The high-speed projectile moving near the sea level will significantly suffer from the effects of waves. The water entry and exit of a high-speed projectile crossing a wave are investigated by detached-eddy simulation. Three simulations with different altitudes through the wave are conducted to analyze the altitude's influence on the cavity dynamics. To validate the numerical model, a water-entry experiment is carried out in a wave tank for comparison. The projectile crossing the wave forms a cavity channel from water entry to exit. Because the water below the cavity is more difficult to displace than the atmosphere with the water surface under the cavitation effects, the downward expansion of vapor is blocked, and the wave surface is lifted. Consequently, the cavity above the projectile expands more strongly until breaking through the water surface, while the cavity below the projectile keeps closed, and the projectile is wetted. Thus, a nose-up pitching moment is generated at water entry, while the drag force is gradually enhanced during the water exit, and a lift force acts toward the atmosphere. As the altitude increases, the upper cavity becomes more open, but the lower cavity shrinks, leading to the augmentation of the lift force.

Structural health monitoring (SHM) of composite materials is of great significance in various practical applications. However, it is a challenge to accurately monitor the damage of composites without affecting their mechanical properties. In this paper, an embedded sensing layer based on carbon nanotube-coated glass fiber is designed, combined with electrical resistance tomography (ERT) for in situ damage monitoring. Multi-wall carbon nanotube-coated glass fiber (MWCNT-GF) is prepared and embedded into laminates as an in situ sensing layer. Low-velocity impact experiments demonstrate that the embedded sensing layer has high compatibility with the composite laminates and has no adverse effect on its impact response; although, the energy absorption behavior of glass fiber-reinforced polymer (GFRP) laminates containing MWCNT-GF occurs about 10% earlier than that of GFRP laminates overall. ERT technology is used to analyze the laminates after a low-velocity impact test. The results show that the in situ monitoring method with the embedded MWCNT-GF sensing layer can achieve high precision in imaging localization of impact damage, and the error of the detected damage area is only 4.5%.

An experimental study was conducted with the aim of alleviating the vertical tail buffeting of a 55° delta wing using pulsed nanosecond dielectric barrier discharge plasma actuators. The flow physics in the event of wing stall, flow reattachment, vortex breakdown, shear layer under plasma actuation were obtained and analyzed, and results indicate that plasma actuation promotes flow attachment and manipulates the shear layer. The acceleration results indicate that the structural response of the vertical tail increases with an increasing angle of attack, and the first bending mode response increases most significantly at the post-stall angle. Manipulation of flow field by plasma actuation produces a considerable reduction in buffeting response and mainly controls the first bending mode. The characteristics of velocity fluctuations show two important factors affecting buffeting: the redistribution of loads and the spectrum change of fluctuations, both of which are related to the movement of the impingement point of the shear layer onto the vertical tail controlled by plasma actuation. Theoretical analysis indicates that the impingement point moving downward in the vertical direction of the vertical tail under plasma actuation is the main reason for reduction of the first bending mode response.

The water-entry cavity sealing of elliptical cylinders is systematically investigated with experimental methods, which features the inconsistent lengths of major and minor axes. By comparing with the cylinder entering water, the effects of aspect ratio and Froude number on the cavity sealing are analyzed to reveal the mechanism of sealing mode transformation among deep, transition, and surface seals. In the deep seal mode, the water-entry cavity of cylinders pinches off at a singularity, but the minor-axis cavity of elliptical cylinders shows an oval hole when the cavity in the major axis pinches off. During the water entry of elliptical cylinders, the water hardly splashes in the major axis but mostly splashes in the minor axis. Thus, the minor-axis cavity is larger than the major-axis cavity in the surface seal. Especially, when the splash crown seals to the tail plane, the transition seal mode occurs with surface and deep seals successively appearing. The shedding cavity in the deep seal of cylinders is penetrated by a central water column, while the shedding cavity of elliptical cylinders merges with the downward jet and splits into two separate halves. As the aspect ratio increases, the minor-axis splash crown obtains more kinetic energy and gradually expands outwards. Consequently, the deep seal happens later with a larger pinch-off depth, but the surface seal occurs faster with a smaller cavity volume. Therefore, the sealing mode transformation sequentially undergoes surface, transition, and deep seals, which is contrary to the mode transformation with the increment of Froude number.

A trajectory control method is proposed for the rapid leveling of the projectile after water entry through an asymmetric head-type design. The hydrodynamic and trajectory characteristics of truncated head-type projectiles were investigated using high-speed experiments and numerical simulations based on Reynolds-averaged Navier–Stokes (RANS) equations coupled with the volume of fluid (VOF) method. The effects of truncation angle and water-entry velocity were systematically examined. The results show that all truncated head-type projectiles exhibited rightward-deflected trajectories, with larger truncation angles producing greater lateral deviation and trajectory curvature. This behavior is attributed to asymmetric water impact, where non-uniform flow around the projectile generates distinct cavities at the head and tail, respectively, resulting in lateral forces and yaw moments. The initial impact induced sharp peaks in drag, lateral force, and yaw moment coefficients. As the projectile interacted with the cavity surface, projectiles with larger truncation angles experienced earlier cavity collisions and faster stabilization. In contrast, variations in water-entry velocity had little influence on centroid trajectories and hydrodynamic coefficients at comparable penetration depths. An empirical trajectory model was developed by decoupling the equations of motion to relate trajectory curvature to truncation angle. The model demonstrated excellent agreement with numerical results, providing a reliable predictive tool for the design and control of water-entry projectiles.

The effects of rotational motion around the central axis of a supercavitating underwater cylindrical vehicle are numerically investigated with the cavitation process at a cavitation number of 0.0198. The relationships among tangential velocity, streamwise vorticity, flow field pressure distribution of the flow field, mass transfer rates of water and water vapor, and cavity shapes are analyzed under varying rotational speeds. Compared to non-rotational motion, the distinct cavitation mechanisms in rotational motion are identified. The results indicated that during the initial cavitation stage, the tangential velocity near the vehicle's surface rises as the rotational speed increases, gradually decreasing the pressure and transforming water into water vapor. Simultaneously, the concave structure at the end of the front cavity near the vehicle's surface progressively disappears. This accelerates the cavitation process, causing the earlier merger of the front and rear cavities. Following this process, a concave structure appears at the center of the cavity tail for the non-rotating vehicle due to the pressure increase. However, this concave structure gradually transforms to a convex structure with increasing rotational speed. This phenomenon is attributed to the tangential velocity generated by the vehicle's rotation, which causes the pressure in the rear cavity to rise very slowly, and the low-pressure region contracts toward the axis line. The mass transfer in the rear cavity of the rotating vehicle is significantly improved with pressure changes, transforming from vapor into water. Therefore, the pressure changes and mass transfer rate induced by rotation lead to converting the rear cavity end from a concave to a convex structure.