【摘要】：沙波運動是推移質(zhì)輸移的一種床面動態(tài)表現(xiàn)形式,它對近河底的水流結(jié)構有很大影響,也對河床的沖淤變化產(chǎn)生重要作用。目前,對于沙波運動規(guī)律的研究還不充分,一是由于沙波運動本身的復雜性,二是由于缺少精度高、效率高的沙波運動測量設備。因此,探索和開發(fā)高精度的新型沙波運動檢測技術,并基于該技術研究沙波運動規(guī)律對于完善泥沙運動基本理論體系有重要意義。試驗在室內(nèi)精密水槽上進行,以非均勻塑料沙為試驗沙。開發(fā)了基于圖像識別的顆粒級配檢測系統(tǒng),并驗證了其可靠性,基于該系統(tǒng)對水槽不同位置沙樣組成進行分析;采用ADV和液態(tài)示蹤劑精細采集典型沙波面處的水流紊動信息;采用高速攝像機記錄不同水流強度下沙波形成、演化及沙波面顆粒運動過程;大量采集了不同水流條件下沙波形態(tài)參數(shù)。典型沙波面水流結(jié)構研究表明,沙波面水體具有明顯的不穩(wěn)定二次流結(jié)構,主副流強度所占比重不同對下游沙波的作用效果也不同;同一測點水體的時均流速與脈動強度具有一定的互補性;沙波對水流結(jié)構的影響范圍為5cm左右水深;水流脈動最強區(qū)域為波峰點下游80cm且與波高同高處。對瞬時流速序列進行子波分析,表明了湍流具有的不同尺度、頻率的渦結(jié)構特征;基于傅里葉變換將流速序列進行時間域到頻率域的轉(zhuǎn)換并做出能譜圖,得到低頻、大尺度渦結(jié)構占據(jù)水體主要能量,大、小渦間存在能量串級現(xiàn)象,指出了高頻帶小渦能量耗散率為7/4。對沙波面沙粒運動模式進行詳細的闡述,聯(lián)系沙波面湍流特性,建立了迎水波面沙粒不同的起動模式,對沙波面不同位置處床沙運動規(guī)律進行了機理性分析;描述了沙紋形成的非線性過程,分析了恒定和非恒定流條件下不同沙波演化時期的水流強度、波高、波速的相關關系,并細分了沙波演化周期;通過對不同水流強度下沙波形態(tài)參數(shù)的統(tǒng)計分析,描述了沙波形態(tài)參數(shù)與水流強度的非線性關系;引入的細度模數(shù)(Mx)參數(shù)較好的描述了水流對床沙揀選作用下的床沙組成;建立了具有統(tǒng)計學和動力學特點的沙波輸移速度關系式和基于沙波運動的輕質(zhì)沙單寬推移質(zhì)輸沙率公式,公式遵循量綱和諧且物理意義明確。
[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.
【學位授予單位】：華北水利水電大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TV142

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