| Summary: | 碩士 === 逢甲大學 === 水利工程與資源保育研究所 === 98 === Taiwan’s rivers are characterized with steep terrain, narrow and small watershed, rapid-varying flow velocity, and large fluctuation in discharge between dry and wet periods. Sediment delivery by these rivers can increase many folds following floods of torrential rains or typhoon events. The sediment transport phenomena have caused severe erosion and sediment deposition in downstream channels and directly impact flow regimes, construction and maintenance of hydraulic structures, channel migrations, and the ability to manage these rivers. To apply science-based approach to solve these problems, it is necessary to understand the characteristics of sediment transport; and long-term observed sediment data are essential. With these needs, we consider a technique that can monitoring suspended sediment concentration (SSC) with such capabilities as being precise, instantaneous, on-line, and continuous to be of high priority on the research agenda.
The tube sensor of vibration is a technique for measuring SSC in turbid water, and the measurement has been conducted by passing turbid-fluid through the tube. This research examined the feasibility of measuring SSC in passing the tube externally. It is anticipated that this approach can minimize the issue of sediment deposition in the tube when turbid water passes through the vibrating tube. Based on the principle of acoustic vibration, a new monitoring method for instantaneous fluid density is proposed and verified with experiments. With the boundary of the vibrating tube subject to the flow loading of the passing water, the acoustic vibration principle predicts changes in the resonance frequencies of the tube. Therefore the physics and the mechanism controlling the vibration frequency and fluid density are still in need of research.
The experiments developed a simple-base and a cantilever vibrating tube mounting systems to measure the resonance frequencies of the vibrating tube. Turbid fluids of different density were used in the experiments. The results indicated that resonance cycles of the tube correspond to changes in resonance frequencies subjecting to fluids of different density nicely. The sensitivity of the measured change in resonance frequencies can adequately differentiate the densities of the fluid. Hence the vibrating tube sensor can have great potential in measuring fluid density in different industrial domains as well as SSC in natural river environments.
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