Research On Motion Control And Underwater Docking Technology For Hybrid Underwater Glider

The development of a novel type of hybrid underwater glider (HUG) that combines the advantages of buoyancy-driven gliders and propeller-driven autonomous underwater vehicles has recently received considerable interest. However, few studies have considered a hybrid glider with docking capability, which would expand the glider’s applications. This dissertation aims to design a hybrid underwater glider for realizing underwater docking, and study the dynamic modeling, motion control and docking guidance algorithms of the hybrid glider.This dissertation first presents a novel type of hybrid underwater glider with a rotatable thruster for realizing underwater docking, which is called ZJU-HUG. A tailored dynamic model of the hybrid glider is derived. In the modeling process, a more accurate modeling method for the oil-bladder-type ballast system is given, which describes the effects of the ballast system on the center-of-gravity and the net weight of the vehicle more accurately.Based on the dynamic model of the HUG, the more accurate modeling method for the ballast system is compared with the conventional modeling method by simulations. The comparison results show that the proposed method is more accurate than the conventional modeling method, and results in better motion prediction. Besides, by the method of simulation, the performance of horizontal flight and turning motion are evaluated, and the wings level flight motion is analyzed.In the aspect of motion control, the fuzzy-PID control scheme is chose for the heading control of the HUG With regard to the flight path control, based on a feedforward/feedback control system, a method to estimate the feedforward commands and the glide path angle is proposed. The method decreases the computational complexity, and has higher control precision of the glide path angle than conventional methods.Considering that the ocean current may have a significant impact on the HUG, which is an underactuated vehicle, this dissertation presents a docking scheme with a rotatable dock. On the basis of the rotatable dock, a pursuit guidance algorithm with current compensation is given. Considering both the influence of the current and the sensor viewing volume, the method can compensate the current while locating the docking station in the sensor viewing volume, and thus increase the robustness of docking algorithm.For the convenience of experiments, we design a smaller HUG similar to ZJU-HUG as an experimental model. The smaller HUG, known as Mini-HUG, is used for model and algorithm validation. For the Mini-HUG vehicle, the performance evaluation tests, the heading control tests, and the docking test are conducted. For ZJU-HUG, the performance evaluation tests are conducted. The experimental results indicated that the hybrid glider with a rotatable thruster has higher maneuverability and can still maintain maneuverability even at low speeds unlike conventional AUVs and hybrid gliders that use control fins to turn. Moreover, the experiments also validate the accuracy of the dynamic model, the effectiveness of the heading control laws, and the feasibility of HUG docking.