Ricochet Characteristics of AUVs during Small-Angle Water Entry Process

When the autonomous underwater vehicle (AUV) enters the water at a small angle, the head of the AUV will be subjected to a torque that causes it to rise, which may cause the AUV to ricochet. The occurrence of ricochet will have an important impact on the trajectory stability of the AUV. In this paper, the finite element method-smoothed particle hydrodynamics (FEM-SPH) coupling algorithm, which absorbs the high efficiency of FEM and the advantages of SPH in dealing with large deformation and meshes distortion, is used to study the small-angle water entry problem of the AUV numerically. In the coupled FEM-SPH algorithm, discrete particles were used to model the zone of water, while the part of the AUV was modeled with finite elements. A contact algorithm couples the finite elements and the particles. Particular attention was paid to the influence of different head hemisphere angles and different initial conditions on the ricochet trajectory of the AUV. The critical conditions and influencing factors of the AUV ricochet phenomenon were given.