Research on load and motion response characteristics of a water-entry vehicle with different rudder angles

During high-speed oblique water entry, the continuous impact load experienced by the vehicle can lead to structural damage and influence trajectory stability. This article investigates the load and motion response characteristics of the vehicle with different rudder angles during the entire high-speed water entry process. In the numerical methods, a quaternion-based six degrees of freedom motion system is employed to describe the rigid body motion, while a multiphase Eulerian finite element method serves as the fluid solver. An experiment is conducted to verify the accuracy of the numerical method. Furthermore, the mechanisms underlying the formation of tail slamming normal loads during high-speed oblique water entry of the vehicle at different rudder angles are explored. The loads including axial force coefficient, normal force coefficient, and pitch torque coefficient are extensively discussed. Results indicate that the tail slamming phenomenon and the vehicle's trajectory are significantly influenced by the rudder angle. The design of positive and negative rudder angles causes both the upward and downward tail slamming. The “excellent rudder angle range α̃” for the vehicle during high-speed water entry is defined. Selecting a rudder angle design within this range can effectively reduce the normal load during the tail slamming events, it can result in decreased pitch torque amplitude and form a straighter, more stable trajectory. This work provides new insights into load control during vehicle steering.