Abstract: The current autonomous underwater vehicle(AUV) cannot meet the requirement of long time ocean environment measurement owing to the limitation of the onboard electric power. In order to reduce the power consumption effectively to solve the problem of AUV’s working time being too short, a small buoyancy changing AUV with the capacity of soft landing and bottom-sitting is developed. This AUV can realize the function of measuring at fixed point by landing and sitting on the seafloor, so it can carry out long time ocean environment measurement with the limited power. Based on this, the landing strategies of AUV are discussed. Based on the discussion of the landing strategy of free fall with water injection, the relationships between the landing velocity, landing time, landing pitch angle and the injected water volume are analyzed. Finally, the strategy of landing with controlled water injection is selected. Then landing controller based on fuzzy control is designed. In this method the injected water volume is adjusted by fuzzy inferences according to the distance to the seafloor and the pitch angle of AUV. This can guarantee that AUV will land on the seafloor in shorter time. At the same time, the landing velocity and the landing pitch angle can be kept in a very small range. This can meet the requirement for AUV to land on the seafloor safely. The feasibility of this strategy has been verified by the results of simulations and sea experiments.

Key words: Autonomous underwater vehicle, Fuzzy control, Landing, Water injection