Analysis of the Propulsion Efficiency of Buoyancy-driven Underwater Gliders

As a new type of autonomous underwater vehicle, the underwater glider has many advantages such as long endurance, high propulsion efficiency, and low self-noise due to the application of buoyancy-driven technology.It has promising applications in the oceanographic survey and ocean exploration.The propulsion energy when the underwater glider dives and ascends with a constant velocity is analyzed.The propulsion efficiency is then defined on the basis of this analysis and the calculation methods are derived with and without consideration of the extra energy losses.Investigation is also conducted to figure out factors that influence the efficiency and methods for improving the efficiency.The lift-to-drag ratio of wings and the extra energy losses are found to be the main factors influencing the propulsion efficiency and the lift-to-drag ratio of wings is the most important factor.In order to reveal the relationships between the propulsion efficiency and the structure parameters and the forms of the glider wings, the effect of the aspect ratio and the sweep angle of wings on the lift-to-drag ratio are investigated by using an empirical equation, and the lift-to-drag ratio of wings with same area but different forms are also calculated by using computational fluid dynamics software Fluent 6.2.The results provide an insight into the underwater glider design.