Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method ca...Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method can transform the reasonable matching problem of the porosity and windproof performance of the windbreak into a study of the relationship between the resistance coefficient of the porous medium and the aerodynamic load of the train.This study examines the influence of the hole type on the wind field behind the porosity windbreak.Then,the relationship between the resistance coefficient of the porous medium,the porosity of the windbreak,and the aerodynamic loads of the train is investigated.The results show that the porous media physical model can be used instead of the windbreak geometry to study the windbreak-train aerodynamic performance,and the process of using this method is suggested.展开更多
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 imp...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.展开更多
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 pa...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.展开更多
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 transitio...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.展开更多
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 investigat...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.展开更多
<div style="text-align:justify;"> 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-spee...<div style="text-align:justify;"> 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 <em>C</em><em><sub>y</sub><sup> </sup></em>and rolling moment co-efficient <em>C</em><sub><em>mx </em></sub>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. </div>展开更多
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 characte...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.展开更多
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 th...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.展开更多
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, humidit...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.展开更多
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,an...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.展开更多
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 ...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.展开更多
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...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.展开更多
[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...[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).展开更多
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 ca...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.展开更多
The embankment and the hill cut are conventional infrastructure scenarios along the railway line in windy regions.The windbreak walls with the same height are separately installed on them to guarantee the safety of tr...The embankment and the hill cut are conventional infrastructure scenarios along the railway line in windy regions.The windbreak walls with the same height are separately installed on them to guarantee the safety of train operation.However,due to the realistic terrain,the distances of windbreak walls on the embankment and hill cut from the railway centreline are not the same,generating a windbreak wall transition and causing a sudden change of the windproof performance,which contributes to the so-called'yawingphenomenon when the train passes through the windbreak transition.The current study aims to predict the flow characteristics around the existing right-angled windbreak wall,with three preliminary designs and four local improvement designs at the transition connecting the embankment and the hill cut along the high-speed railway.The detached-eddy simulation method with the realizable k-ε turbulence model was used,while the contour lines were applied to generate the realistic terrain.The velocity distributions in the existing windbreak wall transition present a fast change from the large negative value(i.e.-0.16U on windward line(WWL)and-0.20U on leeward line(LWL))to the positive value(i.e.0.47U on WWL and 0.42U on LWL)within the distance of 10h.The different locations of windbreak walls on the embankment and hill cut create a rectangular discontinuous transition.The consistency of the windproof performance is destroyed at the windbreak wall transition,resulting in a sudden gust on the railway lines.A preliminary design idea coming from the hypotenuse on a right triangle was proposed to smooth the transition from the windbreak on the cut to that on the embankment.Three included angles were discussed,and the 30ºscheme shows the best shielding performance,achieving about 46%reduction on the peak-to-peak value on the WWL and 32% on the LWL at the middle height of the train.However,the positive peaks are stil observed.On this 30ºscheme,four local improvement designs are attempted to further smooth the velocity distributions.The best design that meets three wind directions can achieve about 80% reduction of peak-to-peak values.All achievements can provide a reference for the design of windbreak walls at different transition s and improve the safety of train operation under strong winds.展开更多
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 exchang...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.展开更多
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 conc...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.展开更多
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 f...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.展开更多
基金Projects(52302447,52388102,52372369)supported by the National Natural Science Foundation of China。
文摘Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method can transform the reasonable matching problem of the porosity and windproof performance of the windbreak into a study of the relationship between the resistance coefficient of the porous medium and the aerodynamic load of the train.This study examines the influence of the hole type on the wind field behind the porosity windbreak.Then,the relationship between the resistance coefficient of the porous medium,the porosity of the windbreak,and the aerodynamic loads of the train is investigated.The results show that the porous media physical model can be used instead of the windbreak geometry to study the windbreak-train aerodynamic performance,and the process of using this method is suggested.
文摘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.
基金supported by the Forestry Industry Research Special Funds for Public Welfare Projects(201404306)the National Natural Science Foundation of China(41371034,41361001,31560235)+1 种基金the National Key Technologies R&D Program of China(2013BAC07B01)the Gansu Science Foundation for Distinguished Young Scholars(145RJDA327)
文摘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.
基金Project(2020YFA0710903)supported by the National Key R&D Program of ChinaProject(U1334205)supported by the National Natural Science Foundation of ChinaProject(1-W16W)supported by the Hong Kong Polytechnic University's Postdoc Matching Fund Scheme,China。
文摘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.
文摘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.
文摘<div style="text-align:justify;"> 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 <em>C</em><em><sub>y</sub><sup> </sup></em>and rolling moment co-efficient <em>C</em><sub><em>mx </em></sub>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. </div>
文摘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.
文摘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.
文摘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.
文摘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.
文摘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.
基金National Key Research and Development Program of China,No.2022YFF1301802The Second TibetaPlateau Scientific Expedition and Research Program,No.2019QZKK1006。
文摘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.
文摘[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).
文摘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.
基金supported by the Science and Technology Innovation Program of Hunan Province,China(Grant No.2022RC3040)the Science and Technology Research Program of China State Railway Group Co.,Ltd.(Grant No.Q2023T002)+1 种基金the Technology Research and Development Program of China Rail-way Urumqi Group Co.,Ltd.(Grant No.2023-kj-91)the Nat-ural Science Foundation of Hunan Province,China(Grant Nos.2022JJ40064 and 2022JJ30727).
文摘The embankment and the hill cut are conventional infrastructure scenarios along the railway line in windy regions.The windbreak walls with the same height are separately installed on them to guarantee the safety of train operation.However,due to the realistic terrain,the distances of windbreak walls on the embankment and hill cut from the railway centreline are not the same,generating a windbreak wall transition and causing a sudden change of the windproof performance,which contributes to the so-called'yawingphenomenon when the train passes through the windbreak transition.The current study aims to predict the flow characteristics around the existing right-angled windbreak wall,with three preliminary designs and four local improvement designs at the transition connecting the embankment and the hill cut along the high-speed railway.The detached-eddy simulation method with the realizable k-ε turbulence model was used,while the contour lines were applied to generate the realistic terrain.The velocity distributions in the existing windbreak wall transition present a fast change from the large negative value(i.e.-0.16U on windward line(WWL)and-0.20U on leeward line(LWL))to the positive value(i.e.0.47U on WWL and 0.42U on LWL)within the distance of 10h.The different locations of windbreak walls on the embankment and hill cut create a rectangular discontinuous transition.The consistency of the windproof performance is destroyed at the windbreak wall transition,resulting in a sudden gust on the railway lines.A preliminary design idea coming from the hypotenuse on a right triangle was proposed to smooth the transition from the windbreak on the cut to that on the embankment.Three included angles were discussed,and the 30ºscheme shows the best shielding performance,achieving about 46%reduction on the peak-to-peak value on the WWL and 32% on the LWL at the middle height of the train.However,the positive peaks are stil observed.On this 30ºscheme,four local improvement designs are attempted to further smooth the velocity distributions.The best design that meets three wind directions can achieve about 80% reduction of peak-to-peak values.All achievements can provide a reference for the design of windbreak walls at different transition s and improve the safety of train operation under strong winds.
基金The financial supports for this research,from the National Basic Research Program of China(Grant No.2015CB251503)Central University Fundation of China(Grant No.JB2018130)。
文摘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.
基金This work was supported by ARC Discovery Project Grant DP170104546.
文摘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.
基金supported by a grant (RIF)from the Research Grants Council of the Hong Kong Special Ad-ministrative Region (SAR),China (Grant No.R-5020-18)the National Natural Science Foundation of China (Grant No.U1934209)+1 种基金support by the Innovation and Technology Commission of the Hong Kong SAR Government (Grant No.K-BBY1)The Hong Kong Polytechnic University’s Postdoc Matching Fund Scheme (Grant No.1-W16W).
文摘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.
