FSI simulation of water entry impact of three-dimensional rigid AUV under different initial parameters

High speed water entry of Autonomous Underwater Vehicle (AUV) is highly transient and complex process and are subjected to huge impact loads which may cause structural damage to the AUV and inner sensitive equipment. Therefore, accurate modeling of the phenomenon, trajectory calculation and accurate prediction of hydrodynamic impact loads of vehicle at various launch conditions are of paramount importance. In this article, we study the impact characteristics of air launched AUV under different initial parameters during high speed water entry. For this purpose, numerical model based on coupled explicit finite element method (FEM) and arbitrary Lagrangian Eulerian (ALE) scheme is established. ALE method is suitable for large deformation FSI simulations because it encompasses both Lagrange and Euler formulation. The fluid motion is analyzed in the Eulerian formulation, whereas the Lagrangian method is used to track the movement of vehicle and the free surface. The reliability of the applied numerical model is verified by the experimental results of the earlier study. Then, the influence of angle of attack (AOA), initial pitching moment and variation in AUV mass on water entry of rigid AUV are investigated. It is observed that impact loads rises with the increase in the attack angle. Radial load is more sensitive to change of AOA. Results also show that, for negative AOA, radial force of AUV alters its direction after initial impact. It is also witnessed that the vehicle mass has significant effect on the impact load. Some linear and nonlinear relationships between the impact characteristics and initial launch parameters are deduced. The research conclusions provide guidance for the design of AUV by selecting appropriate water entry conditions.