The vertically launched underwater vehicle always suffers various hydrodynamic disturbances in its water-emerging process due to the uncertainty of the launch platform motion. Based on the nested sparse grid based stochastic collocation method (NSSCM) and nonintrusive polynomial chaos method, the effect of uncertainty of platform velocity and yaw angle on robustness of vehicle's trajectory and attitude is numerically studied. Results indicate that the uncertainty stemming from platform motion propagates along vehicle's water-emerging process. As the negative horizontal velocity of vehicle gradually changes to positive direction, the uncertainty bar of horizontal velocity presents contracting-expanding mode with an “hourglass” shape while the uncertainty bar of horizontal displacement experiences a “spindle-shaped” one (expanding-contracting-expanding), which is a half cycle later compared with the velocity. The uncertain motion of platform enlarges the uncertainty bar of bottom force via its impact on the gas-leakage process of trail bubble, resulting in the increasing of uncertainty of vertical velocity. Pitching angle (attitude of vehicle) and pitching angular velocity of vehicle persist getting worse driven by the pressure difference between vehicle's front and back sides especially on head part. And their continuous increasing uncertainty bars are formed mainly due to the condition that pressure uncertainty of front side is larger than that on back side, which also leads to the increasing of uncertainty of horizontal force.

The formation and development of attached cavities on the surfaces of underwater moving vehicles involve complex multiphase flows, which are critical for determining the load characteristics and motion stability of the vehicles. This study utilized experimental methods to investigate the formation process and motion characteristics of these attached cavities. Pressure sensors mounted inside the acceleration tube captured the relationship between cavity evolution and transient pressures. High-speed cameras were employed to observe the shedding morphology of the ventilated shoulder cavity, analyzing the mechanism behind its gas cutoff. The findings reveal that the negative pressure impact during the vehicle's tail exit from the tube is crucial for the gas cutoff of the shoulder ventilated cavity. Additionally, increasing the internal cavity pressure ratio significantly influences the size development of the shoulder cavity. At a constant pressure ratio, different hole ratios have a negligible effect on the axial development of the shoulder cavity. When the number of holes increases and the hole ratio decreases, it promotes the circumferential fusion of the enlarged shoulder cavity and enhances the coverage of gas on the vehicle's surface.

The formation and development of an attached cavity at the tail of an underwater moving vehicle involves a complex multiphase flow, which determines the load characteristics and motion stability of the vehicle. In this study, an experimental method was used to explore the formation process and motion characteristics of the cavity at the tail of the vehicle, and a pressure sensor installed at the tail of the model was used to establish the relationship between the evolution of the tail attachment cavity and transient pressure. The study found that the process of pulling and breaking the attached cavity was accompanied by the generation of bidirectional jets, and reducing the cavitation number could weaken the occurrence of jet impact. When the ventilation flow reaches the critical value ${\overline{Q}}_{in}$ = 1.28, the cavity pulsates. In addition, increasing the ventilation flow does not increase the size of the tail cavity, and the length of the cavity at the closure increases with the decrease of the cavitation number.

The development of the tail cavity is a key factor influencing motion stability and structural reliability during water exit, making the study of dynamic pressure evolution crucial. In a high-pressure gas launch experiment, the dynamic pressure evolution of the tail cavity was investigated under varying ventilation pressures and durations, revealing three typical pulsating flow patterns: first order, second order, and third order. Additionally, the impact of pulsation frequency, relative cavitation number, and relative Froude number on the tail cavity's evolution was examined, with underlying mechanisms explained. The results show that the internal and external pressure differences, coiling suction effect, and differences in medium inertial suppression forces are the primary contributors to wake surges. Notably, changes in pulsation order result in abrupt shifts in the principal frequency of pressure pulsation. The pulsation frequency is positively correlated with ventilation pressure and negatively correlated with ventilation duration. Based on the relative Froude number, the tail cavity's dynamic evolution was classified into three states under constant ventilation pressure: the average state, the gas leakage and shedding state, and the post-shedding growth state. Tail cavity shedding was further classified as stable or unstable, depending on the aeration parameters. The relative cavitation number of the tail cavity in the third-order pulsation ranged from 0.2 to 1.4. As the pulsation order decreases, the relative cavitation number at the initial and water-exit moments increases.