| 摘要: |
| 以流速为主要参变量,在长度为339.3m的往复式直水槽中进行细颗粒泥沙絮凝沉降试验,试验得到了垂线平均含沙量、絮凝现象、垂线含沙量梯度、泥沙粒度四方面的沿程变化规律。通过对以上四方面变化分析,细颗粒泥沙动水絮凝沉降的基本特性是:动水絮凝沉降速率和沉降量受碰撞絮凝概率与剪切破碎概率、絮凝体所受外力与本身抗力两大关系的制约,而流速又通过制约以上两大因素的变化,成为制约絮凝沉降速率和沉降量的主要因素。 |
| 关键词: 细颗粒泥沙 絮凝 动水沉降 流速 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金资助项目,49976023号 |
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| A FLUME EXPERIMENT ON FLOCCULATION SETTLING OF FINE-GRAINED SEDIMENT IN MOVING WATER |
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ZHOU Hai1,2, RUAN Wen-Jie3, JIANG Guo-Jun3, YAO Sheng-Chu3, ZHANG Zhi-Zhong3
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1.Transportation College of Hohai University,Nanjing,210098;2.Shanghai Institute of Waterways,Shanghai,200120;3.Institute of Harbor,Coastal and Offshore Engineering of Zhejiang University,Hangzhou,310028
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| Abstract: |
| Demanded by the waterway engineering in Changjiang (Yangtze) River estuary region, an experiment on the flocculation settling of fine-grained sediment in moving water was simulated in a flume system. The flume, 339.3m-long straight with a fixed slope was specially designed earlier. The experiment was conducted for comparison among cases of moving water in different sediment concentrations, flow speeds, and salinities for understanding the mechanisms of flocculation by grain collision and de-flocculation by shearing force of flowing water. Photoelectric observation was made at 6 horizontal positions and 6 vertical layers (at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 of the water depth) in of the water in the flume. The test parameters were: 5 kg/m3 in concentration, 26°C, 25cm water depth, and the speed at 6, 16, 30 and 40 cm/s. Salinity was set at 0 and 10. The sediments were collected in the estuary sized between 0-32 μm, washed and cleaned.
Results show that (1) in case of identical current velocity, the average sediment concentration at vertical direction decreased exponentially along the distance of running, and the sediment settlement rate decreased with slowdown flowing. (2) the size and amount of flocs decreased with the distance at the same flow speed, whereas flocculation reduced when water running faster. At 40 cm/s, no flocculation could be observed. (3) the sediment concentration boosted at 0.8-1.0 of the water depth in strong flocculation condition.
Flocculation and de-flocculation were alternated depending on the balance in possibility between grain collision/fluid shearing forces, and the floc-joining/?oc-break-up forces. In the process, flow speed was proved to be a major factor. |
| Key words: Fine-grained sediment, Flocculation, Settling in moving water, Current velocity |
