沙波床面推移质颗粒运动及其与沙波输移相互作用机理研究

Sand waves, or bedforms, are ubiquitous in the bottom of the alluvial river. However, the mechanism of initiation, formation and development of bedforms are still an open question. Most of the existing research about the bedforms are focus on the development of bedforms itself, whereas pay less attention to the movement of the particles, which formed the bedforms. On the other hand, research on aspects of the movement of bedload particles are mainly based on flat bed, which with great differences with the actual conditions of the natural alluvial river...Aiming at above problems, in this research proposal, a series flume experiment will be carried out to explore the internal mechanisms between the bedforms and the water flow, also the bedload particles movement over the bedforms. The experiments would conduct on a large flume of 50m long, 1.0m wide and 1.2m high. The particles movement trajectory under different boundary conditions would be obtained by using the high speed camera and digital image processing technology. The basic characters of the particle movement, such as the move or stop time of duration, velocity, and distance of the saltation will be thoroughly studied. On the other hand, The development process of the ridge and crest of subaqueous bedforms would obtained by the digital image processing and ultrasonic measurement system. By comparing measurement of the bedload flux with different methods, relationship between bedload particles movement, its effect on bedform migration, near bed flow coherent structure, and comprehensive flow resistance would be quantitative identified. Through this research, a comprehensive bedload transport model based on the near wall flow structure, stochastic process movement of the particles and bedform migration would be tentatively proposed.

沙波普遍存在于冲积河流底部，而目前对沙波形成、发展机理方面的认识仍有待深入。已有关于沙波方面的研究往往只关注床面形态本身的发展，对于组成床面形态的颗粒如何运动关注不够；另一方面关于推移质颗粒运动规律方面的研究则均集中于平整床面，与实际冲积河流天然条件存在较大的区别。基于以上问题，本项目拟在50.0m长1.0m宽1.2m高的大型水槽中开展沙波床面推移质颗粒运动特性及其对沙波整体输移影响方面的试验研究，利用高速摄影数字图像处理技术获取沙波床面条件下的泥沙颗粒运动轨迹，深入研究沙波不同部位泥沙颗粒的随机走、停时间，运动速度，跃移距离等基本规律；采用数字图像处理与超声波地形仪相结合的方法，对沙波波缘发展、宏观输移过程进行同步测量，并与上述颗粒运动特性、局部紊流相干结构测量分析结果相结合，定量分析沙波顶部颗粒层输移与沙波整体输移之间的关系，初步构建基于沙波床面微观颗粒随机运动的推移质输移模型。

沙波床面形态普遍存在于冲积河流底部，对泥沙运动和河床演变具有重要影响，受量测技术所限，目前关于沙波及床面形态的形成、发展机理方面的认识还远远不足。本项目在长50m宽1m高1.2m的大型玻璃水槽中开展了沙波床面推移质系列试验研究，采用三维激光扫描仪测量了不同水流条件下的沙波床面形态，以高速摄像机获取了沙波床面颗粒运动信息，分析了不同条件下床面形态形成和发展过程，识别了随水流强度由低至高形成依次出现的低起伏三维形态、准二维沙垄、二维沙垄、三维沙垄、流向沙脊、床面交替冲淤藕节状、连片鱼鳞状、舌状沙波等不同的床面形态发展阶段。分析了沙波床面条件下的河床阻力及推移质输沙率情况，指出高强度推移质运动所带来的动床附加阻力是除传统沙粒阻力、形状阻力之外的重要阻力单元，同时沙波床面形态存在可能是造成推移质输沙率估算偏差较大的重要原因。动床床面形态对流速分布影响较大，床面形态存在条件下的动床水流流速分布有别于已有定床人工沙波测量结果。受水流紊动影响，推移质泥沙颗粒运动同样存在着较强的随机运动特性，除此之外，不同床面形态部位泥沙颗粒运动强度同时存在确定性差异，其中高强度颗粒运动区域位于沙波迎水面尾部，而在沙波背水面及下游沙波迎水面首部区域泥沙颗粒运动强度较小。