| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 96 === There are two types of the resistances of the vegetation: submerged and unsumberged. This study focuses on the submerged type to investigate the influence of different vegetated density on the vegetation resistance, the variation of velocity, and the variation of drag coefficient, Darcy-Weisbach factor, and Manning’s n. The cylinder is used as the model plant. This study changes the effects of lateral spacing and longitudinal spacing, discussing the different of the flow rate.
Because the flow is affected by the vegetation, the flow field changes rapidly. If the traditional single-point measurement at a time is adopted in the experiment, the variation of the velocity field in the vegetated channel cannot be obtained completely and effectively. Hence, this study adopts non-intrusive color particle image velocimety (CPIV) to measure the vertical 2-D flow field in the vegetated channel. The CPIV method uses Argun laser as the light source, the PCAOM separates the light into blue and green lights and they form a light sheet after emitting on a rotating eight-side mirror, the CCD takes the instantaneous images of vegetated-channel flow field, and then obtains the velocity field through the set-up of interrogation window and image analysis Except the CPIV, the study makes a moving platform (Yo-Ta Chen, 2008) that is connected force gauge, act as water and flow through this platform, vegetation it influences to be dilatory, force gauge read value (N) at the platform. The result is exported by the computer, examine the resistance of the vegetation directly.
After measuring the vegetated-channel flow field with the CPIV method, the vegetation resistance can be calculated and be compared with the value of the measured (Yo-Ta Chen, 2008). The results demonstrate that flow resistance is greatly influenced by both depth and velocity but that the effects are opposite in sign. The drag coefficient increases in only a slightly nonlinear fashion with the relative density ratio (total vegetation stomatal area/bed cross sectional area), but Darcy-Weisbach factor increases in a highly nonlinear manner with increasing the relative density ratio, so does Manning,s n. Expect there are effects of the lateral spacing of the vegetation, the longitudinal spacing of the vegetation can also influence it. The less longitudinal spacing is, the bigger roughness of the vegetation is.
Keywords: vegetation, CPIV, vegetation resistance
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