To conduct inspections in water-way tunnels of hydroelectric power plants, staff usually walk through the tunnel after discharging the water. However, this takes labor and time, and the losses through the generation outage due to the cut-off of the water supply are also considerable. Therefore, we developed a floating device equipped with video cameras. It takes videos of all around the walls, including underwater, without having to discharge the water. It does not require manual operation, and is much safer than the usual inspection method.

To take clear videos, the most important factor is to stabilize the posture (direction) of the device floated down the water-way, because it is easily rotated due to turbulence flow caused by changes in the cross-sectional shape and the surface friction. We focused on the difference in the flow velocity in a cross-section of the water-way. In order to use these hydraulic characteristics, we introduced a Parachute Anchor and Stabilizer Tail for the posture control mechanism. Thanks to this simple control mechanism, there is no need for difficult settings or operation, and no risk of electrical trouble.

It is possible to output a development diagram of all around the walls via pattern matching and image synthesizing. Deformation can be easily detected, so it is possible to extend the intervals between waterway tunnel inspections that include water discharge. As a result, we expect a reduction in losses through generation outages caused by inspections, a reduction in staff burdens and much greater safety during unplanned inspections after a disaster.

1. Introduction

Tunnel structures become deformed or cracked due to ground pressure or deterioration of support members, even after completion. If these deformations become large, the wall may peel or fall off. This can cause serious accidents in road and railway tunnels and overflows in water-way tunnels due to water-way blockage. For this reason, maintenance managers need to understand the soundness of the tunnel structure and strive to maintain performance and prevent accidents.

To conduct inspections in a water-way tunnel, staff usually walk through the tunnel after discharging the water. Since the water supply cut-off period last several days including the charge-and-drain time, frequent water-way tunnel inspections are inadvisable from an economic loss perspective. In order to reduce economic losses, it is necessary to establish an efficient inspection method through technological development.

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