Study on Unequilibrium Sediment Transport Rate and Local Scour around Structures

研究了以下三个项目。1)波浪作用下海底地形变化对输沙不平衡的动力翻滚：从理论上分析了沙床的稳定性。虽然输沙速率的不对称导致了床层的不稳定，但输沙的不平衡和步长的散射是形成单一优势长度的必要条件。结果在第一篇参考文献中报道。2)板流输沙速率：采用u型管对板流输沙现象进行了一系列实验研究。测量了输沙速率、泥沙运动和流速分布。得到了输运速率与床层剪应力的1.5次幂关系。讨论了薄板流态的极限。结果在第二篇参考文献中报道。3)波浪作用下圆筒周围局部冲刷：在波浪槽中进行了一系列试验。将观测到的冲刷形态分为两类。考虑水流与床层的相互作用，讨论了冲刷机理。通过流动显示技术，确定了脱落涡的卷形。

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.