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高立式沙障风沙流场对积沙过程的动态响应
马学喜
学位类型硕士
导师李生宇
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业水土保持与荒漠化防治
关键词高立式沙障 积沙 风沙流 风场 防护效益
摘要阻沙栅栏是一种重要的机械防沙形式,具有很好的阻沙效益,它对近地表流场和沙面蚀积过程产生了很大扰动,并导致了周边的风沙地貌的不断变化,而且风沙流场特征也随地表风沙地貌的发育而动态变化。本文通过室内风洞模拟和野外实地观测,研究了高立式尼龙网沙障前后风积地貌发育过程,分析了近地表风沙流场对沙障积沙的动态响应,探讨了高立式沙障的防护效益对积沙的变化过程。主要结论如下: (1)阻沙网积沙断面形态为单峰形,积沙主要在阻沙网的下风侧。阻沙网的积沙高度和宽度逐渐增加,积沙初期和中期峰尖窄,后期峰较宽,稳定时期积沙范围主要在上风侧7H到下风侧的12H之间,积沙最高点距阻沙网下风侧的2H处。阻沙网积沙量随时间逐渐增加,上风侧积沙量占整个断面积沙量的20%,下风侧的积沙量占整个断面积沙量的80%。 (2)阻沙网极大改变局地近地表的风沙运动过程,造成风沙流饱和程度的剧烈空间变化,产生了地表蚀积交替变化。阻沙网布设初期和稳定期输沙率的变化趋势不一致,布设初始时,输沙率在阻沙网的上风侧逐渐减小,在下风侧H处输沙率最大,而稳定时期在3H处输沙率最大。 (3)随着沙障逐渐积沙,近地表风沙流场也相应发生适应性变化规律,不同时期风速廓线、平均风速加速率、风场都在变化。在布设初期,中期和中后期,平均风速和加速率逐渐减小,在5H处最小,从5H开始,又逐渐增大。而在稳定时期,平均风速和加速率H处最大,在3H处平均风速最小。从布设部位来看,在-5H处,加速率依次为:初期> 中期> 中后期> 稳定期,-2H处,加速率依次为: 中期> 中后期> 稳定期>初期,H处,加速率依次为:稳定期>中后期> 中期> 初期,3H处,加速率依次为:中期> 中后期>初期> 稳定期,5H和10H处加速率依次为: 稳定期>期中期> 中后期>初期。随着风速的增大,防风效益减小。防风效果随时间的推移而逐渐减弱,中后期防风效果增强,稳定期减弱。 (4)随着阻沙网积沙量的增多,防护效益逐渐减低。不同时期防风效益表现为:初始> 中期> 中后期> 稳定期,阻沙网在积沙的过程中,防风效益是逐渐递减的。阻沙网的出露高度与防护效益呈线性相关,随着阻沙网出露高度逐渐减小,防风效益也逐渐降低。而上风侧积沙量、下风侧积沙量和总积沙量与防护效益均呈负线性相关。随着阻沙网积沙量的增多,防护效益也逐渐减低。
其他摘要Sand blocking fence is an important form of physical sand control measures and has apparent effects on the aeolian geomorphology evolution of its periphery region while blocking drift-sand. It disturbs near-surface airflow field and the surface sand material migration process, which results in the change of dunes' morphology and the re-sorting of sand sediment. In this paper, we study the influence of high windbreak on the wind-accumulated relief evolution process, the dynamic response of near-surface airflow field to the high windbreak and the relationship between high windbreak accumulated sand and its protective efficiency by using indoor wind tunnel simulation tests and field observation. The primary conclusion is as follows: (1) The deposited sand height and width of the windbreaks were gradually increasing, and their sections were all single peak patterns, among which, the early and middle periods of peaks were narrow, but the later period of peak was a little wider; the scales of the deposited sand ranged from -7H to 12H during the stationary periods, and the top point was 2H high. The amount of deposited sand increased with increasing time, and the sand was concentrated on leeward side, the deposited sand mass ratio of windward side to leeward side was close to 1:4. (2)The windbreaks greatly changed the aeolian sandy movement progress near surface, resulting in enormous spatial changes of the aeolian sandy saturation extent and the alterations of surface erosion and sediment accumulation. The trend of the sediment discharge rate in the early stage of setting up the windbreaks was different from that in the stationary stage, the sediment discharge rate in the early stage was gradually decreasing on the windward side of the windbreaks, but it reached the maximum at the H point of the leeward side and the point of 3H during the stationary periods. (3)Adaptive changes of near-surface sand flow field were observed. Wind profile and speed-up ratio of average wind speed and change of sand flow field were different at different periods. Average wind speed and its speed-up ratio decreased gradually at initial period and the middle and later periods of experiment, but the minimum values of average wind speed and its speed-up ratio were found at 5H, and they increased gradually after the point of 5H point. However, at stable period, the maximum values of average wind speed and its speed-up ratio were found at H point and the minimum values of average wind speed was found at 3H point. According to the points of the experiment, the sequence of speed-up ratio was initial period, middle period, the mid-late period and stable period at the point of -5H; At the point of -2H, the sequence of speed-up ratio was middle period, the mid-late period, stable period and initial period; At the point of H, the sequence of speed-up ratio was stable period, the mid-late period, middle period and initial period; At the point of 3H, the sequence of peed-up ratio was middle period, the mid-late period, initial period and stable period; At the points of 5H and 10H, the sequence of speed-up ratio was stable period, middle period, the mid-late period and initial period. Windproof efficiency decreased gradually with the increase of wind speed and time and it increased at the middle and later periods but at stable period weakened. (4)The windproof efficiency decreased gradually with the increasing accumulation of sand in the sand-blocking mesh. Windproof efficiency at different stages was initial period>middle period>the mid-late period>stable period. The windproof efficiency decreased gradually in the process of accumulating sand in the sand-blocking mesh. There was a linear correlation between the exposed height of sand-blocking mesh and windproof efficiency, that is, windproof efficiency decreased gradually with the decreasing exposed height of sand-blocking mesh. However, a negative linear correlation between the windward accumulating sand quantity, the leeward accumulating sand quantity, the total accumulating sand quantity and windproof efficiency was found.
学科领域水土保持与荒漠化防治
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14661
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
马学喜. 高立式沙障风沙流场对积沙过程的动态响应[D]. 北京. 中国科学院大学,2015.
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