【作者】 周家俞；

【导师】 陈立；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2005， 硕士

【摘要】 挟沙水流的运动规律是泥沙运动力学中基本问题之一。在挟沙水流中,泥沙颗粒在水流的作用下起动、悬浮、输移,同时又对水流产生影响。水流与泥沙颗粒之间是相互制约、相互影响的。在自然界河流中,泥沙主要以悬移质的形式输移,而悬移质泥沙悬浮输移与颗粒大小有着密切的联系。从力学角度上讲,悬移质泥沙受水流紊动扩散而悬浮,受重力作用而沉降,所以颗粒的悬浮输移主要取决于水流的紊动特性。水流能够悬浮起的泥沙颗粒大小与水流紊动作用有着直接联系,水流紊动强度强弱决定泥沙颗粒大小,而泥沙颗粒大小也反作用于水流强度。因此,研究泥沙颗粒运动对深入认识挟沙水流运动输移的内在机理,推动泥沙理论的不断发展具有重要的意义。 本文采用理论分析结合室内试验的方法,对泥沙影响挟沙水流流速分布的规律、悬移质泥沙颗粒的悬浮特性及其影响因素作了较系统的研究。试验中,采用美国Sontek公司生产的声学多普勒流速仪MicroADV测量计算瞬时流速、紊动强度等。 由于泥沙颗粒与水流结构之间的相互影响以及不同水流条件下这种相互影响的复杂变化,清水和挟沙水流的流速分布不同。在分析现有流速分布公式结构的基础上,指出目前指数流速分布公式中的不足,并依据水槽试验资料对挟沙水流指数型流速分布公式进行了分析。同时对指数流速分布公式中的指数和系数随泥沙粒径、泥沙浓度的变化进行了分析,结果表明:在相同或相近的水流强度下,指数流速分布公式中系数随泥沙浓度的增加而增大;在水流强度、泥沙浓度相当的情况下,指数随粒径的增大而减小;相同或相近的水流强度下,指数随泥沙浓度的增加而增大。 泥沙粒径与泥沙浓度沿垂线分布均呈现出上小下大、上稀下浓的规律。采用泥沙中值粒径代表泥沙级配的粗细,通过试验分析了泥沙粒径、浓度、水流强度等因素对悬移质泥沙粒径沿垂线的分布的影响规律进行了研究。结果发现:在一定的水流条件下,泥沙颗粒较粗时,泥沙中值粒径沿垂线(自床面向上至水面)呈递减规律;泥沙颗粒较细时,递减规律不明显。在水流强度和泥沙颗粒粗细相同的条件下,泥沙浓度越大,相同水深位置的泥沙颗粒组成相对较粗;而在相同的泥沙浓度和泥沙颗粒粗细情况下,水流条件越强,相同水深位置的泥沙颗粒中值粒径越大,紊动强度也是如此。 对泥沙中值粒径和水流紊动强度沿垂线分布之间的内在联系进行了探索,发现两者沿垂线分布有一定的相似性,即从总体上来说,无论是泥沙颗粒中值粒径还是更多还原

【Abstract】 Movement law of flow is one of the most basic problem in mechanics of sediment transport. Sediment particle begin to move at the action of the flow.but it effect the flow itself during the course of moving, in nature river, sediments is it move in the form of suspended sediments mainly, it have close contacts with size of particle to move to suspend, Speaking from the mechanics angle , suspended sediments move and suspend due to flow turbulence, subsided by the action of gravity. So particle suspend depend on the characteristic of turbulence mainly. Sediment particle size be suspended have direct connections with turbulence function, the flow turbulence intensity determine sediment particle size , and sediment particle size act on the turbulence intensity, too. It is significance to researching sediment particles’ move for deeply knowledging the inner mechanics of sediment transport and suspend and promoting the development of sediment theory.In the paper , theory analyzed and experimentation research are adopted. Systemly researched the sediment influences distributed law of the velocity of flow,suspended characteristic of suspended sediment partilces and effction ingredients ,During the course of experimence, a three-dimensional MicroADV(Acoustic Doppler Velocimeter) is carried on in this paper, and measure the distribution of time-mean velocity in sediment-laden flow, offering the thereunder for exact calculating flow turbulence intensity.Because influencing each other between the sediment particle and flow structure and this kind of complicated change influencing each other under different hydraulic condition, the velocity of flow is distributed differently in clear water and in sediment-laden flow.At the beginning, we researched the formula structure of the distribution of velocity of flow according to the experimental data in sediment-laden flow, pointed out that the drawbacks in the existing formula of exponential of velocity distribution and verifying the formula,the general form of exponential of velocity distribution has been established, and test the formula by the experimental data, the result was very well. What’s more, researched the index and coefficient of the exponential of velocity distribution, found the closed relation between the two parameters with intensity of flow and sediment concentration. It was analyzed that the influence of interaction between sediment particles and flow to the distribution of velocity of flow with different sediment condition and flow intensity. Based on verifying the existing distribution formula application by the experimental data, a new formula of exponential of velocity distribution was proposed, at the same time, the variational law of coefficient and index in the new formula with sediment concentration, diameter of particles and hydraulic condition is analyzed, It has been concluded that coefficient increases with increasing sediment concentration,hydraulic condition and diameter of particles; However index decreases with increasing diameter of particles, and increases with increasing sediment concentration.The difference of the formula of the distribution of velocity in clear flow and in sediment-laden flow is mainly because the flow inner structure effected by the variation of sediment and hydraulic condition.Exerimental results indicate that there is a law of sediment particles size, i.e., sediment particle size along depth (whether bed face upward to surface of water since) decreasing law when the sediment particle size is relatively larger. Thinner particle does not have the law or the phenomenon, because they wash qualities of rushing down, it is suspended and transfered swimming all the time. It have studied the distribution law along depth of sediment particles under sediment concentration, sediment particles size and hydraulic condition, shown that: sediment particles sorting not only closely related to sediment concentration, hydraulic condition and sediment particles one’s own relevant, Particle sorting varies with the above three kinds of conditions: the sediment particles size increase with increasing sediment concentration, with increasing hydraulic condition, with increasing sediment particle oneself. So is flow turbulence?, The big or small and even degree of sediment and particle is an important factor of influence particle sorting ?Sediment particles is Suspended in the sediment-laden flow because of the flow turbulence, and setting due to gravity action. Inherent motive force that the sediment particle suspended —the flow turbulence? Above the discussion, one have studied inherent relation between sediment particles size and the flow turbulence intensity along depth ? Show that sediment particle size and the flow turbulence intensity along to consistency better in y/h>0.1 along depth0 Namely general speaking, no matter sediment particle size or the flow turbulence intensity along depth, which increase with increasing distance from the position to bedc Fanaly,according to test materials , establish relation between middle size of sediment particles and flow turbulence intensity at the one position along depth.更多还原