水工結構設計對減少排放水體表面浮泡量之探討

Abstract

為有效減緩排放渠道因跌水造成的水體表面浮泡生成，本研究以1：16縮尺渠槽進行試驗，量測浮泡濃度與表面浮泡體積，期望透過水工結構消能以減少水體夾氣量的生成。為了量化水體流經各種水工結構後的浮泡量並比較各模型的適用性，本研究自製夾氣量測儀器來計算水體中的氣泡濃度。首先，透過空氣供應率及氣泡上升時間來確定標準氣泡濃度，接著使用設計的雙通道量測水體電壓及電流，利用文獻中的公式計算氣泡濃度，並以標準氣泡濃度檢驗其準確性。浮泡體積則採用兩種方式進行量測：(1) 透過Agisoft Metashape及ArcGIS進行建模和影像處理；(2) 使用ImageJ進行影像分析。結合氣泡濃度與浮泡體積，以得出實際的浮泡量，本研究以此作為標準，選定最佳的水工結構設計。 在縮尺試驗中，本研究於渠槽上游的蓄水道設置曝氣管線，並使用三馬力及一馬力的空壓馬達作為空氣供應，藉此增加水體擾動曝氣，以促進水體浮泡生成。三組試驗平台分別安裝於V型堰上游處、第一及第二跌水堰之間、尾水板前，以測量實驗數據，藉此比較不同模型在相同點位所產生的浮泡量。試驗水體以300mL界面活性劑作為輸入量進行縮尺試驗。試驗前置工作包括設置尺規供建模使用及浮泡濃度探針的伸縮桿等工項。本研究使用Agisoft Metashape和ImageJ來計算浮泡體積，兩者結果非常接近，推論兩種浮泡體積量測方法具有一致性。最後，透過實際浮泡量的計算進行增幅比例的比較，得出最佳水工結構設計能顯著降低浮泡增幅。

To effectively reduce the formation of surface bubbles in discharge channels caused by waterfalls, this study designed nine discharge channel models and conducted experimental measurements of bubble concentration and surface bubble volume using a 1:16 scale flume. The goal was to mitigate the entrained air in the water through energy dissipation in the hydraulic structures. To quantify the bubble volume in the water passing through each hydraulic structure and compare the applicability of each model, this study used a self-made entrained air measurement instrument to calculate bubble concentration. First, standard bubble concentration was confirmed through air supply rate and bubble rise time. Then, a dual-channel system was used to measure the voltage and electric current of the water, and bubble concentration was calculated using a formula from the literature and verified against the standard bubble concentration. Bubble volume was measured using two methods: (1) modeling and image processing with Agisoft Metashape and ArcGIS. (2) image analysis with ImageJ. Combining bubble concentration and bubble volume, the actual bubble volume was determined, which served as the standard for selecting the best hydraulic structure design. In the small-scale experiment, aeration lines were installed in the upstream reservoir of the flume, using three-horsepower and one-horsepower air pumps to supply air and increase water disturbance to enhance bubble generation. Three sets of test platforms were installed upstream of the V-shaped weir, between the first and second drop structure's weirs, and before the end of the channel to measure experimental data. This setup allowed comparison of bubble volume at the same points for different models. The experimental water used was a formulation with 300 mL of surfactant as the input volume. Preliminary tasks included setting up rulers for modeling and adjustable arms for bubble concentration probes. In this study, the volume of surface bubbles at the second measurement point of Model 3 was calculated using Agisoft Metashape and ImageJ. Since the two values were very close, it was inferred that the bubble volume measurements obtained from the two methods were similar. Furthermore, by comparing the actual bubble volume increase ratios between the first and third measurement points across nine different models, Model 2 was found to have the lowest increase in bubble volume. Thus, Model 2 is identified as the best hydraulic structure design.