Image analysis of open-channel flow with sparsely distributed strip roughness in very shallow water condition accompanying three-dimensional and time-dependent large surface deformations

摘要

An open channel flow with strip roughness is a typical turbulent flow which is capable of controlling the form resistance by changing the roughness spacing. Although most of the experiments have been conducted for a flow depth much greater than the roughness height, flow features under shallow flow conditions are not investigated in detail. Therefore, attention was paid to relatively shallow flows with a depth several times the roughness height and a relatively large roughness spacing. The water surface was found to exhibit various features under different hydraulic conditions, e.g. the surface pattern changes its mode from two to three dimensional configurations and, in an extreme case, a hydraulic jump produced in between roughness elements oscillates periodically. In order to investigate such complicated flow features, a new image processing technique was developed to extract water surface patterns and the mechanism of oscillation was elucidated.