Mechanical characterization of flat faced deformable AUV during water entry impact considering the hydroelastic effects

In this paper, the dynamic behavior of flat faced deformable autonomous underwater vehicle (AUV) subjected to hydroelastic water entry impact is numerically investigated by using Arbitrary Lagrangian Eulerian (ALE) method. The experiments on the flat faced AUV head section of 200 mm diameter are carried out in a water tank to validate the numerical model by comparing the impact accelerations and underwater cavity evolution by using accelerometers and high speed cameras. Then, the effect of hydroelasticity is numerically investigated by comparing the impact characteristics of rigid and deformable AUV with different rigidities. It is revealed that the hydroelastic effect increases with the decrease in the rigidity of the structure. Mechanical behavior of deformable AUV of various rigidities under the initial conditions of same velocity, same kinetic energy and same mass is examined. The influence of various initial conditions on the hydrodynamic load, impact pressure and effective strain for deformable AUV are discussed. The influence of the water entry angle and impact velocity on the semi-rigid and deformable AUVs are also studied. It is found that the effective strain increases exponentially with the increase in impact velocity and entry angle for deformable AUV, however, semi-rigid AUV exhibit linear strain behavior. Numerical conclusions drawn from this study are vital in selecting the rigidity of AUV and highlighted the influence of hydroelasticity for flat faced AUVs. Additionally, the results obtained in this study can be beneficial for the structural design of high speed air launched AUVs.