For the purpose of studying the feasibility of deep-sea vehicles with damping plate deceleration mechanism achieving a safe water-exit velocity, the hydrodynamic coefficients of body and mathematical model of the damping plate deceleration mechanism are estimated by using computational fluid dynamics (CFD). CFD model is performed to simulate extensive captive model tests including axial drag tests and planar motion mechanism (PMM) tests and explore the effect of oscillation frequency and amplitude on the hydrodynamic coefficients. The dynamic expansion process of the damping plate is discretized to analyze its axial drag force in steady motion at different expansion angles and velocities. The mathematical model of damping plates is established by fitting its axial drag force with least-squares method. The deceleration motion of the vehicle with dynamic deployment of damping plates is simulated based on Simulink model. The result indicates the unpowered vehicle with damping plates can realize a safe water-exit velocity uζ≤1m/s. Relevant research provides a reference for the hydrodynamic modelling of body and damping plate deceleration mechanism.
The ascent process of the deep-sea unpowered vehicle is divided into two stages: rapid ascent and deceleration motion before exiting the water. The vehicle adopts vertical attitude to achieve a greater vertical velocity during rapid ascent phase. It needs to decelerate before exiting the water to ensure the safe water-exit velocity of the unpowered vehicle, which reduces the impact load of the vehicle of re-entry water. Because of the vehicle without propeller, it is difficult to decelerate due to the added mass force from fluid during deceleration process (Quan, 2020). Therefore, it is necessary to design an effective deceleration device.
The deceleration mode of unpowered underwater vehicles has various forms, such as deceleration parachute, deceleration wing, ballast tank and so on. Lian, Wang and Sun (2019) established the mathematical model of parachute deceleration and cabin separation landing motion for the underwater safe landing of latent weapons with parachute, and studied the influence of different opening angles of parachute on the landing motion process and the law of submarine weapon separation deceleration sitting bottom motion by numerical calculation method, but the influence of the dynamic parachute opening process on the landing movement is not considered. Sun and Huang (2020) analyzed three deceleration schemes for installing ballast tanks, deceleration parachute and deceleration wing in the large escape capsule for submarine, all of which can control the safe water-exiting speed, and the deceleration wing scheme is the best. Ren and Bian (2018) found that the existence of the damping plate will increase the axial additional mass of the underwater vehicle and reduce the tail flow velocity through the simulation analysis of the flow field, and the deceleration effect is obvious. Bian, Zhao, Li and Zhu (2017) constructed a mathematical model of the trajectory of a vehicle with reverse damping plate, and used the orthogonal test method to optimize and analyze the three parameters of the number, size and expansion angle of the damping plate of the underwater vehicle.