Semi-Physical Simulation of AUV Homing and Docking Processes

Existing simulation systems ignore the ocean current interference, so that the real-time motion state of the model can't be directly reflected. To solve the problem, a semi-physical simulation system based on 3D visual scene is designed to directly display the motion states of the AUV (autonomous underwater vehicle) during the homing process and the recovery process through docking like a helicopter landing. The AUV and the underwater terrain are modeled using Multigen Creator software. The visual simulation is realized by calling the simulation interface library functions of Vega software in Visual C++. For motion control, a global path planning method for homing is designed based on B-spline theory, and a global path satisfying underactuation constraints is searched by genetic algorithm. A path tracking controller is designed by the layered structure of guidance control and executive control, in which the PID (proportional-integral-differential) guidance law can adjust the reference attitude angle according to the ocean current information, and the S-plane control law can make stable, fast and accurate response to the status information and the reference attitude angle. All the processes are simulated on the test platform, including the AUV starting from the release position, autonomously homing by tracking the calculated global path, till docking. The results show that the influence of ocean current on the path tracking deviation of AUV is small in homing process, but its influence in docking process is very large when the relative angle between the ocean current and the heading direction is big, which maybe cause a recovery failure. A reasonable homing path can be planned for AUV to complete the recovery process under the influence of ocean current, and all the processes can be directly reflected in real-time in the designed semi-physical simulation system.