A hybrid collision model for the fluid–structure interaction during autonomous underwater vehicle recovery

Underwater recovery technology is critical for the deployment and recovery of autonomous underwater vehicles (AUVs). In fact, collisions between the vehicle and the recovery device can lead to recovery failures due to the strong fluid–structure interaction (FSI) that exists between the AUV and the flow field. Therefore, the real-time hydrodynamic effects during this process cannot be ignored. This study proposes a hybrid collision model (HCM) to simulate active and passive AUV recovery with a petal mechanism grasper (PMG), which integrates the AUV dynamic model, the PMG kinematic model, and a collision dynamics model based on reflection theory and the momentum theorem. The AUV dynamic model and PMG kinematic model establish the six-degree-of-freedom dynamics of the AUV and the kinematics of the PMG, respectively. The collision dynamics model accurately describes the collision process between the AUV and the PMG. The overset grid method is employed to address computational challenges associated with multi-body contact between the PMG and the AUV, enabling precise simulation of the motion trajectory and attitude variation of the AUV, as well as the hydrodynamic forces of the PMG and AUV, during recovery. The correctness and applicability of the proposed method are verified through numerical simulation and a pool experiment. Results demonstrate that the HCM can capture the hydrodynamic changes of the AUV during multiple collision scenarios in real time to accurately simulate the motion performance and attitude variations. In brief, the proposed model can effectively reflect the FSI characteristics of the underwater recovery process, and the current study provides new theoretical and methodological support for the safe and efficient recovery of AUVs.