基于水沙相干的床面颗粒随机状态特征及对推移质输移的影响

The motion of sediment on the bed is a physical process in river with frequent fluid-solid coherence and randomness. Fine considerations of the sediment particle state, interactions between particles and near-bed flow turbulence are the bases for in-depth study of the movement law of the sediment on the bed. Based on PIV/PTV technology and turbulent stochastic theory, this project takes the micro-level random state of the particles on the bed as the starting point, and takes the research on the random behavior characteristics of particles under the influence of flow-sand coherence in near-bed area as the main line. By means of systematic theoretical analysis and series of tests, the boundary effect of the microstructure on the bed will be figured out; Based on the particle wagging constraint model and the reasonable definition of the critical threshold of particle dynamic and static state, the pulsation effect of near-bottom turbulence on the particles in waiting states of different levels under the constraint of microstructure will be studied. The incipient mode of the particles and the relevant resonant excitation frequency will be explored; By investigating the random distribution of the state parameters of particles and the near-bed turbulence power spectrum characteristics, it will be revealed that the response mechanism of the particle state parameters (particle waiting time and particle activity, etc.) to the near-bed flow turbulent; Multi-scale correlation analysis is used to study the effects of near-bed flow-sand coherence and sand-sand coherence on the temporal and spatial variation characteristics of bedload transport. This study has certain scientific significance for understanding the relationship between the state characteristics of the particles on the bed and the collective behavior of bed load, predicting the transport and the diffusion of bed load. The output is beneficial to promote the development of river and sediment scientific theory system.

床面泥沙运动是河流中流固相干频繁、随机性很强的物理过程。精细考虑床面颗粒状态、粒间作用与近底水流紊动影响，是深入研究床面推移质泥沙运动规律的基础。本项目借助PIV/PTV技术与紊流随机理论，以微观颗粒随机状态研究为出发点，以近底水沙相干影响下的颗粒随机行为特征研究为主线，通过系统理论分析和系列试验研究，厘清床面微组织结构的边界效应；基于颗粒抖动约束模型，合理界定颗粒动、静态的临界阈值，研究在微组织结构约束下，颗粒不同层级等待中近底紊流的脉动效应，探寻颗粒起动模式与谐振激发频率；通过研究床面颗粒状态参量（等待时间及活跃度等）的随机分布规律与近底紊流功率谱特征，揭示颗粒状态转化对水流的响应机制；最后采用多尺度关联分析，阐明近底水沙相干、沙沙相干对推移质输移时空变化特性的影响。本研究为认识颗粒状态特征与集群随机运动的关联、精准预测推移质输移与扩散提供科学依据，促进河流泥沙科学理论体系的发展。

床面泥沙运动是河流中流固相干频繁、随机性很强的物理过程。限于研究手段、观测仪器的限制，目前还不能准确的了解床面颗粒状态、粒间作用机制，以及近底水流紊动对颗粒运动的影响。因此研发试验观测技术，深入研究床面单颗粒状态特征及其与推移质输移规律的关联，是推动泥沙运动力学理论发展的需求，也是河道整治工程基础安全评价技术应用的需求。本项目借助PIV/PTV技术与紊流随机理论，以微观颗粒随机状态研究为出发点，以近底水沙相干影响下的颗粒随机行为特征研究为主线，开展了基本理论分析、试验观测技术研发和系列试验研究。研发了水下无干扰的床面颗粒图像采集技术与追踪识别程序PTP，采样效率提高1倍以上；提出了床面微组织结构典型类型与床面边界效应，引入活性粒子及分级等待的识别模式，提出了累积净位移0.25D50的颗粒临界运动阈值；研究了在微组织结构影响下，颗粒在不同层级等待中起动特点与起动概率；探寻了床面颗粒状态参量（速度、加速度、活跃度等）的随机分布规律，给出了它们的PDF分布函数以及函数的尾部收敛特性；采用象限分析法研究了近底水流紊动特征，通过脉动强度的频谱分析，探寻了近底水流紊动与床面不同颗粒状态的相应关系，提出了水流脉动强度对颗粒运动速度影响很敏感的范围，提出了1.5倍、2.5倍脉动强度两个特征值，揭示了颗粒状态转化对水流的响应机制；采用多尺度关联分析，阐明了近底粗细沙之间相互作用对床面泥沙运动的影响，揭示了由驼峰曲线显示的非均匀沙相干作用对推移质输移率的制约机制。研究成果对促进河流动力学基础理论发展、提高推移质泥沙试验研究水平，具有一定科学意义与应用价值。