风成沙波纹数学模型综述     

李猛  董治宝  张正偲 《中国沙漠》2013,33(5):1285-1292

风成沙波纹是风力作用下地表形成的最基本的地貌类型。近年来,随着计算机技术的迅猛发展,风成沙波纹数值模拟研究越来越引起重视。本文简要介绍了风成沙波纹数学建模的理论基础,并将已有的风成沙波纹数学模型划分为3类,着重介绍了几个经典的风成沙波纹数学模型,详细列举了这些模型的假设条件和数学表达,分析了他们的优缺点。目前,风成沙波纹数学建模的两个基本理论依据为:一个是地表坡度变化导致的蠕移沙通量的变化;另一个是跃移长度随沙床面高度变化的规律,但目前关于此理论的研究并不多。最后,总结和展望了这一领域的研究方向和前景。  相似文献   

基于高速摄影技术的风沙流输沙通量剖面的风洞实验测量     

蒋缠文  董治宝  王晓艳 《中国沙漠》2016,36(5):1230-1237

风沙研究者非常重视对输沙通量随高度变化特征的研究,并为寻找可靠的测量手段付出了不懈的努力。基于高速摄影技术获得的沙粒平均水平速度与沙粒数的垂直剖面,推导了较低风速下环境风洞内输沙通量的垂直剖面。结果表明：沙粒平均水平速度随高度呈幂函数增加,颗粒浓度随高度的算数平方根呈指数衰减。由颗粒平均水平速度剖面与浓度剖面的乘积可获得输沙通量剖面。所获得的输沙通量随高度变化曲线在距床面1~3 mm处均有一个明显的拐点,拐点上方输沙通量随高度呈指数衰减。在床面与拐点之间输沙通量没有明显的变化趋势,这可能是由于气流中颗粒间的碰撞以及颗粒与床面碰撞的影响。平均跃移高度和相对衰减系数是描述输沙通量随高度变化的两个重要参数,两者有着很好的相关性,表明了随着风速增加和沙粒粒径减小跃移颗粒可以达到更大的高度,随着风速减小与粒径增大,输沙通量迅速衰减。  相似文献   

风沙二相流运动特点的分析   总被引：13，自引：0，他引：13  

刘大有  贺大良 《地理学报》1996,51(5):434-444

本文以平坦沙漠上定常，充分发展的风沙二相流为例分析了颗粒的跃移运动，在这种运动中颗粒吸收气流的机械能和水平动量向下输送，并在落地时传递给床面。本文还用拟流体观点分析了固相运动的特点：在床面上有较大的滑移速度，有较大的垂向速度脉动，例题垂向的平均速度却为零，等等。  相似文献   

Crust strength: a wind tunnel study of the effect of impact by saltating particles on cohesive soil surfaces   总被引：1，自引：0，他引：1  

M. A. Rice  I. K. McEwan 《地球表面变化过程与地形》2001,26(7):721-733

A wind tunnel study examined the effect of distributions of saltating particles on sediment surfaces which were characterized by distributions of their tensile strength. The sediments consisted of varying proportions of large sand‐sized particles with a fine particle cement. The energies of the impacting particles and the surface strengths were compared with the mass of material lost from the surface. It is important to consider distributions of parameters rather than mean values only, since abrasion and erosion may occur from surfaces not predicted from average strength and saltation velocities. At the impact velocities used in this study (mean velocity 4·4 m s^?1, with standard deviation of 0·51), surfaces containing less than 12 per cent fine material were easily eroded, but insignificant erosion occurred when the fine particle content exceeded 60 per cent. Small amounts of cementing material were easily ruptured, allowing the large sand grains to be moved (largely in creep) by the bombarding particles. A significant amount of energy was lost to the bed. As the percentage of fine material increased, the surface became more difficult to break up and less energy was lost to the bed. The probability that erosion will occur for known energy distributions of impacting particles and surface strength can be calculated and the mass loss increases exponentially with a decrease in the percentage of fine cementing particles. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

A simple low‐cost sand catcher for wind‐tunnel simulations     

Wim M. Cornelis  Donald Gabriels 《地球表面变化过程与地形》2003,28(9):1033-1041

A simple low‐cost sand catcher has been developed for use in wind‐tunnel experiments. It is 500 mm high with a 300 mm by 20 mm inlet opening, and is designed to measure total mass transport directly. The length is 280 mm and its walls slowly expand at an angle of 5·6°. The top view is similar to that of the widely used BSNE sampler. Each sidewall is vented with three ventilation screens. Two sets of experiments were conducted on dune sand and at different wind velocities to investigate to what degree the catcher samples isokinetically, ef?ciently and non‐selectively. The results indicate that the catcher measures suf?ciently isokinetically (inlet wind velocity over outside wind velocity >0·9). Catch ef?ciency was around 0·75 and the degree of non‐selectivity was >0·80 for 95 per cent of the particle sizes of the test material. It was also observed that the in?uence of wind velocity on the tested sampler characteristics was of minor importance so that no speci?c corrections need to be made for different wind velocities. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Impact–entrainment relationship in a saltating cloud     

Zhibao Dong  Xiaoping Liu  Fang Li  Hongtao Wang  Aiguo Zhao 《地球表面变化过程与地形》2002,27(6):641-658

The problem of impact–entrainment relationship is one of the central issues in understanding saltation, a primary aeolian transport mode. By using particle dynamic analyser measurement technology the movement of saltating particles at the very near‐surface level (1 mm above the bed) was detected. The impacting and entrained particles in the same impact–entrainment process were identified and the speeds, angle with respect to the horizontal, and energy of the impacting and entrained sand cloud were analysed. It was revealed that both the speed and angle of impacting and entrained particles vary widely. The probability distribution of the speed of impacting and entrained particles in the saltating cloud is best described by a Weibull distribution function. The mean impact speed is generally greater than the mean lift‐off speed except for the 0·1–0·2 mm sand whose entrainment is significantly influenced by air drag. Both the impact and lift‐off angles range from 0° to 180°. The mean lift‐off angles range from 39° to 94° while the mean impact angles range from 40° to 78°, much greater than those previously reported. The greater mean lift‐off and especially the mean impact angles are attributed to mid‐air collisions at the very low height, which are difficult to detect by conventional high‐speed photography and are generally ignored in the existing theoretical simulation models. The proportion of backward‐impacting particles also evidences the mid‐air collisions. The impact energy is generally greater than the entrainment energy except for the 0·1–0·2 mm sand. There exists a reasonably good correlation of the mean speed, angle and energy between the impacting and entrained cloud in the impact–entrainment process. The results presented in this paper deserve to be considered in modelling saltation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

A method for establishing the critical threshold for aeolian transport in the field   总被引：1，自引：0，他引：1  

John E. Stout 《地球表面变化过程与地形》2004,29(10):1195-1207

A basic feature of any wind‐eroding surface is its threshold – the wind speed at which sediment transport is initiated. A new method was developed and tested that allows for the rapid determination of threshold under natural wind conditions in the ?eld. A mathematical expression that relates saltation activity and relative wind strength was reformulated so that threshold may be calculated from measurements of saltation activity and the mean and standard deviation of wind speed. To test the new method and determine its usefulness, a ?eld experiment was performed within a region of low‐relief dunes on the Southern High Plains of West Texas. The experimental system consisted of a 2‐m meteorological tower and a piezoelectric saltation sensor. It was found that during periods of active aeolian activity, threshold values could be calculated every 5 minutes. This new method allows for routine monitoring of surface threshold conditions in the ?eld. Example threshold calculations are presented and they demonstrate that the method works well. Published in 2004 by John Wiley & Sons, Ltd.  相似文献   

Validation of WEPS for soil and PM10 loss from agricultural fields within the Columbia Plateau of the United States     

G. Feng  B. Sharratt 《地球表面变化过程与地形》2007,32(5):743-753

Wind erosion from agricultural fields contributes to poor air quality within the Columbia Plateau of the United States. Erosion from fields managed in a conventional winter wheat–summer fallow rotation was monitored during the fallow period near Washtucna, WA, in 2003 and 2004. Loss of soil and PM10 (particulates ≤10 µm in diameter) was measured during six high wind events (sustained wind speed at 3 m height >6·4 m s^?1). Soil loss associated with suspension, saltation and creep as well as PM10 emission was used to validate the Wind Erosion Prediction System (WEPS) erosion submodel. Input parameters for WEPS simulations were measured before each high wind event. The erosion submodel produced no erosion for half of the observed events and over‐predicted total soil loss by 200–700 kg ha^?1 for the remaining events. The model appears to over‐predict total soil loss as a result of overestimating creep, saltation and suspension. The model both over‐predicted and under‐predicted PM10 loss. High values for the index of agreement (d > 0·5) suggest that the performance of the model is acceptable for the conditions of this study. While the performance of the model is acceptable, improvements can be made in modeling efficiency by better specifying the static threshold friction velocity or coefficients that govern emissions, abrasion and breakage of silt loams on the Columbia Plateau. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Testing the auto‐abrasion hypothesis for dust production using diatomite dune sediments from the Bodélé Depression in Chad     

《Sedimentology》2018,65(4):1322-1330

This study examines the role of quartz sand in the production of dust using mixtures of quartz sand from the Sahara and diatomite aggregates from the Bodélé Depression in Chad. An aeolian abrasion chamber is used to reproduce the physical processes of aeolian abrasion and test the hypothesis that the breakdown of saltating diatomite flakes as they collide in saltation, and with the surface, is the most prolific mechanism of dust production (auto‐abrasion). This hypothesis is tested against the competing hypothesis that a hard, higher‐density quartz sand impactor is required to abrade fine‐grained sediments to generate dust. The results show that dust can be produced by a mixture of saltating diatomite and quartz sand particles. However, quartz sand is not required for saltating aggregates to produce dust. Indeed, these results, which used a mixture of very coarse‐grained aggregate (1 to 2 mm diameter) with fine quartz sand, indicate that the addition of quartz sand can decrease dust production. For a very coarse aggregate (1 to 2 mm), a pure diatomite aggregate produced the most dust, although using a coarse‐grained aggregate (0·5 to 1·0 mm) with a mixture of 20% quartz and 80% aggregate was found to produce the most dust overall. The results of this study confirm the auto‐abrasion hypothesis for the breakdown of diatomite particles in the Bodélé Depression, which is the single biggest source of atmospheric mineral dust on Earth.  相似文献   

A conceptual model of wind erosion of soil surfaces by saltating particles     

M. A. Rice  I. K. McEwan  C. E. Mullins 《地球表面变化过程与地形》1999,24(5):383-392

A conceptual model is described for the prediction of wind erosion rates dependent on the distribution of impact energy delivered to the surface by saltating grains, P[Ei], and the distribution of local surface strength, P[Es]. Methods are presented for the measurement of both distributions and consequent loss of material from the bed. It is concluded that saltating sand grains can rupture weak crusts under even moderate wind conditions, and that the rate of erosion will depend on the shape of the distribution tails. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献