| Summary: | 碩士 === 逢甲大學 === 水利工程與資源保育研究所 === 97 === When water flows through the hydraulic structures like consolidation works etc., in the reach of free overfall caused by drop between upstream and downstream, the potential energy will be converted to kinetic energy. If the reach downstream of hydraulic structure doesn’t set up any energy dissipation installations, the flow will strike the riverbed directly, erode the downstream reach seriously, and threaten its security.
This research conducts a series of free overfall experiments under steady and clear water conditions for energy dissipation installations with various drop heights. This study sets up the non-disturbing pressure systems along downstream channel bottom to measure the longitudinal distribution of pressure head by pressure transducer. The impact force of flow, the rate of energy reduction and the effectiveness of energy dissipation installations are discussed. In view of energy dissipation, the impact force on riverbed with energy dissipators is lower than that without energy dissipators, indicating obvious effect of energy dissipation by installing the energy dissipators. The water cushion is formed after the installation of energy dissipators, which will make the current hits mutually in the stilling basin due to cushion effect, and reduce the flow energy.
In view of the energy reduction rate, the average maximum energy reduction is about 11% to 24% under different unit flow discharges. The experimental results indicated that the height (h) and length (L) of the stilling basin appear to be proportional to the rate of energy reduction (λE). In addition, the flow impact position ( ), and the flow depth in the stilling basin (Yp) are proportional to the drop number (D), and the flow nappe impact angle (θ) is inversely proportional to D.
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