Study On Longitudinal Control For Hybrid-driven Underwater Gliders

As increasing scarcity of land resources, the ocean has been of great concern to the world which has abundant resources and its important geographical significance. So the underwater robots as the tool of ocean exploration have also been of great concerns. Hybrid-driven underwater gliders(HDUGs) is a new type of underwater robot which is a combine of the autonomous underwater vehicles(AUVs) and autonomous underwater gliders(AUGs). The AUVs with propeller work in a horizontal plane and are suitable for small range, short time observation missons, but not be suitable for a wide range, long marine environment observation missions in longitudinal plane.The underwater gliders are suitable for navigation in longitudinal plane and a wide range, long time observation missions, but because of the the underwater glider cannot directly sail in a horizontal and low speed, the underwater glider is not suitable for marine environment observation mission with large current and shallow sea area. Hybrid-driven underwater gliders is a new concept of underwater robot with both buoyancy and propeller. The gliders have the characteristics of the AUVs and underwater gliders. So the gliders can work in horizontal plane, can glide along the sawtooth path and also have strong marine environment adaptability.This thesis first introduced the work mechanism of the hybrid underwater glider and the important structure. The three types of navigation model were also introduced in detail. Its kinetic model for longitudinal plane was deduced in detail using Newton's second law, and experimental verification were conduced. This thesis adopted the method of vector mechanics, which regarded the hybrid underwater glider as a multi-point system, that had following point mass: the moving internal point mass, the variable ballast point mass, the hull mass and point mass for nonuniform hull mass distribution. The gliders had the external forces such as gravity, buoyancy. The dynamics equation of the vertical plane was estabalished with using the Newton's second theorem. And simulated experiment was conduced and the experimental results show that the dynamic model can accurately describe hybrid underwater glider motion.Hybrid-driven underwater glider is nonlinear, strong coupling, influenced by the ocean currents and its structure of dynamic model is uncertain. To confront with these problems, a nonlinear control method based on the inverse system and sliding mode control was used for the longitudinal plane. In this thesis, in order to facilitate the discussion of inverse model, the longitudinal kinetic model was transformed. Combined with the controlled object and the output of the actual system, the inverse system was deduced with the transformed longitudinal kinetic model which decouple the original system into two independent single input and single output linear subsystems. Then the sliding mode control method was used as the control method of vertical speed and pitch angle control. Simulation results show that this method not only has a good control performance, but also be robust with the external disturbance.