Development of hovering control system for an underwater vehicle to perform core internal inspections

In this paper, a hovering control system for an underwater vehicle is proposed to support core internal inspections. The system adopted a localization part and a thruster control part. The former utilizes a map-matching method, referring cross-sectional shape data cut from a three-dimensional computer aided design (CAD) and structural shapes measured by a laser range system for horizontal positioning. A pressure sensor provides vertical positioning. The latter utilizes the thrust vector control, or reference thrust vectors are converted to each propeller thrust based on the vehicle's geometric structure. Experiments to evaluate performance of the proposed system were implemented at a mock-up of the reactor bottom part. As a result, it was confirmed that the position was detected with an accuracy of 48 mm, and for a flow velocity of 200 mm/s, it was verified that the vehicle hovered within 77 mm of a target point. Therefore, core internal inspections can be stably carried out even where there is external force caused by water convection flow.