Study On Hydrodynamic Interaction And Motion Response Of Autonomous Underwater Helicopter Near Water Surface

With the increasing demand for natural resources in human society,the ocean has gradually become the focus of attention because of its rich resources.The high performance submersible,as a flexible underwater vehicle,can perform underwater tasks such as resource exploration,scientific investigation and lifesaving,which has attracted wide attention in recent years.When the submersible is close to the scientific mother ship with a larger scale than itself,the hydrodynamic performance will undoubtedly be greatly affected.Therefore,it is very important to study the hydrodynamic interaction on the seakeeping,maneuverability and safety of the submarine when it is launched and recovered by the scientific mother ship.In this paper,the hydrodynamic analysis software ANSYS-AQWA which is based on the three-dimensional potential flow theory is used to calculate the near-surface motion response of a circular autonomous underwater vehicle—underwater helicopter.It is used as the research object,and the hydrodynamic effect and motion response of the underwater helicopter near the water surface is calculated.The effects of different depth and speed on the six-degree-of-freedom motion response are compared and analyzed.It is concluded that the wave has less influence on the hydrodynamics of the autonomous underwater helicopter when the depth is 0.8m or more;the change of speed has a great influence on the pitch and surge motion amplitude of the autonomous underwater helicopter in head sea.Experiments were carried out in a large cross-section wave-current water tank to measure the roll angle response of the autonomous underwater helicopter in waves,and the results were compared with those of the roll numerical simulation with damping calculation,which verified the reliability of the calculation.At the same time,the hydrodynamic interaction of the autonomous underwater helicopter due to the existence of the scientific mother ship in the near-water surface is calculated and analyzed.Since the shape of the autonomous underwater helicopter is small relative to the scientific research mother ship,the radiation disturbance velocity potential of the scientific mother ship has a great influence on the hydrodynamic performance of the autonomous underwater helicopter.The autonomous underwater helicopter with relatively small scales will be disturbed due to the change of the flow field.This paper analyzes the hydrodynamic interaction of the autonomous underwater helicopters during the deployment of the ship and the stern through the scientific research ship.It is concluded that the underwater helicopter is selected as the underwater helicopter within 1.5 m to 2m from the side of the mother ship and lm to 3m from the stern of mother ship.Combined with the sea conditions of the South China Sea,the motion response under different sea conditions is calculated and analyzed.The wave data of South China Sea are fitted by Weibull distribution,and the motion responses under different sea eonditions are caleulated and analyzed.It is eoncluded that the underwater helicopter can be recovered by deploying the mother ship of the scientific research under the sea condition of grade 4 has higher safety.The comprehensive hydrodynamie foreeast data can provide a reference for the safety factor of the underwater helicopter when it is used for actual deployment and recovery operations.