推移质非饱和输移基本规律研究

发布时间：2018-04-25 13:31

本文选题：推移质 + 悬移质　；参考：《武汉大学》2014年博士论文

【摘要】：泥沙运动是河流动力学及地貌动力学研究中的重要科学问题。然而,受到研究条件的限制,以往最初始的研究基本上都是基于均匀沙条件下的饱和平衡输沙,而泥沙非均匀性及恢复饱和过程对泥沙运动的影响机制至今仍远未清楚。最近对冲积河流过程多重时间尺度的研究,从理论上揭示了冲积河流过程推移质运动能够很快调整到饱和平衡输沙状态,而悬移质运动则需要相对较长的过程,为界定饱和平衡输沙假定的适用性提供了全新的理论基础。本文以冲积河流过程多重时间尺度的研究为理论基础,着眼于非平衡输沙过程恢复饱和机制的进一步研究。在浅水动力学理论框架下对饱和与非饱和泥沙输移数学模型进行了数值模拟比较研究。结果表明,对推移质运动,饱和输沙模型与非饱和输沙模型差异局限于进口附近非常小的范围内,从而饱和输沙模型能够近似适用。然而,由于河床变形对水流运动的反作用,要正确模拟水流要素变化应该采用非饱和模型。对悬移质运动,饱和输沙模型与非饱和输沙模型存在实质性差异,悬移质的数值模拟研究,应该采用非饱和模型。研究结果有助于促进泥沙运动数学模型的发展和合理运用。对明渠泥沙运动恢复饱和距离随水沙条件的变化规律进行了定量的研究。研究结果表明,无论上游来沙增加或者减少,恢复饱和距离随悬浮指标的变化规律是一致的,即悬浮指标加大,恢复饱和距离减小,该规律与泥沙运动模式无关,即所揭示的规律普遍适用于悬移质和推移质运动。而定量而言,推移质恢复饱和距离只是水深的几十倍,而悬移质恢复饱和距离则可能高达数百倍水深的数量级甚至更长。研究结果进一步证实推移质向平衡状态调整很快,饱和输沙模式能够近似适用,而悬移质恢复平衡过程相对较长,应该采用非饱和输沙模式；同时,对饱和输沙概念的适用性提供了定量的判据。将水沙运动数值模拟研究中的积分平均模式推广至风沙运动数值模拟研究中,在此基础上,将冲积河流过程多重时间尺度理论扩展至风沙运动。数值算例与风洞实验结果对比表明,积分平均模型能够基本准确地捕捉风沙运动输沙率变化的基本特征,而积分平均模式相对于完整三维模型,能够大大提高计算效率。风沙与水沙运动多重时间尺度比较研究表明,风沙运动与水沙运动相类似,对于推移质含沙量向挟沙力调整的相对时间尺度较小,含沙量向挟沙力调整得非常快,很快能达到饱和平衡输沙,而对于悬移质,含沙量向挟沙力调整则相对较慢。将推移质非饱和输沙基本规律研究扩展到非均匀沙情形,开展均匀沙与非均匀沙的清水冲刷试验。试验数据分析结果表明,在冲刷条件下,细沙对粗沙的输移有促进作用,而粗沙对细沙的输移有抑制作用。这种促进作用随着细沙含量的增加而增加,而抑制作用随着粗沙含量的增加而增加,同时,促进和抑制作用随着流量的减小而增大。通过对以往平衡输沙条件下非均匀沙试验结果的分析,验证了抑制与促进作用的变化趋势。研究成果对为非均匀推移质输沙率及地貌形态变化的计算供了新的理论基础,有助于新的计算模式的建立及现有计算模式的改进,对宽级配区域的泥沙输移、河床形态演化、水文水资源的管理有一定的指导意义。
[Abstract]:Sediment movement is an important scientific problem in the study of river dynamics and geomorphology. However, by the limitation of the research conditions, the previous most initial research is based on the saturated equilibrium sediment transport under the condition of uniform sand, and the influence mechanism of sediment inhomogeneity and recovery to the movement of sand and sand is still far from clear. In the study of the multiple time scales of alluvial processes, it is theoretically revealed that the bed load movement in alluvial rivers can be quickly adjusted to the state of saturated equilibrium transport, while the suspended motion requires a relatively long process, which provides a new theoretical basis for defining the applicability of the assumption of saturated equilibrium sediment transport. The study of multiple time scales is the theoretical basis, focusing on the further study of the mechanism of restoring the saturation of non-equilibrium transport processes.
The numerical simulation of saturated and unsaturated sediment transport models is compared under the framework of shallow water dynamics. The results show that the difference between the bed load motion, the saturated sediment transport model and the unsaturated sediment model is limited to the very small area near the entrance, and the saturated sediment transport model can be approximately applicable. However, the river bed is due to the river bed. There is a substantial difference between the model of suspended sediment transport, the model of saturated sediment transport and the model of unsaturated sand transport. The unsaturated model should be adopted in the numerical simulation of suspended matter. The results of the study are helpful to promote the development of mathematical model of sediment movement. And reasonable use.
The quantitative study on the variation of the saturation distance of the sediment movement of the open channel with the change of water and sediment conditions is carried out. The results show that, no matter the increase or decrease of the sediment in the upstream, the recovery saturation distance is consistent with the variation of the suspension index, that is, the suspension index is increased and the recovery saturation distance decreases, which is independent of the sediment movement model. The rules revealed generally apply to the suspended matter and the bed load movement. But the load recovery saturation distance is only a few dozen times the water depth, while the suspended matter recovery saturation distance may be as high as hundreds of times the depth of the water depth. The application of the suspended sediment transport is relatively long, and the model of unsaturated sediment transport should be adopted. At the same time, the quantitative criterion for the applicability of the concept of saturated sediment transport is provided.
The integral average model of the numerical simulation of water and sediment movement is extended to the numerical simulation of wind sand movement. On this basis, the multiple time scale theory of alluvial process is extended to the wind sand movement. The numerical example and wind tunnel experiment results show that the integral average model can accurately capture the sediment transport rate change of the wind sand movement. Compared with the complete three-dimensional model, the integral average model can greatly improve the calculation efficiency. The comparison of the multiple time scales of wind sand and water sand movement shows that the wind sand movement is similar to the water and sand movement, and the relative time scale of the load sediment concentration to the sediment carrying capacity is smaller, and the sediment concentration is not adjusted to the sand carrying capacity. It is very fast that it can reach the saturated equilibrium sediment transport very quickly, but for suspended load, the sediment concentration to the sediment carrying capacity is relatively slow.
The basic law of bedload non saturated sediment transport is extended to the non uniform sand situation, and the clean water scour test of uniform sand and non-uniform sand is carried out. The result of experimental data analysis shows that under the condition of scour, fine sand can promote the transport of coarse sand, and the coarse sand inhibits the transport of fine sand. This promotion effect is with the sand content. The inhibition effect increases with the increase of the coarse sand content, while the promotion and inhibition increases with the decrease of the flow rate. Through the analysis of the previous results of the non-uniform sand test under the equilibrium sediment transport conditions, the change trend of the inhibition and promotion is verified. The calculation of morphological change provides a new theoretical basis, which is helpful to the establishment of the new calculation model and the improvement of the existing calculation model. It has certain guiding significance for the sediment transport in the wide gradation area, the evolution of the riverbed shape, and the management of hydrology and water resources.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TV142.2

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