Study on the oblique water entry impact performance of AUV under different launch conditions based on coupled FEM-ALE method

In this study, the hydrodynamic response of an autonomous underwater vehicle (AUV) subjected to oblique water entry impact is investigated by employing an explicit FEM technique with arbitrary Lagrangian–Eulerian formulation. The predictive ability of the employed numerical model is validated by correlating the cavity evolution of AUV and peak impact accelerations with the experimental outcomes of the previous research work. The influence of advection algorithms on the water entry phenomenon is studied. It is found that the first order donor cell advection scheme is more suitable for low speed impact problems as it is computationally more efficient. However, for high speed water entry simulations, the van Leer advection scheme gives more accurate results. Moreover, using different water entry angles, the effect of the angle of attack (AOA) and length of AUV and its head shape on the impact performances are investigated and discussed. The results show that the radial impact load is more likely to be influenced by AOA and the effect of AOA on the radial impact load is more significant for a small water entry angle, i.e., 30°, as compared to a large entry angle, i.e., 60°. It is also observed that AUV of a smaller length shows the ricochet behavior at a water entry angle of 30°. It is seen that the head shape has a substantial effect on the axial and radial impact loads and velocity attenuation of a vehicle under water. The conclusions drawn in this research work will be beneficial for the selection of appropriate initial launch conditions and for the designing of an AUV structure.