渠道潰壩實驗之潰口形狀與流速斷面影像分析

Cross-sectional imaging of channel shape and flow velocity in half-channel dam breach experiments

陳睿珣(Jui-Hsun Chen)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202100876

摘要

在潰壩實驗中，觀測自由水面下渠道幾何變化及流速是相當困難但有意義的，為了達成這個目標，本論文發展出一套方法應用在水工模型之潰壩實驗。
為了能觀察水面下的變化，實驗採用半渠道形狀，側邊為透明壓克力，再用雷射光照亮沿著潰壩渠道的三個斷面。這些斷面可以觀測潰壩過程中沖蝕的形狀演變。也可用來追蹤粒子在斷面彼此間的位置及量測流速。
同時，觀測形狀變化與流速的測量方法可運用在計算潰壩流量，並為此設計出兩種實驗模型，分別是固定壩與土砂壩，先用前者於穩定流的條件測試方法，後者期望能應用此方法來觀測潰壩渠道的變化。採用手動影像處理的方法，能成功測量形狀變化與流速，並估計出相對應的流量。在前者固定霸實驗中，計算出的流量結果與實驗室量測流量值達合理的吻合。實驗中也仍嘗試採用自動估算的方式，然而結果穩定性不足，仍有問題得克服，固最後未予以採用，仍以手動為主。

關鍵字

潰壩實驗 ； 斷面測量 ； 斷面流速 ； 雷射掃描 ； 水工試驗模型

並列摘要

In dam breach experiments, it is often desirable but difficult to monitor the channel geometry and flow velocity below the water free surface. To achieve this goal, this thesis develops and tests a new approach applicable to laboratory experiments. To gain visual access, the experiments are conducted in a half-channel configuration, with a transparent sidewall taken as a symmetry plane. Next, laser light sheets are used to illuminate three transverse cross-sections along the breaching half-channel. These cross-sections make it possible to monitor the evolving shape of the erodible channel. They also allow the tracking of tracer particles from one cross-section to the next, hence measurements of flow velocity within the channel.
Together, the shape and velocity measurements can be used to estimate the water discharge through the breach. Two sets of experiments are conducted. Rigid dam experiments are first used to test the approach for steady flow conditions. Next, loose dam experiments are pursued to apply the approach to evolving breaching channels. Using manual image processing methods, it is found possible to measure both shape and velocity, and to estimate the corresponding discharge. For the steady rigid dam experiments, the resulting estimates are found to be in reasonable agreement with outflow measurements. Automated algorithms to capture and process particle tracks are also proposed, but problems remain to be solved before these algorithms can be used with confidence.

並列關鍵字

dam breach experiment ； cross-section measurement ； cross-section velocity field ； laser scan ； hydraulic test model

參考文獻

ASCE EWRI Task Comm Dam. (2011) Earthen Embankment Breaching. Journal of Hydraulic Engineering, 137(12), 1549-1564.

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Chen, I.-H. (2013) Twin laser sheets scanning of 3D velocity fields in steady open channel flow experiments. MSc thesis, National Taiwan University.

Coleman, S., Andrews, D., Webby, M. (2002) Overtopping breaching of noncohesive homogeneous embankments. Journal of Hydraulic Engineering-ASCE, 128(9), 829-838.