Payload Bay Berthing of Underwater Vehicles with a Larger XLUUV

Extra-large unmanned underwater vehicles (XLUUVs) present an opportunity to launch and recover (LAR) smaller autonomous underwater vehicles (AUVs) covertly in contested regions, increasing their operational range, time on station, data transmission and operational safety. Berthing onboard an XLUUV is fundamentally different to berthing with static and towed docks, due to an XLUUV's physical size, movement speed and propulsion system. This affects the pressure, drag, turbulence and flow fields that a smaller AUV would experience whilst conducting such a berth. To conduct these underwater LAR manoeuvres using an XLUUV, the nature and magnitude of the hydrodynamic effects exerted on the smaller AUV must be understood. This investigation assesses if a propeller-rudder vehicle (under-actuated) or a thruster driven (over-actuated) vehicle can be used for berthing as the ways in which these vessels maintain control authority and overcome forces are different. The hydrodynamic effects and forces during berthing are modelled using ANSYS Fluent and are recorded as the AUV body is incremented along a trajectory from astern of the XLUUV, through the boundary layer and into the payload bay of the XLUUV. Subsequently, it was determined that the over-actuated vessel is likely the only practical option. The lack of pitch and control authority for the under-actuated AUV will render it uncontrollable once located in the payload bay. Experimental testing should be conducted to further validate the phenomenon and findings presented. It is hoped the findings of this investigation will serve as a starting point for the recovery of AUV platforms using an XLUUV's payload bay.