1991 Fiscal Year Final Research Report Summary
Reinvestigation of Sediment Transport Mechanism due to Wave Action from the Viewpoint of Fluid Mechanics
| Project/Area Number |
01460180
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | Saitama University |
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Principal Investigator |
HORIKAWA Kiyoshi Saitama University, Department of Foundation Engineering, Professor, 工学部, 教授 (10010571)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Hiroaki Saitama University, Department of Foundation Engineering, Research Associate, 工学部, 助手 (20008832)
ASAEDA Takashi Saitama University, Department of Foundation Engineering, Associate Professor, 工学部, 助教授 (40134332)
IKEDA Syunsuke Tokyo Institute of Technology, Department of Civil Engineering, Professor, 工学部, 教授 (60016590)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Oscillatory Boundary Layer Flow / Sand Ripples / Organized Vortex / Vorticity / Vortex Formation / Vortex Disappearance / 2-D LDV / Turbulence Intensity |
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| Research Abstract |
The aim of the present research project is (1) to review carefully a great number of research papprs presented so far in relation to sediment transport mechanism due to wave action, and (2) to carry out a series of laboratory investigation on oscillatory boundary flow over ripple models. The basic concept of this research project is reexamine the mechanism of sediment motion induced by time-dependent fluid motion through the view of fluid dynamics. In order to clarify the interaction of the fluid motion and the sediment particle motion, two types of fixed ripple models are installed separately inside an oscilla. tory flume, the size of which are nearly similar to sand ripples generated along the sea bottom by wave action. The first type has a sharpe crested form and the second a round crested form. The former has a some what different shape from the natural sand ripple, but has an advantage to simplify the flow pattern. A 2-D laser Doppler velocimeter (LDV) is effectively used to measure the flow characteristics of mean velocity, fluctuation of velocity components, turbulence intensity, Reynolds stress, and. kinematic eddy viscosity. These terms are diagrammatically shown on a raph for each phase of oscillation, through which formation and disappearance vortices can be visualized. By bomparing these data for sharpe and round crested models, it is clearly shown that the intensity of vortex formed behind a sharp crest is much stronger than that of vortex behind a round crest. In order to look at the temporal and spatial variation of vortex distribution with phase, the measured velocity records are used to calculate the vorticity at each grid point. By using the above data, the development and dissipation process of overall vortex intensity are quantitatively studied.
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