Numerical investigation of the hydrodynamic characteristics and interactions of an unmanned surface vehicle chasing a mother ship during recovery

Unmanned surface vehicles (USVs) require efficient and reliable recovery at sea. However, the recovery process, involving USVs chasing a mother ship, is complex and risky due to wave-making and wake effects that impact USV stability and resistance. It is necessary to study the interaction between the USV and the mother ship during the docking process in order to understand the changes in the motion performance of the unmanned ship during docking and provide a basis for the subsequent optimization of the control method and recovery path of docking recovery. This study numerically simulates the hydrodynamic behaviors of a 175-USV developed by Huazhong University of Science and Technology chasing alongside a KRISO Container Ship (KCS) standard model during recovery. 175-USV lake tests and corresponding simulations were compared and analyzed, which show good accuracy. Simulations reveal time-varying hydrodynamic characteristics as the USV operates into calm water, in coming waves of varying amplitudes and directions. Findings show roll angles and moments fluctuate within the location range of 35-45 % of the mother ship length to the stern, with swaying force peaking near the location of 10 % of mother ship length to the stern due to suction effects. Waves increase motion responses and loads, especially under oblique wave conditions, yet smoother regions persist on the opposite side of incoming waves. This study reveals the interaction between the hydrodynamic properties and the ship during docking, which supports the safe and reliable recovery of unmanned vessels.