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黏性细颗粒泥沙的絮凝是河流动力学中一个重要且尚未完善的研究课题。本文以分形聚集生长理论为基础,考虑了絮团破碎、泥沙浓度等因素的影响,使用三维无网格方法,在MATLAB平台上通过模拟泥沙颗粒和絮团在布朗运动、重力沉降和均匀切变水流作用下的碰撞黏结过程,研究了水流剪切作用对黏性细颗粒泥沙絮凝的影响。研究结果表明:水流作用可提高颗粒之间的碰撞几率,促进絮凝,但高水流剪切力作用下絮团破碎现象明显,因此,水流速度梯度的大小对细颗粒泥沙的絮凝有一定的影响,即絮凝速度及絮团平均粒径随水流流速梯度的增大呈先增后减的规律;均匀切变水流作用下,絮团粒径分布均匀化,絮团在垂直水流方向上发育较好且分形维数较大。本文研究成果是进一步研究天然河道中黏性细颗粒泥沙絮凝机理的成功尝试。
Flocculation of viscous fine sediment is an important and unfinished research topic in river dynamics. Based on the fractal theory of aggregate growth, the influences of flocculation, sediment concentration and other factors are considered. By using the three-dimensional meshless method, the movement of sediment particles and flocs in Brownian motion, gravity sedimentation and even The effect of shear flow on the viscous fine sediment flocculation was studied. The results show that the water flow can increase the probability of collision between particles and promote the flocculation, but the phenomenon of flocculation is obvious under the action of high flow shear force. Therefore, the magnitude of velocity gradient affects the flocculation of fine sediment , That is, the flocculation velocity and the average size of flocs increased first and then decreased with the increase of the flow velocity gradient. Under the uniform shear flow, the floc size distribution was uniform, and flocs developed well in the direction of vertical flow The fractal dimension is larger. The research results of this paper is a successful attempt to further study the flocculation mechanism of viscous fine sediment in natural rivers.