沙波面水沙运动特性及沙波演化规律试验研究
发布时间：2018-10-05 07:17
【摘要】：沙波运动是推移质输移的一种床面动态表现形式,它对近河底的水流结构有很大影响,也对河床的冲淤变化产生重要作用。目前,对于沙波运动规律的研究还不充分,一是由于沙波运动本身的复杂性,二是由于缺少精度高、效率高的沙波运动测量设备。因此,探索和开发高精度的新型沙波运动检测技术,并基于该技术研究沙波运动规律对于完善泥沙运动基本理论体系有重要意义。试验在室内精密水槽上进行,以非均匀塑料沙为试验沙。开发了基于图像识别的颗粒级配检测系统,并验证了其可靠性,基于该系统对水槽不同位置沙样组成进行分析;采用ADV和液态示踪剂精细采集典型沙波面处的水流紊动信息;采用高速摄像机记录不同水流强度下沙波形成、演化及沙波面颗粒运动过程;大量采集了不同水流条件下沙波形态参数。典型沙波面水流结构研究表明,沙波面水体具有明显的不稳定二次流结构,主副流强度所占比重不同对下游沙波的作用效果也不同;同一测点水体的时均流速与脉动强度具有一定的互补性;沙波对水流结构的影响范围为5cm左右水深;水流脉动最强区域为波峰点下游80cm且与波高同高处。对瞬时流速序列进行子波分析,表明了湍流具有的不同尺度、频率的涡结构特征;基于傅里叶变换将流速序列进行时间域到频率域的转换并做出能谱图,得到低频、大尺度涡结构占据水体主要能量,大、小涡间存在能量串级现象,指出了高频带小涡能量耗散率为7/4。对沙波面沙粒运动模式进行详细的阐述,联系沙波面湍流特性,建立了迎水波面沙粒不同的起动模式,对沙波面不同位置处床沙运动规律进行了机理性分析;描述了沙纹形成的非线性过程,分析了恒定和非恒定流条件下不同沙波演化时期的水流强度、波高、波速的相关关系,并细分了沙波演化周期;通过对不同水流强度下沙波形态参数的统计分析,描述了沙波形态参数与水流强度的非线性关系;引入的细度模数(Mx)参数较好的描述了水流对床沙拣选作用下的床沙组成;建立了具有统计学和动力学特点的沙波输移速度关系式和基于沙波运动的轻质沙单宽推移质输沙率公式,公式遵循量纲和谐且物理意义明确。
[Abstract]:Sand wave movement is a kind of bed surface dynamic expression of bed load transport, which has great influence on the flow structure near the river bottom, and also plays an important role in the erosion and siltation of the river bed. At present, the research on the law of sand wave motion is not enough, one is due to the complexity of the sand wave motion itself, the other is the lack of high precision and high efficiency sand wave motion measurement equipment. Therefore, it is of great significance to explore and develop a new high-precision sand wave motion detection technology, and to study the sand wave motion law based on this technology for perfecting the basic theory system of sediment motion. The test was carried out on the indoor precision tank with non-uniform plastic sand as the test sand. A particle gradation detection system based on image recognition is developed, and its reliability is verified. Based on the system, the composition of sand samples at different positions of the flume is analyzed, and the turbulent flow information at typical sand wave surface is collected by ADV and liquid tracer. High speed video camera was used to record the formation, evolution and particle movement of sand waves under different water intensity, and a large number of sand wave morphological parameters were collected under different flow conditions. The study on the flow structure of typical sand wave surface shows that the water body of sand wave surface has obvious unstable secondary current structure, and the effect of the ratio of main and secondary current intensity on the downstream sand wave is also different. The time-averaged velocity and pulsation intensity of water body at the same measuring point are complementary to each other; the influence range of sand wave on water flow structure is about 5cm depth; the strongest area of water flow fluctuation is downstream 80cm of wave peak point and the same height as wave height. The wavelet analysis of instantaneous velocity series shows that turbulence has different scales and vortex structure characteristics of frequency, and the velocity series is converted from time domain to frequency domain based on Fourier transform, and the low frequency is obtained. The large scale vortex structure occupies the main energy of the water body, and there is an energy cascade between the large and small vortices. It is pointed out that the energy dissipation rate of the small vortices in the high frequency band is 7 / 4. According to the turbulent characteristics of sand wave surface, different starting modes of sand particles in water wave surface are established, and the mechanism of sediment movement at different positions of sand wave surface is analyzed in this paper. The model of sand particle movement on sand wave surface is described in detail, according to the turbulent characteristics of sand wave surface, different starting modes of sand particles in wave surface are established. The nonlinear process of sand ripple formation is described, and the correlation among flow intensity, wave height and wave velocity in different evolution periods of sand wave under constant and unsteady flow is analyzed, and the evolution period of sand wave is subdivided. The nonlinear relationship between the sand wave shape parameters and the flow intensity is described through the statistical analysis of the sand wave shape parameters under different flow intensities, and the fineness modulus (Mx) parameter is introduced to describe the bed sediment composition under the action of water flow to bed sand selection. The relationship of sand wave transport velocity with statistical and dynamic characteristics and the formula of single wide bed load transport rate of light sand based on sand wave movement are established. The formula follows a harmonious dimensionality and clear physical meaning.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TV142
[Abstract]:Sand wave movement is a kind of bed surface dynamic expression of bed load transport, which has great influence on the flow structure near the river bottom, and also plays an important role in the erosion and siltation of the river bed. At present, the research on the law of sand wave motion is not enough, one is due to the complexity of the sand wave motion itself, the other is the lack of high precision and high efficiency sand wave motion measurement equipment. Therefore, it is of great significance to explore and develop a new high-precision sand wave motion detection technology, and to study the sand wave motion law based on this technology for perfecting the basic theory system of sediment motion. The test was carried out on the indoor precision tank with non-uniform plastic sand as the test sand. A particle gradation detection system based on image recognition is developed, and its reliability is verified. Based on the system, the composition of sand samples at different positions of the flume is analyzed, and the turbulent flow information at typical sand wave surface is collected by ADV and liquid tracer. High speed video camera was used to record the formation, evolution and particle movement of sand waves under different water intensity, and a large number of sand wave morphological parameters were collected under different flow conditions. The study on the flow structure of typical sand wave surface shows that the water body of sand wave surface has obvious unstable secondary current structure, and the effect of the ratio of main and secondary current intensity on the downstream sand wave is also different. The time-averaged velocity and pulsation intensity of water body at the same measuring point are complementary to each other; the influence range of sand wave on water flow structure is about 5cm depth; the strongest area of water flow fluctuation is downstream 80cm of wave peak point and the same height as wave height. The wavelet analysis of instantaneous velocity series shows that turbulence has different scales and vortex structure characteristics of frequency, and the velocity series is converted from time domain to frequency domain based on Fourier transform, and the low frequency is obtained. The large scale vortex structure occupies the main energy of the water body, and there is an energy cascade between the large and small vortices. It is pointed out that the energy dissipation rate of the small vortices in the high frequency band is 7 / 4. According to the turbulent characteristics of sand wave surface, different starting modes of sand particles in water wave surface are established, and the mechanism of sediment movement at different positions of sand wave surface is analyzed in this paper. The model of sand particle movement on sand wave surface is described in detail, according to the turbulent characteristics of sand wave surface, different starting modes of sand particles in wave surface are established. The nonlinear process of sand ripple formation is described, and the correlation among flow intensity, wave height and wave velocity in different evolution periods of sand wave under constant and unsteady flow is analyzed, and the evolution period of sand wave is subdivided. The nonlinear relationship between the sand wave shape parameters and the flow intensity is described through the statistical analysis of the sand wave shape parameters under different flow intensities, and the fineness modulus (Mx) parameter is introduced to describe the bed sediment composition under the action of water flow to bed sand selection. The relationship of sand wave transport velocity with statistical and dynamic characteristics and the formula of single wide bed load transport rate of light sand based on sand wave movement are established. The formula follows a harmonious dimensionality and clear physical meaning.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TV142
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