Study on Unequilibrium Sediment Transport Rate and Local Scour around Structures

主要研究了以下三个方面的内容：1）波浪作用下底床地形变化引起的不平衡输沙动滚：从理论上分析了沙床的稳定性。结果表明，输沙率的不均匀性虽使床面失稳，但输沙的不平衡性和步长的分散性是单一优势长度的存在所必需的。2）薄层水流输沙率：利用U形管对薄层水流输沙现象进行了一系列实验研究。实测了输沙率、泥沙运动和流速分布。得出了输沙率与床面切应力的1.5次方关系。本文还讨论了薄层流区的极限。3）波浪作用下圆柱周围的局部冲刷：在波浪水槽中进行了一系列的试验。将观测到的冲刷形态分为两类。在考虑水流与床面相互作用的基础上，对冲刷机理进行了探讨。通过流动显示技术证实了脱落涡的滚动。

Following three items were studied.1) Dynamic roll of nonequilibrium of sediment transport on bottom topography change under the wave action: The stability of sand bed was analysed theoretically. It was confirmed that the nonequilibrium of sand transport and scattering of step length are necessary for existance of single dominant length of bottom topograpy although asymmetry of sand transport rate make the bed unstable. The results were reported in the first reference.2) Sediment transport rate in sheet flow regime: A series of experiment on sediment transport phenomena were carried out in sheet flow regime using an U-shape tube. Sediment transport rate, sediment motion and velocity distributions were measured. The 1.5 power relationship between transport rate and the bed shear stress was concluded. The limit of sheet flow regim was also discussed. The results were reported in the second reference.3) Local scour around a cylinder under the wave action: A series of experiments were performed in a wave tank. The observed shapes of scour were classified into two category. The mechanism of scour was discussed considering the interaction of the flow and the bed. The roll of shedded vortices was confirmed through the flow visualization technique.