The maximum ocean depth so far reported is about 11 000 m, and is located in the Mariana Trench in the Western Pacific Ocean. The hybrid unmanned underwater vehicle, Haidou, is developed to perform scientific survey at the deepest parts of the Earth oceans. For vehicles working at the full-ocean depth, acoustic positioning is the most effective and popular method. The 11 000 m class acoustic positioning system is relatively massive and complex, and it requires specialized research vessels equipped with compatible acoustic instruments. As a compact testbed platform, it is impractical for Haidou to carry an LBL/USBL beacon with its large volume and weight. During the descent to about 11 000 m, horizontal drift could not be eliminated because of the hydrodynamics and uncertain ocean currents in the sea trials. The maximum depth recorded by Haidou is 10 905 m, and determining the precise location of the deepest point is challenging. With the bathymetric map produced by a multibeam sonar, the terrain contour matching (TERCOM) method is adopted for terrain matching localization. TERCOM is stable in providing an accurate position because of its insensitivity to the initial position errors. The final matching results show the best estimate of location in the reference terrain map.

Underwater Gliders have found broad applications in ocean sampling. In this paper, the nonlinear dynamic model of the glider developed by the Shenyang Institute of Automation, Chinese Academy of Sciences, is established. Based on this model, we solve for the parameters that characterize steady state spiraling motions of the glider. A set of nonlinear equations are simplified so that a recursive algorithm can be used to find the solutions.

A wheel-propeller-leg integrated amphibious robot with multi-modes motion is presented as a new type of robot, which can both crawl on land and swim underwater in certain depth. The performance of swimming with the mixed thrusters composed of wheel-propellers and legs shows its propulsive capability when the robot swims in water. Based on analysis of propulsive principle of the wheel-propeller and the leg, hydrodynamic characters of the mixed thrusters are calculated, and the approximate models for propulsion of the wheel-propeller and leg are obtained according to computational calculation and simulation with commercial software. Considering the feature of energy-taking by itself, the optimal distribution of propulsion based on the wheel-propeller-leg mixed thrusters with the maximal navigational distance is studied using multi-objective optimization theory. As a result, the optimized driving parameters for the mixed thrusters are achieved to bring the maximal propulsion while consuming the minimal energy. Experiments carried out in the pool prove the validity and rationality of the optimization results.