Three-dimensional Measurement of Developing Sand Waves and Estimation of Wave Height.

点击翻译按钮获取中文摘要

Flow resistance in alluvial channels is closely related to bed configurations. In this research project, two of experimental studies were made of the relation between bed configurations and flow structures. The main conclusion obtained through the experimental studies was that the increment of height of sand waves was caused by slant vortices.(1) The developing process of sand waves were investigated by three-dimensional measurements of bed configurations. The measurements were made by three supersonic bed-elevation meters on the flow in the straight channel 18m long and 1m wide. The data obtained were processed by a computer and contours of bed configurations were displayed in graphical outputs. Using the results, skewness factor of bed elevation, spacial distributions of cross-correlation coefficients between two of the longitudinal distributions of bed elevation with small time difference, propagating velocity of sand waves and spacial distribution of local erosion and increment of wave hight were calculated. Cosequently, it was found that the development of sand waves was closely related to slant vortices, which appeared in the downstream side of sand waves and caused local scour.(2) Measurement were made on the three-dimensional structure of the flow over sand waves using flow visualization. The experiments were conducted in the straight channel 8m long and 40cm wide. Stereographs of the top view of the flow and pictures of flows in longitudinal closs-sections were taken by fixed cameras or moving cameras. The mechanism of slant vortices were clarified by the measurements.