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Basic Research on Equivalent Sand-Grain Roughness of the Sand Waves of Small-Scale Having Three-Dimensional Configuration

三维结构小尺度砂波等效砂粒粗糙度的基础研究

基本信息

批准号：
63550378
负责人：
HAYASHI Taizo
金额：
$ 1.34万
依托单位：
Chuo University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63550378/
关键词：
Sand waves of small scale Alluvial river bed configurations of small scale Three-dimensional ripples Three-dimensional dunes Equivalent sand-grain roughness Three-dimensional sand waves of small scale 相当砂粒粗度うろこ状砂連小規模河床波の三次元性河床形状抵抗三

项目摘要

(1) Conditions of occurrence of three-dimensional sand waves of small scale have been studied by means of stability analysis of river bed. Potential flow theory is applied.The initial rate of growth in dimensionless from of three-dimensional and waves has been obtained as a function of kd with parameters 1/k, Fr and C. Here, k and 1 = wave numbers of three-dimensional sand waves in the undisturbed main flow and spanwise directions, respectively ; d = mean depth of flow : F_r= Froude number ; and C = inclination factor relative to dimensionless delay distance of sediment particle. The domain of hydraulic conditions in which three-dimensional sand waves occur more easily than two-dimensional sand waves has been examined in detail.(2) About 7,500 reliable data from laboratory flume and field experiments published by previous investigators have been analyzed to obtain the values of equivalent sand-grain roughness of alluvial channel bed. A new diagram is proposed for estimating the equivalent roughness to be formed in alluvial channels.The analysis made shows that for any energy slope of flow the equivalent roughness in the dimensionless form relative to mean particle size has a distinct maximum for tau_*' = 0.2 about in which tau_*' is dimensionless grain-roughness bed shear stress.(3) In order to grasp quantitatively the time and spatial variation of channel bed configuration of small scale at their occurrence and development stages a new method of measurement has been devised combining instrumentation by the use of laser slit-sheet illumination and computer-aided image-processing technique.

(1)通过河床稳定性分析，研究了小尺度三维沙波的发生条件。应用势流理论，得到了三维沙波的无量纲初始增长率，其为kd的函数，参数为1/k、Fr和C。其中，k和1分别为三维沙波在未扰动主流方向和翼展方向上的波数； d = 平均水深：F_r= 弗劳德数； C = 相对于沉积物颗粒无量纲延迟距离的倾斜因子。详细研究了三维砂波比二维砂波更容易出现的水力条件范围。(2)对前人发表的实验室水槽和现场实验的约7500个可靠数据进行了分析，获得了冲积河道床的等效砂粒粗糙度值。提出了一种估计冲积河道中形成的等效粗糙度的新图。分析表明，对于任何水流能量斜率，相对于平均颗粒尺寸的无量纲形式的等效粗糙度在tau_*' = 0.2左右有一个明显的最大值，其中tau_*'为无量纲颗粒-粗糙度河床剪应力。(3)定量掌握小尺度河床形态的时间和空间变化。在它们的出现和发展阶段，已经设计出一种新的测量方法，结合使用激光狭缝片照明和计算机辅助图像处理技术的仪器。