Effects of Desertification Control Project Based on Windbreak System in Daxing County, Beijing

Windbreak system consisting of the forms of net, belt, sheet and point, has improved local eco environment greatly and promoted the level of social economy and local people's living. The result of environment impact assessment shows that the quality of eco environment has been improved obviously and the impact process is mainly positive after building of windbreak system in Daxing County of Beijing, a dry sub humid region. Effects of windbreak system and their environmental impacts are analyzed scientifically and reasonably in this paper. The study will enrich the theory of environment impact assessment and extend the scope of research, and will provide experience for the construction of windbreak system in the region.

Effects of sand-fixing and windbreak forests on wind flow:a synthesis of results from field experiments and numerical simulations

Sand-fixing and windbreak forests are widely used to protect or/and improve the ecological environments in arid and semi-arid regions. A full understanding of wind flow characteristics is essential to arranging the patterns of these protective forests for enhancing the effectiveness. In this study, the wind velocity over the underlying surface with sand-fixing forests and windbreak forests at the heights of 1–49 m was monitored from two 50-m high observation towers in an oasis of Minqin, Gansu Province of China. The wind velocities were simulated at different locations over these protective forests between those two towers by a two-dimensional Computational Fluid Dynamics（CFD） model. The results showed that at the heights of 1–49 m, the wind velocity profiles followed a classical logarithm law at the edge of the oasis and a multilayer structure inside the oasis. With increasing number of sand-fixing forest and windbreak forest arrays, the wind velocity at the heights of 1–49 m generally decreased along the downstream direction of the prevailing wind. Specifically, below the height of windbreak forests, the wind velocity decelerates as the airflow approaches to the windbreak forests and then accelerates as the airflow passes over the windbreak forests. In contrast, above the height of windbreak forests, the wind velocity accelerates as the airflow approaches to the windbreak forests and then generally decelerates as the airflow passes over the windbreak forests. Both the array number and array spacing of sand-fixing and windbreak forests could influence the wind velocity. The wind protection effects of sand-fixing forests were closely related to the array spacing of windbreak forests and increased with the addition of sand-fixing forests when the array of the forests was adequately spaced. However, if the array spacing of windbreak forests was smaller than seven times of the heights of windbreak forests, the effects were reduced or completely masked by the effects of windbreak forests. The results could offer theoretical guidelines on how to systematically arrange the patterns of sand-fixing and windbreak forests for preventing wind erosion in the most convenient and the cheapest ways.

Dynamic behaviors and mitigation measures of a train passing through windbreak transitions from ground to cutting

In this paper,the effects of a right-angle windbreak transition(RWT)from the flat ground to cutting on train aerodynamic and dynamic responses were investigated,then a mitigation measure,an oblique structure transition(OST)was proposed to reduce the impact of RWT on the train aerodynamic and dynamic performance.The results showed that in the RWT region,the airflow was divided into two parts.One part of the airflow induced a strong backflow in the flat ground position,and the other part of the airflow induced a strong backflow in the cutting position.Therefore,there were two lateral impacts on the train.For the head car with the OST,the drop ratios of the peak-to-peak values compared with RWT were 47%,40%,and 52%for the side force coefficient C_(Fy),lift force coefficient C_(Fz) and overturning moment coefficient C_(Mx),respectively.For the peak-to-peak value of the dynamic parameters,the drop ratios of OST compared with RWT were all larger than 50%.The maximum dynamic overturning coefficients for RWT and OST were 0.75 and 0.3,respectively.

Evaluation on Regional Ecological Benefits of Windbreak Systems

This paper studied how dynamically to evaluate regional ecological benefits of windbreak systems in a county scale. Data of air temperature. humidity. wind speed, crop yield and forest cover percentage were investigated and collected in some of counties of Heilongjiang Province, where windbreak systems were established in the last thirty years. Through analysis, an evaluation index system estimating regional ecological benetits of windbreak systems was set up, which consists of both a vegetation index system and a climate index systeln. The former includes a forest cover percentage index and a crop yield index; the later does three variable indexes of wind speed, air temperature and humidity. An integrated regional ecological benefit index.was developed through combinations of some coined evaluation indexes from the evaluation system.And to take Zhaozhou County and Anda County as a case study, the regional ecological benetits since establishment of windbreak systems of the two counties were evaluated dynamically using the integrated index.

Numerical Analysis of Different Nose Shapes on the Train Aerodynamic Performance at a Windbreak Transition under Crosswinds

Based on the Unsteady Reynolds-Averaged Navier-Stokes (URANS) method, this paper studied the effect of the nose shape on the aerodynamic performance when the high-speed train subjected to a windbreak transition under crosswinds. The windbreak transition generated by the irregular terrain from the flat ground to the cutting. The results showed that with the height of the front window increased from Z ? 2 to Z + 2 (the dimensionless height), the side force coefficient Cy and rolling moment co-efficient Cmx increased by 26% and 27% for the head car, respectively. The flow structures around the lower front window were smoother than that around the higher front window. The flow structures in the higher front window resulted in more considerable positive pressure on the windward side (WWS) and top of the nose region.

ECOLOGICAL LANDSCAPE EFFECTS OF WINDBREAK SYSTEMS IN DESERT ZONE OF WESTERN CHINA

This paper, by applying the theories of landscape ecology, illustrates the role and mechanism of windbreak system in the establishment and maintenance of oasis ecosystem on the basis of systematic analysis of characteristics and ecological crises of China's desert, and especially of desert zone in western China. Furthermore, direct economic benefits are summarized.

A PRELIMINARY SPECTRUM ANALYSIS ON TURBULENCE IN LEESIDE OF WINDBREAKS

The spectrum characteristics of turbulence such as period of fluctuation, frequency and amplitude of oscillation were discussed by using the method of spectral analysis of turbulence in this paper. The results show that the spectrum density in the range of low frequency is sharply variance with the distance from the windbreaks, but it follows the power index law of -5 / 3 and satisfies the theory of local isotropic turbulence in the range of high frequency. It also shows by connecting with Eulerium autocorrelation analysis that there are small scale,high frequency and short period of turbulence near the lecsidc of windbreaks,but often large scale, low frequency and long period of turbulence far from the windbreaks.

WINDBREAKS FOR SAND DUNE FIXATION IN JILIN PROVINCE

There are 0.78 million hm2 of sand dune areas in Jilin Province. The effects of two types of windbreaks. shelterbelts and small areas ofartdicial forests, on sand dune fixation were discussed. The temperature, humidity and reduced situation of wind speed in the two types of windbreaks wer systematically studied.

THE DISTRIBUTION CHARACTERISTICS OF TURBULENCE ON LEESIDE OF WINDBREAKS

The distributive characteristics of turbulence, turbulent velocity, turbulent intensity and Reynolds stress, in horizontal and vertical direction on leeward side of windbreak were discussed in this paper. The results show that all the three kinds of parameters of turbulence have the similar distributive patterns in lee, their peaks were around 10H for horizontal and Z/ H = 1 for vertical. The windbreak is important barrier to affect the structure and distribution of wind speed and turbulence. Porosities of windbreaks could alter the patterns of turbulence, therefore, affect the abilities and functions of windbreaks.

Effects of Different Wind Speeds behind Windbreak Wall of Fattening Cattle Farm on Farm Environment and Performance of Beef Cattle in Zhangye District

[Objective]The paper was to study the wind-reducing effect of windbreak wall at different sheltering distances and the effects of wind speed on cattle performance.[Method]The 40 cattle with insignificant difference in initial weight were randomly distributed in four selected stalls,and were divided into two groups according to the distance between stalls and windbreak wall to measure their daily gain.According to the actual conditions and weather conditions of fattening cattle farm,the wind speed,temperature and other environmental indexes of measuring point and heat production of beef cattle were carried out field measurement and analysis.[Result]The windbreak wall in fattening cattle farm reduced the wind speed by 40%-70%within a horizontal distance of 10 times of the wall height at a height of 1.2 m.The best sheltered area behind windbreak wall was 2-4 times of the height of windbreak wall.Within the distance of 6 times of the wall height,the wind speed reduction effect was obvious and the maximum reduction rate reached 70%.With an external WCI of-15.61 and average beef cattle weight of 480 kg,the WCI of fattening cattle farm equipped with windbreak wall reached-9.00,and the heat loss reduced by each cow was 3.31 MJ/h.Meantime,due to the difference in distance from windbreak wall,the daily gain difference of beef cattle was 0.15 kg/head day,but the difference was not significant(P>0.05).

Design of Tall Cable-Supported Windbreak Panels

The design and construction of tall and slender steel structures is always challenging. This paper discusses several design aspects (structural information, analysis methods, applied loads, cost optimisation) and a case study regarding the design and construction of 10-m-tall windbreak panels for a Greek electricity producer. The purpose of the panels is to reduce wind turbulence and improve the performance of the electricity producer’s air-cooled condenser. In this case, the main wind load acts in the longitudinal direction, with friction inducing only a small amount of wind load in the transverse direction. The steel columns are constructed from 10-m-tall hot-rolled IPE 270 (S235) cross-sections, and are supported by cables in the longitudinal direction and bracing systems in the transverse direction. Concrete anchorages and concrete footings are used for the cables and steel columns, respectively. System optimisation is investigated in terms of the steel weight, cable length, and overall cost, and practical issues are explained regarding technical decisions. Furthermore, the construction details, construction methods, and cost estimation are discussed.

Analysis of the Application of Windbreak and Sand Fixation Technology in Desert Roads

In order to solve the problems in the construction of desert roads and improve the quality of desert roads in China,this paper discusses the current windbreak and sand fixation technologies in desert areas in China,and puts forward relevant suggestions and corresponding solutions for each problem.This paper is written with hopes of contributing to the development of windbreak and sand fixation technologies in China as well as the development of the economy,society and environment in China's deserts.

Utilizing sediment grain size characteristics to assess the effectiveness of clay–sand barriers in reducing aeolian erosion in Minqin desert area,China

The clay–sand barriers in Minqin desert area,China,represent a pioneering windbreak and sand fixation project with a venerable history of 60 a.However,studies on evaluating the long-term effectiveness of clay–sand barriers against aeolian erosion,particularly from the perspective of surface sediment grain size,are limited and thus insufficient to ascertain the protective impact of these barriers on regional aeolian activities.This study focused on the surface sediments(topsoil of 0–3 cm depth)of clay–sand barriers in Minqin desert area to explain their erosion resistance from the perspective of surface sediment grain size.In March 2023,six clay–sand barrier sampling plots with clay–sand barriers of different deployment durations(1,5,10,20,40,and 60 a)were selected as experimental plots,and one control sampling plot was set in an adjacent mobile sandy area without sand barriers.Surface sediment samples were collected from the topsoil of each sampling plot in the study area in April 2023 and sediment grain size characteristics were analyzed.Results indicated a predominance of fine and medium sands in the surface sediments of the study area.The deployment of clay–sand barriers cultivated a fine quality in grain size composition of the regional surface sediments,increasing the average contents of very fine sand,silt,and clay by 30.82%,417.38%,and 381.52%,respectively.This trend became markedly pronounced a decade after the deployment of clay–sand barriers.The effectiveness of clay–sand barriers in erosion resistance was manifested through reduced wind velocity,the interception of sand flow,and the promotion of fine surface sediment particles.Coarser particles such as medium,coarse,and very coarse sands predominantly accumulated on the external side of the barriers,while finer particles such as fine and very fine sands concentrated in the upwind(northwest)region of the barriers.By contrast,the contents of finest particles such as silt and clay were higher in the downwind(southeast)region of the sampling plots.For the study area,the deployment of clay–sand barriers remains one of the most cost-effective engineering solutions for aeolian erosion control,with sediment grain size parameters serving as quantitative indicators for the assessment of these barriers in combating desertification.The results of this study provide a theoretical foundation for the construction of windbreak and sand fixation systems and the optimization of artificial sand control projects in arid desert areas.

防风抑尘网减风抑尘效果数值模拟研究

依托洋浦港三期散货码头工程,对35个堆垛的防风(抑尘)网各布置方案进行数值模拟,计算其在布置防风(抑尘)网前后堆场的起尘量、敏感点的TSP浓度值及降尘量,并通过比选推荐出经济、合理的防风(抑尘)网布置方案。通过数值模拟表明,防风(抑尘)网的减风效果与网高的设置有关,防风(抑尘)网的抑尘效果与布置有关。本项目的建设和研究成果可供国内同类港口工程借鉴,对我国环保事业的发展起到推动作用。

和田地区农田防护林更新存在问题的研究——以洛浦县为例

选择和田地区特定区域,研究农田防护林树种组成、混交情况、年龄结构等,分析其经营现状及存在的问题.结果表明：洛浦县农田防护林存在混交林比例过低,仅占防护林总面积的11.29％;林龄结构不合理,大多集中于7～16年；防护林树种少、经济价值低；林网规格与保护对象不适应等现实问题.并针对问题提出加强宣传和指导营造混交林；利用防护林防护成熟、工艺成熟和经济成熟期的时间差调整防护林林龄结构；引入夏橡、水曲柳、黑核桃等经济价值高的树种营建混交林带,并积极营建生态经济型防护林；根据保护目标植物适时调整林网大小等解决对策.

不同组合间距的尼龙阻沙网积沙形态特征对比

在塔克拉玛干沙漠腹地垄间平沙地,布设了两条尼龙阻沙网水平组合防沙实验,组合间距分别为2H、5H、10H、15H(H为阻沙网高度),一个风季中对实验设置的地形及纵断面蚀积量进行了动态观测。结果表明:(1)各尼龙阻沙网组合形成有规律的地表蚀积空间分布格局:形成以阻沙网为核心的积沙区,其上下风侧分布有较稳定的风蚀区,两条阻沙网之间存在临时的风蚀区。(2)在阻沙网前后形成与阻沙网高度相近的积沙体,在第一条阻沙网上风侧区域,积沙厚度与水平距离呈指数函数关系,在阻沙网背风侧,积沙厚度与水平距离呈二次函数关系。(3)2H和5H积沙体纵断面呈单峰状,风季中后期形似"几"字形,而10H和15H呈双峰状,风季中后期形似"M"字形。(4)阻沙网组合间距越小,积沙分布就越集中,形体越高大,反之则越分散,风季末阻沙网积沙体地形起伏度、平均坡降、积沙体积比、积沙断面面积轮廓比大小排序均为2H>5H>10H>15H。(5)阻沙网积沙体积具有随阻沙网间距增大而降低的趋势,观测断面最大积沙体积5HH>2H>15H>10H,5H、2H、15H分别较10H大13.20%、12.34%、3.78%,可见,5H防沙效果最优。

林网下垫面稳定大气近地面层温、湿和风速廓线相似性及通量特征

本文根据在林网下垫面测量的温、湿和风速梯度资料,分析了温、湿和风速廓线的相似性及通量特征。结果表明:在林网下垫面弱稳定大气近地面层中(0.1<Ri<0.25),温、湿和风速廓线符合Monin—Obukhov相似理论所予期的对数线性分布规律。相似函数P值在1附近,在Ri<0.25,P值变化不明显,Ri>0.25时,随Ri增大而增大。廓线参数β_u,β_?和β_w不是常数,而是稳定度参数Ri和L的函数。在Ri=0.25和L=20米附近廓线参数出现间断,两边遵循不同的变化规律。当Ri>0.25时,湍流交换减弱,感热和潜热通量的变化趋于稳定。

直接空冷机组夏季度夏措施及发展趋势

直接空冷机组具有节水的优点,在我国北方地区得到了广泛的应用。分析直接空冷机组夏季运行存在的主要问题,提出度夏措施及可行性的解决方案。结果表明,高温环境、自然大风、凝汽器管束脏污、真空泵工作水温偏高是影响直接空冷机组夏季运行背压高的主要因素。设置喷淋装置、延伸挡风墙、加装导流装置和防风网、提高散热器的冲洗质量是保证直接空冷机组夏季高温季节安全经济运行的重要措施。

葡萄防雹、防风网防风效果研究

本试验对葡萄防雹网和防风网的防风效果进行了初步研究,并对不同网眼规格的防雹网内受风沙危害的葡萄叶片破损率进行了调查。结果表明,防风网的阻风能力随着网外风速的变大而增强。当网外风速在2～3m/s时,防风网防护距离为30m。当网外风速为3～4m/s时,防风网的防护距离为40m。防雹网的阻风能力也存在随网外风速变大而增强的趋势,并且不同网眼规格的防雹网内葡萄叶片破损率与未架网园存在显著差异,架设网眼边长为1.0～1.2cm的防雹网的葡萄园叶片受风沙危害的破损率比未架网园降低50%左右。

防风网结构优化及粉尘颗粒运动数值模拟

应用流体力学计算软件FLUENT对25%开孔率下不同形式的新型导流板式防风网流场进行了模拟。比较了常规直立式防风网和不同导流板弯曲长度和弯曲角度组合的导流板式防风网后物料堆垛表面的风速、湍流强度以及剪切应力的分布规律,并用离散相模型预测了网后堆垛表面粉尘颗粒的运动轨迹。研究结果表明:导流板式防风网减小了来流风对堆垛的直接作用,提高了防风抑尘水平。