Study on Sediment Transport Process on Permeable Bed

为了预测具有透水边界和渗流的天然河流中的冲积现象，有必要建立一个描述透水河床上非平衡输沙过程的模型，该模型的组成要素是取沙速率和步长。在本研究中，拟提出一个合理的公式来估算具有稳定蒸腾速度的透水床上砂粒的吸附速率，并对推导出的公式进行实验验证。对于步长，首先进行了实验研究，并根据其信息，提出了一种合理的步长估计方法。从理论上分析了蒸腾速度对沙粒初始运动和输运的影响。同时，利用视频胶片分析系统，在实验室水槽中进行了设计实验，获得了精度较高的实验数据。本文的研究结果将为河流中各种河流过程的分析提供更多的参考。其次，为了使上述模型更加准确，对流动结构进行了检验。在高渗透性多孔介质中，当渗流伴随着其上的流动时，表面流动与渗流之间的相互作用不可忽视。在高渗透率情况下，由于非线性项占主导地位，渗流的达西定律不一定适用。这种非线性使得自由表面流向多孔介质内部固有的压力波动的传播以及随后的渗流速度波动具有各向异性，随后出现的表观雷诺应力起到了明显的动量交换作用。即渗流受较快的自由表面流的阻力影响。在本研究的这一部分。建立了该机制的物理模型来评价诱导渗流速度，并考察了其对泥沙输运过程的影响。通过水槽试验验证了理论结果。少

In order to predict the alluvial phenomenon in the natural rivers with the permeable boundaries and seepage flow, it is necessary to establish a model to describe non-equilibrium sediment transport process on a permeable bed, of which constituent elements are sediment pick-up rate and step length. In this study, it is intended to propose a reasonable formula to estimate the pick-up rate of sand particles on a permeable bed with steady transpiration velocity and to verify the derived formula experimentally. As for the step length, firstly the experimental research is intended, and based on its information, a reasonable way of estimating the step length is proposed.Incipient motion and transport of a sand particle affected by transpiration velocity has been theoretically analyzed. Meanwhile, a devised experiment has been carried out in laboratory flume to obtain the experimental data in good accuracy, by making use of a video film analyzing system. The obtained results of this study will … More be available for analyses of various kinds of fluvial process in rivers.Next, in order to make the above mentioned model exact the flow structure has been examined. When the seepage flow in the highly permeable porous medium is accompanied with the flow over it, the interaction between surface flow and seepage flow cannot be neglected. In case of high permeability, Darcy law for seepage flow is not necessarily applicable because of the predominance of non-linearity term. This non-linearity makes the propagation of the pressure fluctuation inherent to the free surface flow into the inside of the porous medium and the subsequent fluctuation of seepage flow velocity anisotropic, and the subsequent appearance of apparent Reynolds stress plays a role of appreciable momentum exchange. Namely seepage flow is affected by the drag of the faster free usrface flow. In this part of this study. a physical modelling of this mechanism is formulated to evaluate the induced seepage velocity, and the effect on the sediment transport process is examined. The theoretical results are verified by flume experiments. Less