【作者】 乔春林；

【导师】 牟献友；

【作者基本信息】 内蒙古农业大学 ， 水利水电工程， 2017， 硕士

【摘要】 由于传统桥墩冲刷防护技术的局限性,本文在前人的研究成果基础上,引入环翼型防冲板和开缝组合的新型防护措施,通过主动减小墩前下降水流和墩侧绕流对河床进行防护。为探究组合防护的防冲刷效果,在三组流量-水位条件下,采用半幅形状、不同安装位置的环翼型防冲板,与不同缝高、不同缝位置的墩缝进行系统的组合,进行室内物理模型试验。首先以冲坑特征、桥墩周围时均流速为研究指标,定量分析开缝防护及开缝和防冲板组合防护的防冲刷效果,进而再以桥墩周围时均流速、紊动强度和紊动动能为研究指标,进一步分析组合防护各方案的防冲刷效果,进而得出最优的组合方案。试验结论主要包括:(1)在相同缝高和缝位置的条件下,组合防护的冲坑深度减小率明显大于开缝防护的,开缝靠近河床的冲坑深度减小效果是优于开缝靠近水面的,冲坑深度减小效果最佳是在组合防护中开缝靠近河床的工况下;两类防护下,随着缝高增加,冲坑深度明显减小。(2)相对于桥墩无防护而言,两类防护都可减小墩前的垂向时均流速,进而减弱下降水流对河床的冲击,并且组合防护对下降水流的减弱效果明显优于开缝防护。(3)组合防护中开缝靠近河床时,防冲板和缝的组合,使得二者对防冲板以下位置的垂向时均流速的减小作用明显增强,其优于开缝靠近水面时和防冲板的组合效果,开缝靠近河床和防冲板距离河床的高度为1/3水深的组合对墩前的垂向时均流速的减小效果在六种组合防护的方案中最优。(4)组合防护中开缝靠近河床时,防冲板和缝的组合,可明显降低近河床的垂向紊动强度值及紊动动能值,使得水流与河床的相互作用减弱,从而减小水流对桥墩底部周围的冲刷作用,由垂向紊动强度和紊动动能的分析可知,开缝靠近河床和防冲板距离河床的高度为1/3水深的组合在六种组合防护的方案中最优。研究表明,对于圆柱形桥墩的局部冲刷,环翼型防冲板和开缝组合防护效果突出,为深入研究桥墩防冲刷的组合防护奠定了 一定的基础。更多还原

【Abstract】 Owing to the limitations of traditional protection technology for piers local scour,based on the previous research results,the new protection measure was introduced,which combined ring-wing plate with slot.It protected riverbed by reducing falling water and flowing around the piers side.To study the influence of preventing scour,under the condition of three kinds of discharge-water level,by combining the half round shape,different installation position of plate with the different height,different location of slot,the physical model test was carried out.First of all,the influence of slot prevention and the combination prevention were analyzed quantitatively by using the characteristics of the scour hole,the average velocity around the piers.Proceeding to the next step,in order to get the optimal combination scheme,the combination prevention were analyzed quantitatively by using the average velocity,turbulence intensity and turbulence kinetic energy around the piers.The conclusions included:(1)Under the condition of the same height and position,the decrease rate of the pit depth was significantly greater than that of the slotted protection,the effect of reducing the pit depth under the slot position close to the riverbed was better than that of the slot position near the water surface,the best way to reduce the depth of the pit was that the slot position close the riverbed under the combined protection.Under the two kinds of protection,with the increase of the slot’s height,the depth of the scour pit decreased obviously.(2)Relative to the piers without protection,two kinds of protection can reduce the vertical average velocity before piers,thus,weakening the impact of the downward flow to river bed,and the combination protection weakened the effect of falling water was significantly better than the slotted protection.(3)Under the combination protection,when the slot was close to the river bed,the combination of the plate and slot made the reducing function of vertical average velocity under plate position obviously enhance,the effect was better than that of the combination of slotted near the water surface with plate.In the six combinations,the effect of the combination of slot which closed to the river bed and the plate which located on the third of water depth on the decrease of the vertical average velocity in front of the piers was the best.(4)Under the combination protection,when the slot was close to the river bed,the combination of the plate and slot could obviously reduce vertical turbulence intensity and turbulence kinetic energy on the near river bed,so that the interaction between the water flow and the river bed was weakened,and the scouring action of the water flow to the bottom of the pier was reduced.Based on the analysis of the vertical turbulence intensity and turbulent kinetic energy,the combination of slot which closed to the river bed and the plate which located on the third of water depth was the best in the six combinations.The study indicates that the effect of the combination prevention is prominent for local scour of cylinder piers.It provides a basis for combination prevention to piers scour.更多还原