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

冲积河道的流阻与河床形态密切相关。本课题对床层形态与流动结构的关系进行了两次实验研究。通过实验研究得出的主要结论是，沙波高度的增加是由斜涡引起的。(1)通过对河床形态的三维测量，研究了沙波的发展过程。用3台超音速床层高程仪对长18m、宽1m的直流道内的水流进行了测量。所得数据经计算机处理后，以图形输出方式显示床型轮廓。在此基础上，计算了床面高程偏度因子、床面高程纵向两种小时差分布间相互相关系数的空间分布、沙波传播速度以及局部侵蚀和波高增量的空间分布。结果发现，沙波的发展与斜涡密切相关，斜涡出现在沙波下游，造成局部冲刷。(2)利用流场可视化技术对沙波流场的三维结构进行了测量。实验在长8m，宽40cm的直道中进行。通过固定摄像机或移动摄像机拍摄了流动的俯视图和纵向截面的流动图像。通过测量，阐明了斜涡的形成机理。

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.