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尼龙网方格沙障防护效应研究
黎小娟
学位类型硕士
导师周智彬
2017-05-01
学位授予单位中国科学院大学
学位授予地点新疆乌鲁木齐
学位专业理学硕士
关键词尼龙网方格沙障 流场结构 阻沙 截留沙量 粒度 nylon mesh grid sand barrier flow field structure sand blocking sedimentation capacity intercepted sediment particle
摘要The mechanical sand barrier increases the surface roughness, absorbs and disperses thewind momentum within a certain height above the groundby changing the nature of theunderlying surface to reducethe momentum transfer between the airflow and the groundmaterial. In response to the change of the underlying surface, the effect of airflow onsurface sand, the bed on the airflow and the adjustment of wind speed profile have changed.In this paper, wind tunnel simulation and field observation experiments have been carriedout to study the flow field structure with different sizes of nylon sand barrier. Meanwhile,the morphological characteristics, sand cutoff, sand flow structure with different sizes ofnylon sand barrier and the spatial distribution characteristics of sand grain size in the sandbarrier in the hinterland of Taklimakan Desert were analyzed and explored respectively. Insummary, the reasonable pattern of nylon sand barrier was determined. The paper aim toprovide a basis for rational setting of sand barrier in desert areas and the result will providetheoretical and practical meanings respectively for further understanding the sand preventiontechniques on wind erosion protection. The main conclusions of this paper are as follows:(1)The sand barrier of nylon has a distinct districts feature. The flow field structure ofsand barrier is divided into four flow field area. Which is A(A1.A2.A3),B,C(C1.C2.C3),D.With the increase of wind speed, the deceleration zone of A1 is reduced, the contours aremore intensive and the vortex is stronger, the area of B has increased and reduced, thedegree of deceleration of C1,C2,C3,C4 has gradually reduced, the wind speed contours atD become straight gradually, respectively. The acceleration rate increased and graduallyrestored to the level before the barrier when the airflow is farther away from the sandbarrier. Apart from 14m·s-1, the greater the experimental wind speed, the more obvious thechange. With the sand barrier specifications gradually increased, the number of zones hasnot changed but the range and the vortex strength.(2)In the form of sand barrier morphology, with the increase in wind speed, Maximum sediment height has reduced. The width of the sand peak is widened. Sediment thickness isalso getting thinner. Contours are becoming more and more intensive. The smaller thespecification, the more smooth the concave surface. Which facilitates the formation ofstable concave surface. In terms of sediment transport rate, the sediment transport rate isdecreasing at the vertical height when the wind speed is small. Sediment transportincreased firstly and then reduced. When the wind speed is great. The greater the windspeed, the more trapped sand material, the greater the fluctuation of the curve, the betterthe retention effect of the nylon sand barrier. The larger the specifications, the less thetrapped sand material, the worse the protective effect.(3)The spatial differentiation characteristics of sand particle size on the surface ofnylon mesh were analyzed by field experiment. 1 m×1 m and 1.5 m×1.5 m sand grainaverage particle size along the main wind gradually increased. 1 m×2 m and 2 m×2 m sandgrain average particle size increases firstly and then decreases. Sorting factor is a goodsorting and sorting better range, the larger the specification, the better the sorting. Theoverall degree of skewness is positive and positive, the larger the specification, the greaterthe skew value. In addition to a few points, the front is a very wide peak. The averageparticle size of the four kinds of sand barrier is not correlated with the sorting coefficient,skewness and kurtosis. The kurtosis of sand grains in sand barrier is positively correlatedwith skewness and separation coefficient. The positive correlation coefficient between theskewness and the sorting coefficient is above 0.92. The vertical distribution of sedimenttransport of coarse-grained sand grains follows the decreasing law of exponential, With thedeepness of the sand barrier, the vertical distribution of sand and the amount of sedimentare affected by sand barrier. The horizontal distribution of sand grains is related to themovement mode of sand and flow field, and it has different distribution characteristics inhorizontal direction. After sand barrier, the horizontal distribution of silver sand is the mostsignificant. In the vertical direction, the degree of separation from L1-L2-L3 is slightlyworse, the skewness is very positive, the skewness coefficient is slightly larger but notsignificant. From wide to narrow, the kurtosis gradually increases. The average particle size increases with height. In the horizontal direction, from the T1-T2-T3 process, theaverage particle size of the sand increased firstly and then decreased; the best sorting at T2,the degree of skewness and kurtosis minimum. In the vertical direction, the average grainsize (Ф) at the L1 and L2 is positively correlated with the sorting coefficient, kurtosis andskewness. In the horizontal orientation, the grain size parameters of the three views (T1, T2and T3) have no significant correlation with the average particle size.
其他摘要机械沙障通过改变下垫面的性质,增加地表粗糙度,吸收和分散地表一定高度内的风动量,从而减少气流与地面物质之间的动量传递,使气流对地表沙粒的作用、床面对气流的影响以及风速廓线的调整等物理过程发生响应。本文通过风洞模拟和野外观测实验,研究了不同规格尼龙网方格沙障的流场结构,对比分析了不同规格阻沙网的形态特征、截留沙量、风沙流结构,探讨了塔克拉玛干沙漠腹地尼龙网方格沙障内沙粒粒度的空间分布特征,以确定尼龙阻沙网的合理布设模式,以期为荒漠化地区沙障的合理设置提供依据,进而为了解该地区风沙环境特征提供参考。本文主要结论如下:尼龙网方格沙障具有明显的流场分区特征,沙障前、中和后为 4 个流场作用区,分别为障前回流减速区(A:A1、A2、A3)、障顶混合加速区(B)、尼龙网带后近地表回流减速区(C:C1、C2、C3)、障后气流恢复区(D)。随着风速的增加,A1 减速区越小、A2 回流减速区等值线越密集且涡旋越强、 障顶加速区(B)面积增大,但风速增大到 14m·s-1 时减小、(C1、C2、C3、C4)减速程度逐渐减小、障后气流恢复加速区(D)的风速等值线逐渐变得平直,离沙障越远加速率越大,逐渐恢复到障前水平,除 14m·s-1 以外,实验风速越大这种变化越明显。相同风速下,规格越大沙障网格前后形成阻滞减速和涡旋减速区内的涡旋越来越弱,沙障正上方形成的混合加速区越来越小。在阻沙形态方面,随着风速的增加,最大积沙高度降低,积沙峰变宽,积沙厚度也越来越薄,等值线也越来越密集。规格越小,凹曲面越规则光滑,利于稳定凹曲面的形成,积沙厚度增加。在输沙率方面,风速较小时,输沙率在垂直高度上呈现递减规律;当风速较大时,输沙率先增加后减小。不同规格沙障截留的沙物质均呈现先减小后增加,再减小的变化规律,且随风速的增加变化越明显。风速越大,截留的沙物质越多,曲线波动也越大,尼龙网方格沙障的截留效果越好;规格越大,截留的沙物质越少,防护效果也越差。通过野外实验,分析了尼龙网方格表面沙物质粒度的空间分异特征。1 m×1 m和 1.5 m×1.5 m 的沙粒平均粒径沿主风向逐渐增大,1 m×2 m 和 2 m×2 m 的沙粒平均粒径沿主风向先增加后减小;分选系数属于分选性好和分选较好的范围,规格越大,分选性越好;偏度总体呈现正偏和极正偏,规格越大,偏度越大。除少数几个点外,锋态属于很宽的峰。四种规格沙障的平均粒径与分选系数、偏度和峰度的相关性不大。沙障内沙粒的峰度与偏度和峰度与分选系数呈正相关;偏度与分选系数呈正相关相关性系数在 0.92 以上。粗粒径沙粒(62.5~125 μm),其对应输沙量垂向分布遵循指数递减规律,且沙粒垂向分布形态和输沙量均受沙障的影响,深入沙障越深影响越大。不同粒径沙粒的水平分布受沙粒的运动方式和沙障对流场的扰动有关,在水平方向上具有不同的分布特征,经过沙障后,细沙的水平分布变化最显著。在垂直方向上,从 L1- L2- L3 的过程中分选程度略微变差,偏态均属极正偏,偏度系数略偏大但不显著,峰度逐渐增大,锋态从很宽到窄,平均粒径随着高度的增加。在水平方位,从 T1- T2- T3 的过程中,沙粒的平均粒径先增后减;在 T2 处分选性最好、偏度系数和峰度最小。在垂直方向上,L1 和L2 处沙粒平均粒径(Ф)与分选系数、峰度和偏度均呈正相关。在水平方位上,三个观点(T1、T2 和 T3)的粒度参数与平均粒径没有明显的相关关系。
学科领域生态学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14880
专题研究系统_荒漠环境研究室
作者单位中国科学院新疆生态与地理研究所
第一作者单位中国科学院新疆生态与地理研究所
推荐引用方式
GB/T 7714
黎小娟. 尼龙网方格沙障防护效应研究[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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