics of cavity evolution during the water entry of a porous plate through experimental and numerical methods. A numerical model based on the smoothed particle hydrodynamics (SPH) method was developed and validated against experimental data under various velocities. The results indicate that the model accurately captures key stages of cavity evolution, showing good agreement with experiments across different velocity values. Detailed analysis of cavity and jet evolution reveals distinct mechanisms of jets driven by pressure distribution, along with corresponding energy dissipation patterns. Parametric studies indicate that cavity width, pinch-off time, and jet height all exhibit a linear positive correlation with water-entry velocity, with jet height being more sensitive to variations in velocity. The cavity and jet of the porous plate are smaller than those of the flat plate under the same conditions. Furthermore, post-pinch-off flow field evolution exhibits four typical dynamic zones, where interactions between upward and downward flows induce significant velocity fluctuations of the porous plate. These findings provide theoretical insights into the hydrodynamic behavior of porous structures during water entry and offer valuable guidance for modeling and optimizing impact problems in marine engineering applications.