To understand the multiple tail-slapping the trans-media vehicle going through during the high-speed water entry, which may cause damage to the main structure and its accessories. The study was conducted to investigate the load characteristics of the main body of the trans-media vehicle and its accessories in the stages of the generation, development, and collapse of cavities under the condition of inclined water-entering with an attack angle, based on the VOF multiphase flow method. The influence of the water entry inclination angle on the tail-slapping load, cavity collapse load and the trajectory stability are revealed. The results show that the cavity collapse stage is the most dangerous working condition during the water entry process. As the water entry inclination angle increases, the axial and normal forces on the structure increase in the cavitation collapse stage, while the normal overload coefficient approaches a constant. When the inclination angle into the water increased from 60° to 90°, the pitch moment coefficient of the structure increased by 47.1%. A larger inclination angle can reduce the axial and normal loads of the horizontal rudders during the cavity collapse stage, and also improve the trajectory stability of the vehicle. However, it will increase the axial loads of the vertical rudders at the same time. When the cavity wall impacts the tail of the trans-media vehicle during the cavity collapse stage, the three-directional rotation of the body is suppressed, causing it to be in a brief state of rest.
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Open Access
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This study aims to investigate the dynamic behavior and flow field characteristics of trans-medium submersibles during underwater straight-line navigation and turning maneuvers.
To this end, computational fluid dynamics simulations were employed, using the VOF multiphase flow model and the SST k–ω turbulence model to establish a numerical model of the underwater navigation of the trans-medium submersibles. The accuracy of the numerical method was validated by comparing the experimental total drag data for the DARPA Suboff submarine model at various speeds with the numerical calculation results. On this basis, numerical simulations and analyses of underwater straight-line navigation and turning maneuvers of the trans-medium submersible were conducted, focusing on the effects of ducted propeller rotation speed and tail fin deflection angle on the underwater straight-line navigation and turning performance of the submersible.
The research results indicate that during straight-line underwater navigation, the forward speed of the trans-medium submersible exhibits an approximately linear relationship with the propeller's rotational speed. For instance, as the propeller speed increases from 600 r/min to 4800 r/min, the forward speed rises from 1.1 m/s to 8.1 m/s. At the same time, the pitch moment becomes less negative with increasing propeller speed (from −0.35 N·m to −0.17 N·m), indicating that the submersible remains stable in pitch during high-speed navigation. The propeller speed has little effect on the surface pressure distribution and the structure of the surrounding flow field. During underwater turning, the turning radius is mainly determined by the tail fin deflection angle and is largely unaffected by the propeller speed. The turning radius decreases with increasing tail fin deflection angle (from 3.35 times the submersible's body length to 0.75 times), though the rate of decrease diminishes. In contrast, the turning speed is affected by both the propeller speed and the tail fin deflection angle. The thrust generated by both propellers increases with higher propeller speeds and larger tail fin deflection angles. During turning, the thrust of the outer propeller consistently exceeds that of the inner propeller, and the thrust difference increases with greater tail fin deflection. Furthermore, tail fin deflection during turning leads to a significantly asymmetric surface pressure distribution on the submersible. This asymmetry becomes more pronounced with increasing tail fin deflection and is closely associated with the asymmetric flow characteristics of the surrounding flow field.
This study provides a reference for the design and performance analysis of trans-medium submersible configurations.
Open Access
Issue
In order to study the characteristics of vehicle water entry at high speed in the fragmented ice environment, such as the evolution of cavitation flow field, vehicle dynamic response and ice breaking load characteristics, a coupled computational model of fluid-structure interaction for high-speed water entry of the vehicle in fragmented ice environment was established based on the Arbitrary Lagrangian-Eulerian method (ALE). The high-speed water entry process of a round-nosed vehicle was investigated through experiments and numerical calculations, validating the effectiveness of the high-speed water entry computational method. By comparing the results of the three-point bending test of the ice material with the numerical results, the reliability of the ice material model used in the calculations was verified. Using the constructed coupled computational model of fluid-structure interaction, the high-speed water entry process of a vehicle in a fragmented ice environment was studied and analyzed. The research focused on the effects of fragmented ice and the gaps between ice fragments on the flow field, dynamic parameters, and loads during the water entry process of the vehicle.The results show that the presence of fragmented ice has an inhibitory effect on the water surface lift and the evolution of splashing after the water entry of the vehicle. In the fragmented ice environment, the impact load on the vehicle during water entry significantly increases, and the process involves greater kinetic energy loss compared to a non-ice environment. However, the duration of the slamming load is consistent with water entry in a non-ice environment. The continuity of the splash crown formed during water entry increases with an increase in the gaps between ice fragments. Within a certain range of ice gaps, the instantaneous slamming load on the vehicle shows a negative correlation with the size of the gap. When the gap is sufficiently large, the variation in the slamming load becomes relatively small.
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