Design and load reduction performance analysis of mitigator of AUV during high speed water entry

The Autonomous Underwater Vehicle (AUV) will suffer severe impact load during the water entry, and its shell structure will undergo elastoplastic deformation, even breakage or damage, which seriously threatens the safety and reliability of the AUV. Therefore, it is necessary to carry out research on the buffering technology of the impact load of the vehicle into the water to ensure that the AUV can enter the water safely and reliably. In this paper, a mitigator is designed to reduce the impact load of the AUV entering the water. Numerical simulations based on the explicit finite element method with an Arbitrary-Lagrangian Eulerian (ALE) solver are carried out to study the mitigation characteristic of the designed mitigator. The accuracy of the model was verified by the experimental results of the water-entry of the small sphere, and the mesh independence was verified to determine the mesh size. Then, the effects of initial conditions such as buffer length, buffer material density, entry velocity and entry angle on the cushioning effect of the buffer head cap were studied. When the vertical water entry velocity is 50 m/s, the impact load reduction ratio is 42.2%; while the water entry angle is 60 degrees and the water entry velocity is 50 m/s, the axial load reduction ratio is 28.8%, and the normal load reduction ratio is 27.8%. These conclusions will be useful for the designing of the crashworthy structural and the analysis of underwater weapon impact.