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.

The effects of human activities on windbreak and sand fixation services in Inner Mongolia grasslands from 2000 to 2020

Windbreak and sand fixation services(SR)provided by grasslands are a joint result of climate change and human activities.Series of grassland protection measurements have been successively implemented on Inner Mongolia grasslands since 2000,but their effects on SR remains unclear.Based on satellite-derived vegetation dynamics and the Revised Wind Erosion Equation(RWEQ)model,this paper developed a method for quantitatively separating the impact of human activities on SR and revealed the contribution of human activities to SR in the Inner Mongolia grasslands from 2000 to 2020.In 2020,the actual sand fixation(SRA)of Inner Mongolia grasslands was 12.50 t·ha^(-1),spatially characterized as lower in the eastern and western parts,which was dominated by the sparse vegetation coverage and the low potential wind erosion respectively,while higher in the central part,due to the grassland vulnerability.The human-driven sand fixation(SRH)of Inner Mongolia grasslands changed from–1.28 t·ha^(-1)to–0.14 t·ha^(-1)from 2000 to 2020,indicating human activities inhibited SR,but the inhibition was gradually weakened.In semidesert and meadow steppes,the SRHchanged from–3.00 t·ha^(-1)to 0.00 t·ha^(-1)and–0.16 t·ha^(-1)to 0.00 t·ha^(-1),respectively,which showed that the effect of human activities changed from inhibition to promotion.However,it should be noted that human activities still inhibited the SR in typical steppes.The results implicated that grassland ecological protection should pay much more attention to reasonable use of vulnerable typical steppes.Future grassland use requires quantitative evaluation on the effects of human activity for precise monitoring and sustainable management.

An Application of the Shark Skin Denticle Geometry for Windbreak Fence Design and Fabrication

Windbreak fences in open and urban areas can be used to effectively reduce the wind velocity. In this paper we examine how the geometrical shape of the windbreak fence can optimally mitigate wind velocity. We propose an approach for windbreak fence design based on a bionic parametric model of the shark skin denticle geometry, which improves the reduction of the wind velocity around and behind the windbreak fences. The generative model was used to estimate improvements by variations in the parameters of the fence panel＇s geometrical shape, inspired by shark skin denticles. The results of the Computational Fluid Dynamics （CFD） analysis indicates that the fence surface inspired by shark skin performs much better than both flat and cor- rugated surfaces. Taking into account the complex geometry of the surface inspired by shark skin denticles, we propose a fab- rication process using an expanded polystyrene foam （EPS） material, created using an industrial robot arm with a hot-wire tool. Creating EPS moulds for the shark skin denticle panels allows for a richer variety material to be used in the final design, leading both to higher efficiency and a more attractive design.

Enhancement of Thermo-Flow Performances by Windbreakers for Two-Tower Indirect Dry Cooling System

The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers.The exterior windbreakers are recommended to restrain the wind adverse effects in this paper.The macro heat exchanger model was adopted to simulate the heat exchange between circulating water and ambient air.The performances of natural draft dry cooling system(NDDCS)with and without exterior windbreakers were numerically studied.The pressure,velocity and temperature distribution of cooling air in wind angles of 0°,45°and 90°was obtained and presented.The results show that in all wind directions,the performances for lateral sector of towers with windbreakers are significantly improved,but the low-pressure zone appears unexpectedly for the rear sectors,which reduces the air flow rate.The cooling performances of the twin towers with or without windbreakers decrease at first but then recover with the wind velocity increasing.Besides,the optimal flow and heat transfer performances appear in the wind angle of 0°.The cooling performances can be significantly improved in all three wind directions due to windbreaker configuration.

Sudden flow induced by mountain ridges beside windbreaks in a railway and its mitigation measures

The impact of a mountain ridge(MR)on the wind speed distribution and flow structures along a railway,under crosswinds beside a windbreak at attack angles of 90◦and 105◦,is studied in this paper.Based on the observed flow field deterioration mechanism,mitigation measures are proposed and the corresponding effects are compared,from which the preferred mitigation scheme is determined.For the original MR,the wind speed coefficient U is larger than 1.2 in the range below the train height at both wind angles.With the implementation of the flow field mitigation measures,as the distance(L)increases from the MR to the windbreak,the wind speed decreases linearly for the 90◦wind angle and quadratically for the 105◦wind angle.When the mitigation measure with L/h=8.1(h is the train height)is adopted,the wind speed coefficient U fluctuates very slightly in the MR area,with−0.2<U<0.05 at both wind angles.Therefore,L/h=8.1 is recommended to protect the operation safety of trains travelling under strong crosswinds.

Floating forest:A novel breakwater-windbreak structure against wind and wave hazards

A novel floating breakwater-windbreak structure(floating forest)has been designed for the protection of vulnerable coastal areas from extreme wind and wave loadings during storm conditions.The modular arch-shaped concrete structure is positioned perpendicularly to the direction of the prevailing wave and wind.The structure below the water surface acts as a porous breakwater with wave scattering capability.An array of tubular columns on the sloping deck of the breakwater act as an artificial forest-type windbreak.A feasibility study involving hydrodynamic and aerodynamic analyses has been performed,focusing on its capability in reducing wave heights and wind speeds in the lee side.The study shows that the proposed 1 km long floating forest is able to shelter a lee area that stretches up to 600 m,with 40%–60%wave energy reduction and 10%–80%peak wind speed reduction.

基于多孔介质的高速铁路透风式挡风墙关键参数研究

合理的匹配参数是风区铁路沿线防风设施研究的关键问题。针对风区铁路沿线部分区段混凝土实心挡风墙出现的环境风越过挡风墙顶导致严重的弓网离线、无法正常升弓,危及铁路行车安全问题,提出改“堵”为“疏”,通过一定的透风率来调控挡风墙后的线路风场,从而为缓解上述现象提供一种新思路,其关键问题在于透风式挡风墙关键参数与防风效果的合理匹配。为此,基于多孔介质的自身特性,提出一种基于多孔介质的挡风墙风场新研究方法,将挡风墙透风率与防风效果的合理匹配问题转化为多孔介质的阻力系数与列车气动载荷的关系研究。首先,通过比较数值模拟结果与兰新高铁挡风墙风场现场试验结果,修正并验证数值模拟方法的准确性。然后,通过数值模拟研究进一步探究多孔介质阻力参数与挡风墙透风率之间的关系,获得风区铁路沿线透风式挡风墙关键参数最优区间。研究结果表明:可以采用多孔介质代替挡风墙几何进行挡风墙风场研究,能够显著提升研究效率;多孔介质的黏性阻力系数在挡风墙风场研究中可以忽略,多孔介质的惯性阻力系数与挡风墙的透风率呈幂函数关系;风区铁路沿线透风式挡风墙高度为3.5 m,透风率在24.4%~28.7%区间时,对一线、二线列车的防风效果最好。

大风区高速铁路路基双侧挡风墙周围沙粒沉积数值模拟研究

兰新高速铁路横穿多个大风区,对其安全运营造成严重影响。为降低强风对线路的危害,在大风区修筑大量防风构筑物,其中以路基挡风墙最为常见,挡风墙降低了风害的影响,但是带来严重的线路积沙问题。通过数值模拟研究不同风速下路基双侧挡风墙周围的流场特征,利用风产生的壁面剪切应力与沙粒剪切应力的比值确定地表沙粒沉积与侵蚀类型。研究发现,气流在两道挡风墙之间分别形成一个顺时针涡流和一个逆时针涡流,在第二道挡风墙背风侧形成一个顺时针大涡,随着来流风速增大,漩涡尺寸和涡流强度均在增大;由于涡流的存在,部分沙粒被卷走,路堤背风坡附近以及路基面上的沙粒沉积显著减少,当来流风速为24、30 m/s时,南北侧线路道床面均出现沙粒反向侵蚀;单双侧挡风墙的积沙规律对比结果表明,设置双侧挡风墙时,线路积沙显著减少。研究揭示了大风区铁路双侧挡风墙周围路基面上的沙粒沉积规律,对未来风区铁路的防护建设具有指导意义。

琵琶柴的防风固沙作用数值模拟

植物固沙是北方干旱、半干旱区防治风沙灾害的重要措施之一,其中琵琶柴(Reaumuria soongorica)为荒漠区分布最广泛的半灌木,具有重要的应用价值。本文利用计算平台Fluent对琵琶柴植株附近的流场进行数值模拟,分析风速特征和积沙特征。结果表明:(1)在10 m·s^(-1)初始风速下,植株前后皆会形成涡流,其高度和强度与距植株远近有关,整体低于0.25 m。(2)数值模拟结果表明,气流水平方向速度的变化多呈“N”和“W”型曲线,而垂直方向的气流速度变化则为“V”型曲线。(3)在较低风速下,非生长季琵琶柴的阻风效能要优于生长季,株后防护距离4 m;当风速大于6 m·s^(-1)时,双排生长季琵琶柴株后风速降低幅度可大于94.45%。(4)琵琶柴具有良好的阻沙效果,在初始风速为6 m·s^(-1)时,大部分沙粒堆积在植株前后底部;当风速增至10 m·s^(-1)时,生长季琵琶柴阻沙良好,沙粒主要沉积在株后1.5~3 H,沙粒堆积高度小于0.1 m;当初始风速为15 m·s^(-1)时,生长季琵琶柴株后积沙主要分布在株后2~3.5 H,而非生长季琵琶柴沙粒堆积范围则在株后1~10 H。无论何种生长季琵琶柴均能有效降低风场内气流速度,并对气流所携带的沙粒具有良好的沉降作用,在植物治沙工程中起重要作用。