| Summary: | 碩士 === 逢甲大學 === 土木及水利工程所 === 92 === Streamflow measurements for the medium and high flows are difficult in Taiwan due to the geographical reasons. These data, however, are very important for the river regulation and water resources planning and design. The flows in the natural rivers are usually unsteady during the medium and high flow periods. In order to obtain these data more efficiently, it is necessary to simplify the measuring techniques based on the theory.
The Fiber-optic Laser Doppler Velocimetry (FLDV) was adopted in this experimental study to investigate the characteristics of the steep open channel flow over a rough boundary, which were formed by gluing a layer of uniform 8 mm glass particles on the channel bottom. The experiments aimed at searching into the dissimilarities of the characteristics of the steep open channel flows over rough and smooth boundaries wide different channel widths. And both the influences of channel bed slope and aspect ratio (ratio of channel width to depth) on mean velocity profiles are investigated.
In this study, the flow parameters including channel bed slope, aspect ratio and the location of measuring vertical affect the mean velocity profiles in a cross-section. The mean velocity profiles can not be expressed with a two-dimensional model. The maximum point velocity occurring below the water surface is an indication of three-dimensional flow. Thus both the magnitude and location of the cross-sectional maximum velocity are important indices influencing the pattern of velocity profiles in the whole cross-section.
In addition, the results of comparing with three kinds of velocity estimation were very well. In contras with convenience, the proposed method, where only the maximum surface velocity( )at Y-axis(vertical passing through the maximum point velocity of the cross section)need to be measured. The flow discharge( ) was then computed by multiplying the estimated flow area( ) with mean velocity ,which has the advantages of short operation time and high accuracy. The results of this study can be used as a basis of the high efficient flow discharge measurement, which can estimate the medium and high flow quickly and effectively.
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