Experimental analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry （PDA） in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the X^2-test for these probability distributions, that the probability density functions （pdf＇s） of the sand particles＇ lift-off and incident velocities as well as their vertical com- ponents are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions, These pdf＇s depend on not only the sand particle diameter but also the wind speed.

Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.

Dynamic Characteristics Analysis on Wind-Blown Sand Ground under Dynamic Compaction Vibration

In the 6000 kN·m energy level dynamic compaction on Inner Mongolia wind-blown sand foundation treatment process, the dynamic characteristics and dynamic response are measured. Vibration action time, vibration main frequency, peak acceleration and peak velocity are analyzed. The vibration acting time is very short, the vertical average vibration acting time increases obviously with distance increasing, and the horizontal average vibration time does hardly change. The main frequency of vibration is at 4.60 - 24.90 Hz, which depends on the soil properties and soil layer distribution. The peak acceleration and peak velocity space distribution are similar. The maximum of horizontal acceleration peak is close to vertical velocity peak, and is near to 51 g under rammer. The maximum of horizontal velocity peak is close to vertical velocity peak, and is near to 54 m/s under rammer. The peak acceleration and velocity are rapidly attenuated, but the vertical peak acceleration and peak velocity are slowly attenuated than horizontal direction. The effective treating depth arrives 13 m for wind-blown wind, peak acceleration is 1.8 g or so, and peak velocity is 2.1 m/s or so. Horizontal treating range is 2.6 times of rammer diameter, and vertical treating range is 5.65 times of rammer diameter.

Prevention and management of wind-blown sand damage along Qinghai-Tibet Railway in Cuonahu Lake area

This paper analyzes the characteristics of climate, geology and geomorphology, vegetation, and sand dune distribution in the Cuonahu Lake area beside the Qinghai-Tibet Railway. The types and causes of railway blown-sand hazards are discussed, and the effectiveness of various sand-controlling measures is assessed. From the perspective of integrated management, a sand-controlling system that combines several engineering measures, including nylon net sand barriers, concrete sand barriers, movable-board sand barriers, sand interception ditches, gravel/rock cover, film sandbags, and permanent vegetation is most beneficial.

Electromagnetic scattering of charged particles in a strong wind-blown sand electric field

Some field experimental results have shown that the moving sands or dust aerosols in nature are usually electrified,and those charged particles also produce a strong electric field in air, which is named as wind-blown sand electric field.Some scholars have pointed out that the net charge on the particle significantly enhances its electromagnetic(EM) extinction properties, but up to now, there is no conclusive research on the effect of the environmental electric field. Based on the extended Mie theory, the effect of the electric field in a sandstorm on the EM attenuation properties of the charged larger dust particle is studied. The numerical results indicate that the environmental electric field also has a great influence on the particle's optical properties, and the stronger the electric field, the bigger the effect. In addition, the charged angle, the charge density, and the particle radius all have a specific impact on the charged particle's optical properties.

Probability of rebound and eject of sand particles in wind-blown sand movement

When incident particles impact into a sand bed in wind-blown sand movement, rebound of the incident particles and eject of the sand particles by the incident particles affect directly the development of wind sand flux. In order to obtain rebound and eject lift-off probability of the sand particles, we apply the particle-bed stochastic collision model presented in our pervious works to derive analytic solutions of velocities of the incident and impacted particles in the postcollision bed. In order to describe randomness inherent in the real particle-bed collision, we take the incident angle, the impact position and the direction of resultant action of sand particles in sand bed on the impacted sand particle as ran- dom variables, and calculate the rebound and eject velocities, angles and coefficients （ratio of rebound and eject velocity to incident velocity）. Numerical results are found in accordance with current experimental results. The rebound and eject liftoff probabilities versus the incident and creeping velocities are predicted.

Influence of Golmud-Lhasa Section of Qinghai-Tibet Railway on Blown Sand Transport

The Qinghai-Tibet Railway(QTR) passes through 281 km of sandy land, 11.07 km of which causes serious sand damage to the railway and thus, the control of blown sand is important for the safe operation of the railway. Construction of the railway and sand prevention system greatly changed the blown sand transport of the primary surface. Effective and feasible sand-control measures include stone checkerboard barriers(SCBs), sand fences(SFs), and gravel coverings. This study simulated the embankments, SCBs and SFs of the QTR in a wind tunnel, and analyzed their respective wind profile, sand deposition, and sand-blocking rate(SBR) in conjunction with field data, aiming at studying the influence of Golmud-Lhasa section of the QTR and sand prevention system on blown sand transport. The results of wind tunnel experiments showed that wind speed increased by 67.7%–77.3% at the upwind shoulder of the embankment and decreased by 50.0%–83.3% at upwind foot of embankment. Wind speed decreased by 50.0%–100.0% after passing through the first SF, and 72.2%–100.0% after the first row of stones within the first SCB grid. In the experiment of sand deposition, the higher the wind speed, the lower the SBR of SCB and SF. From field investigation, the amount of sand blocked by the four SFs decreased exponentially and its SBR was about 50.0%. By contrast, SCB could only block lower amounts of sand, but had a higher SBR(96.7%) than SF. Although, results show that SFs and SCBs along the Golmud-Lhasa section of the QTR provide an obvious sand blocking effect, they lead to the deposition of a large amount of sand, which forms artificial dunes and becomes a new source of sand damage.

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert, China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions： no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m（i.e., 13 H, where H denotes the fence height） downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.

乌兰布和荒漠绿洲风沙特性及防护林防护效应

农田防护林在保持水土及土壤风蚀防控方面发挥着重要作用。为了探究真实大气环境下绿洲防护林体系的防风阻沙效益,以乌兰布和荒漠绿洲防护林为研究对象,利用位于荒漠绿洲过渡带和绿洲的近地面沙尘观测塔监测的2019—2020年不同高度处的风速、风向和沙尘数据,分析荒漠绿洲过渡带和绿洲的风沙分布统计特性。结果表明:荒漠绿洲过渡带和绿洲主导风向为东北和西南方向,2区域内平均风速均随观测高度增加逐渐增大;从荒漠绿洲过渡带至绿洲,受防护林体系的影响,平均风速整体减弱,≥4~8 m/s的中风速和≥8 m/s的高风速样本比例平均减少约8.8%和7.8%;荒漠绿洲过渡带和绿洲月最大平均风速多出现在夏秋2季以及春季末,且月最大平均风速与平均风速均值呈线性关系;2区域沙通量随着高度的增加逐渐减少,受防护林带影响同观测高度水平沙通量和垂直沙通量分别减少65%和36%;输沙方向整体朝东和东南偏东方向,该方向在绿洲受观测高度影响较小,在荒漠绿洲过渡带不同高度输沙方向会产生差异,输沙势从荒漠绿洲过渡带至绿洲总体降低。防护林体系对区域范围内的风沙活动影响明显,能够减轻风蚀所带来的水土流失,对绿洲可持续发展具有重要价值。

含沙量对地面光伏阵列的气动载荷研究

沙粒体积分数是风沙环境中影响光伏板及其承载结构使用寿命的重要因素之一,光伏板表面压力和倾覆力矩预测对光伏阵列的安装与设计,以及挡风沙结构的设计都有十分重要的意义。以安装倾角为25°,4×4方阵形式的光伏阵列为研究对象,采用欧拉双流体模型探究不同浓度对光伏板表面及其周围流场结构和倾覆力矩的影响规律。结果表明,不同沙粒浓度下,光伏板上表面的风沙压力变化分布情况基本相同,而随着入口处沙粒体积分数的增大,光伏板上表面同一区域的风沙压力不断增大。除第二排光伏板,其余光伏板倾覆力矩随入口处沙粒体积分数增大而增大,且第一排倾覆力矩最大。研究工作可为荒漠地区光伏阵列的设计和安装提供一定的理论依据。

和田-若羌铁路“七带一体”综合防沙技术

和田—若羌铁路(和若铁路)位于世界第二大流动沙漠塔克拉玛干沙漠南缘,剧烈的风沙活动对其中409.19 km线路的运营安全造成重大威胁,因此风沙治理成为和若铁路成功建设和安全运营的关键。该文首先调查和归纳和若铁路沿线的风沙危害现状,随后对铁路建设过程中摸索总结的“七带一体”的综合防沙技术进行介绍,实现建设期沙害不上道的目标,目前植物综合成活率达到85%以上,植株平距高度在1.0~1.5 m,为和若铁路的安全运营保驾护航。相关工作和成果能够指导类似工程的设计、施工及管理,为国家在项目审批中的决策提供依据。

南疆农作物风沙危害理论及防治研究进展

南疆沙漠边缘的绿洲农区是我国风沙危害最严重的地区之一,特别是棉花苗期和果树花果期,风沙造成幼苗死亡、茎倒枝折、落花落果,经济损失巨大,因此,开展南疆农作物风沙危害及防治研究具有重要的现实意义和区域经济价值。本文通过回顾农田的风沙流结构特征,梳理了风沙对农作物的2种危害形式,概述了农作物风沙防护机制及防治措施研究现状;最后,指出了农作物风沙危害研究中存在的问题,基于南疆的农作物类型及风沙环境特征,提出了未来南疆农作物风沙危害及防治研究重点并对未来研究进行了展望。

风沙流环境地表剪切力测量

地表剪切力是风沙运动的关键驱动力,在风沙运动研究中非常重要,但目前针对风沙流环境地表剪切力的实验测量却较为匮乏,已经成为风沙运动研究深入发展的瓶颈。本文介绍了一种基于热膜技术的适用于风沙流环境地表剪切力精确测量的方法,使用热膜传感器和二维热线探头对净风条件下的地表剪切力进行了测量,结果显示:热膜传感器对地表剪切力有较好的响应,其与二维热线探头对摩阻风速的测量结果相差小于6.6%。热膜传感器对方柱绕流条件下地表剪切力的测量结果与OpenFOAM数值模拟结果具有较好的一致性,进一步证明了热膜传感器测量地表剪切力的可行性。热膜传感器的沙粒撞击实验结果表明:沙粒撞击对热膜信号的影响可以忽略,在风沙流环境中可以采用热膜传感器对地表剪切力进行有效测量。基于该技术测量了风沙流环境地表剪切力沿流向的空间分布特征,采用实测方式获得了风沙流环境地表剪切力的空间分布规律。

干枯植被覆盖对公路沿线地表风沙流结构的影响

[目的]以内蒙古S105草原公路沿线地表为研究对象,探讨挟沙风作用下干枯植被覆盖度对风沙流结构的影响,旨在为防治公路两侧土壤风蚀提供理论参考依据。[方法]采用风洞模拟试验,在0%,20%,40%和50%覆盖度水平下测定输沙率。[结果]在挟沙风作用下,输沙率随干枯植被覆盖度的增大而递减,最大输沙率点的高度层不断上升。覆盖度为0%时,输沙率随高度的增加呈指数函数规律降低;覆盖度为20%,40%和50%时,输沙率随高度的增加呈递减→递增→递减→趋于平缓的变化规律;在85 mm高度以下符合多项式函数关系,85 mm高度以上符合指数函数关系。随覆盖度的增大总输沙量递减,最大抗风蚀效率达65.73%。[结论]干枯植被覆盖显著影响地表风沙流结构,可削弱挟沙风侵蚀力,是抑制公路沿线地表土壤风蚀沙化的有效措施。

无定河上游流域水体微塑料污染现状与分布特征

调查了黄河一级支流无定河上游干流和纳林河、海流兔河、榆溪河、芦河等支流水体微塑料的丰度和分布情况.结果显示:无定河上游流域水体微塑料的平均丰度为15.58n/L,范围2.5~35.63n/L.微塑料类型丰富,占比依次为PEG(62.96%)、PE(6.17%)、PPS(3.09%)、4-vinylbiphenyl(2.78%)、PCTG(2.47%)、PS(2.16%)、PTFE(2.16%)、PPSU(1.85%)、PMMA(1.54%)、其他(14.81%).超过96%的微塑料小于1mm,极易进入生物体富集.形状以片为主,其次是薄膜和颗粒状;大部分为透明或棕色,其他颜色占比约25%.基于微塑料的源特定分类体系,初步判定微塑料主要来源于农用地膜、个人洗护用品.结果表明无定河上游流域水体微塑料整体处于轻度污染水平.有毒有害塑料的滥用尤为需要引起关注.无定河上游流域位于毛乌素沙漠东南部的风沙滩地,其微塑料研究一方面揭示了风沙滩地水体微塑料的赋存现状和潜在污染风险;另一方面提供了一个典型案例,即以微塑料的视角,科学认识沙漠地区的城市发展和农业生产对水体环境的影响.

挡风墙周围风沙流运动特性SPH数值分析

光滑粒子流体动力学方法(Smoothed Particle Hydrodynamics, SPH)是一种纯拉格朗日、无网格的流体模拟方法。首先对SPH法的基本原理、核函数构造及控制方程离散方法、边界处理及邻域粒子搜索算法、时间积分等作了具体介绍。通过Linux平台编写的二维SPH程序较好地模拟了挡风墙周围风沙两相流的运动特性。仿真结果再现了沙障附近积沙的复杂物理现象:挡风墙周围积沙量以挡风墙为中心,呈“正态性”分布,中间多,两边少。且挡风墙存在时,对风速的阻挡作用随挡风墙高度增加而减小,水平风速超过其垂向高度后逐渐恢复至无挡风墙时的风场状态。表明风沙流运动过程中挡风墙对跃移沙粒和来流风具有明显的阻挡效应,与已有相关模拟结果相符,验证了SPH数值模拟方法的有效性。并为SPH方法在风沙两相流领域的进一步拓展和应用奠定了基础。

循环荷载下风积沙填料的临界动应力

针对我国沙漠铁路中风积沙填料在列车动荷载作用下动力性能不明确的问题,研究风积沙填料在列车循环荷载作用下的变形特性,考虑动应力幅值、含水率和围压的影响进行了风积沙填料动三轴试验;分析了风积沙试样累积塑性变形的发展规律,建立了风积沙塑性变形行为判定标准,获得了风积沙填料的临界动应力。结果表明:风积沙试样的累积塑性应变与循环振次的关系曲线可划分为稳定型、临界型和破坏型三种类型;风积沙累积塑性应变速率与循环振次呈幂函数关系,得出了风积沙填料塑性行为判定标准;以安定准则为破坏判据,在风积沙填料塑性行为划分基础上,引入静强度参数反映土体自身物理性质对动应力水平的影响,得到了考虑动应力幅值、含水率及围压的风积沙填料临界动应力经验公式。

风力机叶片涂层冲蚀磨损实验装置的设计

风力发电机叶片在风沙环境中运行时会受到挟沙风的冲蚀,导致叶片表面涂层损毁并且降低叶片使用寿命,同时也增加叶片的维护成本。为了探究风力机叶片受挟沙风冲蚀磨损情况,研制一种涂层冲蚀磨损实验装置,该实验装置以压缩空气为动力,通过压缩空气气管接通气源。压缩空气在冲蚀管中建立工作压力,在冲蚀管内完成沙料和压缩空气充分混合,形成高速运动的挟沙风;再利用PLC控制步进电动机转速,通过螺旋推进器进行输沙率控制,由冲蚀管喷嘴喷出,喷射到风力机叶片模型表面对其进行冲蚀磨损实验。该冲蚀装置可实现多种冲击风速、携沙量、冲击角度的多工况磨损实验,能够提供较为精确的实验数据。

A laboratory test of the electrification phenomenon in wind-blown sand flux

The measured data in the wind-tunnel tests show that the wind-blown sand particles acquired a negative charge when their diameters are smaller than 250 μm and positive charge when their diameters are larger than 500 μm, which confirms Latham’s assumption that the large particles in wind-blown sand flux acquired positive charge while negative charge developed on small ones. In the meanwhile, the measured data also show that the average charge-to-mass ratio for wind-blown sand particles decreases with the increase of the particle diameter and the wind velocity, and increases with the rise of height. The electric field in wind-blown sand flux is mainly formed by the moving charged sand particles. Its direction is vertical to the Earth’s surface and upward, which is opposite to that of the fair-weather field. The electric field increases with wind velocity and height increasing. These experimental results will lay the foundation for developing the theoretical analysis of the electrification phenomenon in

风积沙自密实混凝土充填材料配比方案研究

膏体充填开采是煤矿开采技术的重要组成部分,充填材料是膏体充填技术的核心,对充填质量的优劣、充填成本的高低起着决定性作用。如何高效低成本的达到充填效果一直是困扰煤矿的工程难题。近年来,有学者选取风积沙作为充填材料进行了研究,并取得了不错的效果,加之新疆地区拥有较大面积的沙漠,风积沙廉价易得,因此,本文采用对比试验的方法对风积沙自密实混凝土充填材料配比进行设计,探究水泥、粉煤灰、水及风积沙四个因素共同作用下对自密实充填体的力学及工作性能影响规律,确定充填材料的最佳配比。