Analysis of the Armoring Effect to Mixed-Grain Sediment Discharge
Date Issued
2007
Date
2007
Author(s)
Wu, Zong-Yu
DOI
zh-TW
Abstract
This study used mixed-grain as the materials to do sediment transport flume experiment and observed the motion of sediment in the process of the experiment. We could find that mixed-grain in the channel-bed was occurred different sorting or hiding phenomenon in the different flow discharges.
Because the difference caused by hiding phenomenon during experiment haven’t been further discovered in the experiment of sediment discharge, therefore we proceed channel experiments in this study, collect experimental data of existing study, add the number of combination of sediment sizes and flow discharge, and expand experimental data boundary. Besides, we record the transformation of sediment discharge as time passes to discover the time of rapid increase and the difference between before and after the time in sediment discharge to assay operating model of hiding phenomenon.
In order to analyze hiding phenomenon caused by mixed-grain, this study use stochastic type model of sediment discharge proposed by Einstein in 1950.To analyze with using dimensionless sediment transport discharge parameter and dimensionless flow parameter ψ.
This research also compared with Shields’ Diagram which is deterministic. Two turning points are found. One of them are
ψ =18.07, and Boundary Reynolds number .Another turning point is ψ =2.78, ， .Therefore, these two the turning points located on the curve of Shields’ Diagram can divine the process of sediment discharge into three sections. Such as when ψ >18.07, it means small flow discharge can’t motivate the moment of particles of bed material with little scouting toward particles on the river bed ,low sediment discharge is found in both homogenous and mixed-grain. With the increasing of flow discharge as 18.07 >ψ > 2.78,particles on river bed start sorting. Armoring layers are caused by bigger particles to form hiding phenomenon and prevent sediment discharge of smaller particles. Till flow discharge is rapid enough to motivate the moment of bigger particles when 2.78 > ψ, sediment discharge increases rapidly. And the connections of each section all appearances turning ,which tells sediment discharge shows different relationships with flow discharge between each different section because of the influence of mixed-grain sediment distribution in different flow discharge sections.
In order to find out the equation between sediment discharge and flow discharge, Einstein’s dimensionless parameters are adopted and D50 is used as the character grain parameter of sediment particles. Totally 828 sets of experimental data including 798 which have been collected from the literature reviews with adding 30 which have been done in this research are taken to process the multiple regression analysis. The models for sediment transport which is listed below can be found.
By Comparing to each everyone of those other models for sediment transport, the model derived by this research matches with the model of Meng-Chyung Shieh because both models consider standard deviation of particle grained distribution（σ）.But also the Stochastic point of view is taken to consider the effects to sediment discharge caused by the possibility of sediment motivation. To process the analysis according to Einstein’s dimensionless parameters, the results match with Einstein’s. Besides, the moment of sediment particles in bed material load is divined into different sections by dimensionless flow discharge. It can be found that hiding phenomenon and different sorting caused by flow to different grain sizes of sediment particles cause the effects toward sediment discharge.
Subjects
混合粒徑
渠槽試驗
輸砂量
遮蔽效應
序率
Mixed Grain Size
Flume Experiment
Sediment Discharge
Hiding Phenomenon
Stochastic
Type
thesis
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