Critical Tractive Force of Very Large Gravels on Mountainous RiverBed
Project/Area Number 
63550375

Research Category 
GrantinAid for General Scientific Research (C)

Allocation Type  Singleyear Grants 
Research Field 
Hydraulic engineering

Research Institution  The University of Tokushima 
Principal Investigator 
OKABE Takeshi The University of Tokushima, Faculty of Engineering, Associate Professor, 工学部, 助教授 (10035652)

CoInvestigator(Kenkyūbuntansha) 
YOSIDA Hiromu The University of Tokushima, Faculty of Engineering, Research Assistant, 工学部, 助手 (10210717)
NAKANO Susumu The Universtiy of Tokushima, Faculty of Engineering, Lecturer, 工学部, 講師 (50198157)

Project Period (FY) 
1988 – 1989

Project Status 
Completed (Fiscal Year 1990)

Budget Amount *help 
¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)

Keywords  Bed Load / Critical Tractive Force / Mixed Bed / Fluid Force / Incipient Motion / 流砂 / 移動限界掃流力 / 抗力・揚力 / 流体力変動 / 土砂水理学 / 移動限界 / 混合砂礫 / ピックアップレート 
Research Abstract 
In this study, at first, the characteristic of fluid force acting on three types of gravel model was investigated experimentally with respect to both the time averaged and flactuating values of the drag and lift. Secondly, the process of the escaping phenomena was considered theoretically and an equation for the critical tractive force of an isolated gravel protoruding from sediment bed with an arbitrary protrusion hight. The Summary of the Results of this Research is as Follows. (1) The velocity at the hight of the top of gravel is most pertinent as the representative velocity of the fluid force. (2) The rate of the timeaveraged value of lift to that of drag is not affected by relative depth but greatly varies with the change in protrusion rate. (3) The characteristics of drag and lift coefficients of sphere and short columns (circler and elliptical cross sections) were quantitatively clarified. (4) The probability density of the fluctuation of drag and lift is well approximated by the Gauss's normal distribution function. (5) The relation between the standard deviation of the fluid force fluctuation and the protrusion rate was also clarified quantitatively. (6) In the theoretical consideration, the behavior of a spherical gravel which rolls up a slope under the effect of turbulent flow was formulated and solved by the use of some assumptions for fluid force. (7) The deduced equation for the critical tractive force includes the pickup rate as one of the para meters, and therefore the physical meaning of the value given by the equation is distinct. (8) The Validity of the Equation was Confirmed Experimantally.

Report
(3 results)
Research Products
(5 results)