SIMULATION OF RIVER BED VARIATION BY MEANS OF FINITE ELEMENT METHOD

本文研究了均匀砂床和混合砂床在洪水期间河道收缩时的河床变化特征。从实验和数值上。试验结果表明，在泄洪输沙平衡条件下，河床有向河床靠拢的趋势。其结果是，在上升阶段河床水位降低，在下降阶段在河道收缩的上游端出现河床淤积现象。基于一维河床变化方法的数值模拟结果与实验数据吻合较好。特别是，数值方法很好地再现了实验中收缩结束时明显的堆积现象。对于混合砂床，平均直径的临界剪应力是数值结果中最重要的参数。采用水平面有限差分格式和垂直方向有限元格式的数值方法，对河湾内的三维明渠水流进行了数值计算。本文在分析河湾三维流动数值结果的基础上，提出了二维河床变分法。数值模拟结果与河湾河床变化的实验数据在一定程度上吻合。

In this study, the characteristics of river bed variation at the channel contraction during flood for uniform sand bed and mixture sand bed are investigated experimentally and numerically. From the experimental and numerically. From the experimental results it is found the tendency that the bed level approaches to the bed level on equilibrium condition of sediment discharge for flood discharge. As the results, the bed level lowers during rising stage and then phenomenon of bed aggradation during the falling stage occurs at the upstream end of the channel contraction.Numerical simulation results on the basis of one dimensional bed variation method are in good agreement with experimental data on river bed variation at the contraction. Especially, the remarkable aggradation at the end of the contraction in the experiment is well reproduced by the numerical method. And for the mixture sand bed, the critical shear stress for mean diameter is most important parameter on numerical results.The three dimensional open channel flow in the river bend is calculated by means of a numerical method of the finite differential scheme for the horizontal plane, the finite element scheme for the vertical direction. We propose the two dimensional bed variation method on the basis of the numerical results for the three dimensional flow in the river bend. The numerical simulation results are proved to coincide with the experimental data of bed variation in river bend to some extents.