【作者】 邵凯；

【导师】 孙志林；

【作者基本信息】 浙江大学 ， 港口、海岸及近海工程， 2010， 硕士

【摘要】 天然河流的泥沙输移大多在浑水条件下进行,浑水条件与清水条件下的输沙机理存在一定差异。尤其对于较细颗粒泥沙,在研究推移质输移时,不能忽略它与悬移质的交换。鉴于问题的复杂性,迄今为止,处理推移质输移问题时考虑悬移质对其影响的研究甚少,故对此进行研究具有重要意义。本文基于近底泥沙交换三状态随机-力学模式,对浑水中非均匀推移质输移问题的研究作了初次尝试。主要在床沙与推移质交换的同时,考虑了床沙与推移质向悬移质的净交换。实质上是床沙、推移质和悬移质根据当地水流条件引起的比例再分配,趋向于泥沙交换平衡方向调整。将表征悬沙特性的扬动概率β_k引入浑水条件输沙模型的构建中,从理论上建立了浑水中非均匀推移质分级输沙率公式,进而导出总输沙率及推移质级配的计算式。分级推移质公式体现了悬移质存在对于推移质数量的减少程度,此公式对清水条件下的输沙率估算仍然适用。浑水条件下进行的推移质输移水槽试验结果和野外实测资料验证了理论公式的合理性与可靠性,并进一步探求了输沙强度和水流强度的关系。在级配研究中发现,浑水条件下推移质级配可能发生“粗移”现象,该现象在清水条件下输沙时不可能发生。结果表明:在浑水中,以悬移质形式存在的砂质泥沙含量对有效估算推移质输沙率有着不容忽视的影响。在某粒级运动泥沙总量不变的前提下,因一部分沙粒悬浮于水体中,使得推移质数量相对减少。更多还原

【Abstract】 Sediment transport in natural rivers occurs almost in sediment-laden flow. The difference may exist between mechanism of sediment transport in turbid waters and that in clear waters. Especially, it should not neglect the exchange between bedload and suspended load in fine bedload transportation. The effect of suspended load on bedload transport in turbid waters, so far, has hardly been considered becourse of its complexity. Therefore, the study on this problem is of paticular significance.It was a maiden attempt in study on nonuniform bedload transportation in sediment-laden flow. On the basis of three states exchange mode of sediment on the bed surface, the analytical method of combining stochastic theory with mechanics was used. Especially, while exchanging between bedload and bed material, the net transport of bed load towards waters was considered. As a matter of fact, the proportion of bed material, bedload and suspended load may redistribute and adjust to equilibrium exchanging according to flow intensity.Probability of suspension (β_k), which represent characteristic of suspended load, was included in the process of building sediment transportation model in turbid waters. The formulas of fractional, total nonuniform bedload transport rates and bedload size of distribution were established theoretically. Fractional bedload transport rates formula can reflect the degree of bedload reduction due to existence of suspended load, and it was also appicable to sediment transportation in clear waters.Through the flume experiment of bedload transportation in turbid waters, the rationality and reliability of the proposed formulas were verified by the experimental and field measured data. The relationship between sediment transportation intensity and flow intensity has been established. It is found that bedload graduation may coarser than that of original bed material in turbid waters in sediment graduation research, and this phenomenon is of none probability in sediment transportation under clear waters condition. The results show that to the effective estimation of the sandy bedload transport rate, it should not be neglected the content of the suspended load which comes from bedload, and the amount of bedload was relatively decreased.更多还原