Study on Mechanism of Local Scour in downstream of Bed Protection Works

本研究针对床防护工程下游局部冲刷问题进行研究，以期建立床防护工程的合理设计。研究结论如下： 1、对哈肯河宽顶涵洞二水堰断面的局部冲刷进行了详细的实地调查，为洪水时的水流状况和冲刷深度测量做好了准备2、在床面粗糙度纵向突变情况下，从三类床面防护工程组成的粗糙床面到床面荷载动态条件下的移动床面进行了试验。讨论了床层剖面的变化和冲刷孔的最大深度，并测量了冲刷的几个阶段的流动特性。在此基础上，提出了利用富质型碎石工程减少冲刷深度的方法。 3.在此基础上，提出了采用边界拟合坐标系对河床防护工程下游局部冲刷进行二维数值模拟，并将其应用到工程中。实验。数值结果与实验结果的比较验证了该模型预测冲刷过程的能力

THIS STUDY DEALS WITH LOCAL SCOUR IN DOWNSTREAM OF BED PROTECTION WORKS IN ORDER TO ESTABLISH THE REASONABLE DESIGN OF THE BED PROTECTION WORKS. THE CONCLISIONS OF THIS STUDY CAN BE DRAWN AS FOLLOWS.1.A DETAILD FIELD SURVEY WAS CARRIED OUT REGARDING LOCAL SCOUR AT THE SECTION OF NINOARATE WEIR HAVING A BROAD CRESTE AND CULVERTS IN HYAKKEN RIVER, PREPARATIONS FOR MEASURING STREAM CONDITIONS AND SCOUR DEPTH AT A FLOOD WERE MADE.2.THE EXPERIMENTS WERE CARRIED OUT IN CASE OF SUDDEN CHANGE IN BED ROUGHNESS LONGITUDINALLY FROM A ROUGH BED CONSISTING OF THREE TYPES OF BED PROTECTION WORKS TO A MOVABLE BED UNDER DYNAMIC CONDITION OF BED LOAD. VARIATIONS OF BED PROFILE AND THE MAXIMUM DEPTH OF SCOUR HOLE WERE DISCUSSED AND FLOW CHARACTERISTICS WERE MEASURED AT SEVERAL STAGES OF SCOUR. AS THE RESULT, A METHOD TO REDUCE SCOUR DEPTH BY USING RICH-IN-NATURE TYPE RUBBLE WORKS WAS PROPOSED.3.BASED ON THESE RESULTS, 2-D NUMERICAL SIMULATIONS FOR LOCAL SCOUR IN DOWNSTREAM OF BED PROTECTION WORKS USING BOUNDARY FITTED COORDINATE SYSTEM WERE PROPOSED AND APPLIED TO THE EXPERIMENTS. COMPARING THE NUMERICAL AND EXPERIMENTAL RESULTS VERIFIED THE ABILITY OF THIS MODEL TO PREDICT THE SCOUR PROCESS