Desertification is one of the most serious environmental problems in the world,especially in the arid desert regions.Combating desertification,therefore,is an urgent task on a regional or even global scale.The Taklima...Desertification is one of the most serious environmental problems in the world,especially in the arid desert regions.Combating desertification,therefore,is an urgent task on a regional or even global scale.The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the''Dead Sea''due to few organisms can exist in such a harsh environment.The Taklimakan Desert Highway,the longest desert highway(a total length of 446 km)across the mobile desert in the world,was built in the 1990s within the Taklimakan Desert.It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang,China.However,wind-blow sand seriously damages the smoothness of the desert highway and,in this case,mechanical sand control system(including sand barrier fences and straw checkerboards)was used early in the life of the desert highway to protect the road.Unfortunately,more than 70%of the sand barrier fences and straw checkerboards have lost their functions,and the desert highway has often been buried and frequently blocked since 1999.To solve this problem,a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000.However,some potential problems still exist for the sustainable development of the desert highway,such as water shortage,strong sandstorms,extreme environmental characteristics and large maintenance costs.The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway.Ultimately,we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway,such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater,screening halophytes to restore vegetation in the case of soil salinization,and planting cash crops,such as Cistanche,Wolfberry,Ap展开更多
Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of th...Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of the Golmud-Korla Railway.In this paper,wind tunnel simulation was performed on the protective effect of multiple rows of HDPE board sand fences on wind-blown sand.Two parameters have been used to reflect the protective effect of sand fences,that is,windproof efficiency and sand control efficiency,referring to the reduction rates of wind speed at a height of 0.04 m and sand flux in a run of test with the fence compared those in the control run of test without it,respectively.The test results showed that when the porosity was 30%,the single-row sand fence had the best wind proof and sand control efficiency with respective values of 46%and 65.3%.The windproof efficiencies of double-row and triple-row sand fences at 20H were 59%and 62%,respectively.Compared with the windproof effi-ciency of the single-row sand fence,those of the two-row and three-row fences increased by 13%and 16%,respectively:The maximum sand control efficiency of the double-row and triple-row sand fences were 92.1%and 96.5%,increased by 26.8%and 31.2%,respectively,compared with that of the single-row sand fence.This study indicates that the sand control efficiency after adding one or two rows was not double or triple that of the single-row fence,while the first-row sand fence played a major protective role.Compared with the double-row sand fences,the effect of the third row sand fence in triple-row sand fences is limited,and thus double-row HDPE board sand fences with the porosity of 30%are rec-ommended to control wind-blown sand along the Qinghai section of the Golmud-Korla Railway.展开更多
To control secondary flows, streamwise fences were attached to end wall of a linear turbine rotor cascade. The cascade had 8 blades of 400 mm long and 175 mm chord. The blades deflected the flow by 120°. The fenc...To control secondary flows, streamwise fences were attached to end wall of a linear turbine rotor cascade. The cascade had 8 blades of 400 mm long and 175 mm chord. The blades deflected the flow by 120°. The fences were made out of 0.7 mm thick brass sheet and the heights of the fences were 14 mm, 18 mm respectively. The curvature of the fences was the same as that of the blade camber line. The fences were fixed normal to the end wall and at half pitch away from the blades. The experimental program consists of total pressure, static pressure measurements at the inlet and outlet of the cascade, by using five-hole probe. In addition, static pressure on the blade suction surface and pressure surface was also obtained. Fences are effective in preventing the movement of the pressure side leg of the horseshoe vortex. Consequently the accumulation of low energy fluid on the suction surface is minimised. End wall losses are reduced by the fences due to weakening of the end wall cross flow.展开更多
The Golmud-Korla Railway in the Gobi area faces operational challenges due to sand hazards,caused by strong and variable winds.This study addresses these challenges by conducting wind tunnel tests to evaluate the prot...The Golmud-Korla Railway in the Gobi area faces operational challenges due to sand hazards,caused by strong and variable winds.This study addresses these challenges by conducting wind tunnel tests to evaluate the protective benefits of High Density Polyethylene(HDPE)board sand fences,focusing on their orientation relative to various wind directions(referred to as'wind angle').This study found that the size of the low-velocity zone on the leeward side of the sand fences(LSF)expanded with an increase in the wind angle(WA).At 1H(the height of the sand fence)and 2H positions on the LSF,the wind speed profiles(WSP)exhibited a segmented logarithmic growth,constrained by Z=H at varying WAs.The efficacy of the sand fence in obstructing airflow escalated as WA increased.The size of the WA has a significant impact on the protective efficiency of HDPE board sand fences.Furthermore,compared to typical sandy surfaces,the rate of sand transport across the Gobi surface diminishes more slowly with height,attributed to the gravel's rebound effect.This phenomenon allows some sand particles to bypass the fences,rendering them less effective at blocking wind and trapping sand than in sandy environments.This paper offers scientific evidence supporting the practical use and enhancement of HDPE board sand fences in varied wind conditions.展开更多
Tumbleweeds participate in a common seasonal biological process in temperate grasslands,creating hanging grass fences during the grass-withering season that result in distinct ecological phenomena.In this study,we add...Tumbleweeds participate in a common seasonal biological process in temperate grasslands,creating hanging grass fences during the grass-withering season that result in distinct ecological phenomena.In this study,we addressed the urgent need to understand and restore the degraded desert steppe in Central Mongolia,particularly considering the observed vegetation edge effects around hanging grass fences.Using field surveys conducted in 2019 and 2021 in the severely degraded desert steppe of Central Mongolia,we assessed vegetation parameters and soil physical and chemical properties influenced by hanging grass fences and identified the key environmental factors affecting vegetation changes.The results indicate that the edge effects of hanging grass fences led to changes in species distributions,resulting in significant differences in species composition between the desert steppe's interior and edge areas.Vegetation parameters and soil physical and chemical properties exhibited nonlinear responses to the edge effects of hanging grass fences,with changes in vegetation coverage,aboveground biomass,and soil sand content peaking at 26.5,16.5,and 6.5 m on the leeward side of hanging grass fences,respectively.In the absence of sand dune formation,the accumulation of soil organic carbon and available potassium were identified as crucial factors driving species composition and increasing vegetation coverage.Changes in species composition and plant density were primarily influenced by soil sand content,electrical conductivity,and sand accumulation thickness.These findings suggest that hanging grass fences have the potential to alter vegetation habitats,promote vegetation growth,and control soil erosion in the degraded desert steppe of Central Mongolia.Therefore,in the degraded desert steppe,the restoration potential of hanging grass fences during the enclosure process should be fully considered.展开更多
Concrete-plate fences have been widely adopted for windblown sand control and mitigation along railways.However,the inclination angles of inserting the concrete plate with respect to the vertical direction,i.e.,straig...Concrete-plate fences have been widely adopted for windblown sand control and mitigation along railways.However,the inclination angles of inserting the concrete plate with respect to the vertical direction,i.e.,straight or obliquely inserted concrete plates(SIP or OIP),significantly influence the efficiency of sand-control.This study performs a comparative evaluation of the SIP and OIP sand-control fences using wind tunnel testing and field monitoring data collected from the Lanzhou–Wulumuqi High-Speed Railway Project.The results show that the fence’s ability to reduce the wind speed and the sand-retaining efficiency gradually weakens with the increasing wind speed.Compared with the SIP fence,the OIP fence has a better wind speed reduction capability,stronger ability to capture fine particles below the top of the fence;it is more efficient for sand-retaining and induces stronger eddy intensity.Generally,the wind tunnel test and field monitoring results are consistent,whereas wind tunnel tests incline to overestimate wind speed reduction and sand-control efficiency.The study also finds that the aeolian sand accumulated around the fence can weaken the protection efficiency,and hence cleaning the aeolian sand accumulated around the fence should be done periodically to ensure the designed functions.展开更多
As the third play in August Wilson’s ten-play series,Fences marks a milestone for Wilson in the commercial arena and unquestionably affirms his mastery of the art of play-writing.Under the theoretical framework of Ju...As the third play in August Wilson’s ten-play series,Fences marks a milestone for Wilson in the commercial arena and unquestionably affirms his mastery of the art of play-writing.Under the theoretical framework of Julia Kristeva’s broad-sensed intertextuality,this paper explores the intertextual features of Fences to reveal that to survive in a hostile white-dominated environment where the idea of melting pot was advocated and racial discrimination remained widespread in 1950s,African Americans must discover the value of their true self.展开更多
Constructive interference between tidal stream turbines in multi-rotor fence configurations arrayed normally to the flow has been shown analytically, computationally, and experimentally to enhance turbine performance....Constructive interference between tidal stream turbines in multi-rotor fence configurations arrayed normally to the flow has been shown analytically, computationally, and experimentally to enhance turbine performance. The increased resistance to bypass flow due to the presence of neighbouring turbines allows a static pressure difference to develop in the channel and entrains a greater flow rate through the rotor swept area. Exploiting the potential improvement in turbine performance requires that turbines either be operated at higher tip speed ratios or that turbines are redesigned in order to increase thrust. Recent studies have demonstrated that multi-scale flow dynamics, in which a distinction is made between device-scale and fence-scale flow events, have an important role in the physics of flow past tidal turbine fences partially spanning larger channels. Although the reduction in flow rate through the fence as the turbine thrust level increases has been previously demonstrated, the within-fence variation in turbine performance, and the consequences for overall farm performance, is less well understood. The impact of turbine design and operating conditions, on the performance of a multi-rotor tidal fence is investigated using Reynolds-Averaged Navier-Stokes embedded blade element actuator disk simulations. Fences consisting of four, six, and eight turbines are simulated, and it is demonstrated that the combination of device-and fence-scale flow effects gives rise to cross-fence thrust and power variation. These cross-fence variations are also a function of turbine thrust, and hence design conditions,although it is shown simple turbine control strategies can be adopted in order to reduce the cross-fence variations and improve overall fence performance. As the number of turbines in the fence, and hence fence length, increases, it is shown that the turbines may be designed or operated to achieve higher thrust levels than if the turbines were not deployed in a fence configuration.展开更多
In inertial confinement fusion, the laser plasma interaction （LPI） happens when the high-energy laser irradi- ates on the target where the scattered light share generated from the stimulated Raman scattering （SRS）...In inertial confinement fusion, the laser plasma interaction （LPI） happens when the high-energy laser irradi- ates on the target where the scattered light share generated from the stimulated Raman scattering （SRS） effect is difficult to suppress. We propose a method using fence pulses （FPs） to suppress the backward SRS by inhibiting the growth of the intensity of electron plasma waves. Based on our simulation, the FPs can weaken SRS effect in the LPI effectively.展开更多
基金This work was supported by the National Natural Science Foundation of China(31971731,41771121)the Xinjiang National Key Research and Development Program(2019B00005)+1 种基金the National Key Research and Development Program(2017YFC0506705)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2017476).
文摘Desertification is one of the most serious environmental problems in the world,especially in the arid desert regions.Combating desertification,therefore,is an urgent task on a regional or even global scale.The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the''Dead Sea''due to few organisms can exist in such a harsh environment.The Taklimakan Desert Highway,the longest desert highway(a total length of 446 km)across the mobile desert in the world,was built in the 1990s within the Taklimakan Desert.It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang,China.However,wind-blow sand seriously damages the smoothness of the desert highway and,in this case,mechanical sand control system(including sand barrier fences and straw checkerboards)was used early in the life of the desert highway to protect the road.Unfortunately,more than 70%of the sand barrier fences and straw checkerboards have lost their functions,and the desert highway has often been buried and frequently blocked since 1999.To solve this problem,a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000.However,some potential problems still exist for the sustainable development of the desert highway,such as water shortage,strong sandstorms,extreme environmental characteristics and large maintenance costs.The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway.Ultimately,we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway,such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater,screening halophytes to restore vegetation in the case of soil salinization,and planting cash crops,such as Cistanche,Wolfberry,Ap
基金supported by the Young Scholars Science Foundation of Lanzhou Jiaotong University,China(2018016)the Chang Jiang Scholar and Innovation Team Development Plan of China(IRT_15R29)。
文摘Recently,sand fences,made of high density polyethylene(HDPE)board,which is resistant against harsh plateau environmental conditions,could possibly be used to control the wind-blown sand along the Qinghai section of the Golmud-Korla Railway.In this paper,wind tunnel simulation was performed on the protective effect of multiple rows of HDPE board sand fences on wind-blown sand.Two parameters have been used to reflect the protective effect of sand fences,that is,windproof efficiency and sand control efficiency,referring to the reduction rates of wind speed at a height of 0.04 m and sand flux in a run of test with the fence compared those in the control run of test without it,respectively.The test results showed that when the porosity was 30%,the single-row sand fence had the best wind proof and sand control efficiency with respective values of 46%and 65.3%.The windproof efficiencies of double-row and triple-row sand fences at 20H were 59%and 62%,respectively.Compared with the windproof effi-ciency of the single-row sand fence,those of the two-row and three-row fences increased by 13%and 16%,respectively:The maximum sand control efficiency of the double-row and triple-row sand fences were 92.1%and 96.5%,increased by 26.8%and 31.2%,respectively,compared with that of the single-row sand fence.This study indicates that the sand control efficiency after adding one or two rows was not double or triple that of the single-row fence,while the first-row sand fence played a major protective role.Compared with the double-row sand fences,the effect of the third row sand fence in triple-row sand fences is limited,and thus double-row HDPE board sand fences with the porosity of 30%are rec-ommended to control wind-blown sand along the Qinghai section of the Golmud-Korla Railway.
文摘To control secondary flows, streamwise fences were attached to end wall of a linear turbine rotor cascade. The cascade had 8 blades of 400 mm long and 175 mm chord. The blades deflected the flow by 120°. The fences were made out of 0.7 mm thick brass sheet and the heights of the fences were 14 mm, 18 mm respectively. The curvature of the fences was the same as that of the blade camber line. The fences were fixed normal to the end wall and at half pitch away from the blades. The experimental program consists of total pressure, static pressure measurements at the inlet and outlet of the cascade, by using five-hole probe. In addition, static pressure on the blade suction surface and pressure surface was also obtained. Fences are effective in preventing the movement of the pressure side leg of the horseshoe vortex. Consequently the accumulation of low energy fluid on the suction surface is minimised. End wall losses are reduced by the fences due to weakening of the end wall cross flow.
基金financially supported by the National Natural Science Foundation of China (42461011, 42071014)the Fellowship of the China Postdoctoral Science Foundation (2021M703466)
文摘The Golmud-Korla Railway in the Gobi area faces operational challenges due to sand hazards,caused by strong and variable winds.This study addresses these challenges by conducting wind tunnel tests to evaluate the protective benefits of High Density Polyethylene(HDPE)board sand fences,focusing on their orientation relative to various wind directions(referred to as'wind angle').This study found that the size of the low-velocity zone on the leeward side of the sand fences(LSF)expanded with an increase in the wind angle(WA).At 1H(the height of the sand fence)and 2H positions on the LSF,the wind speed profiles(WSP)exhibited a segmented logarithmic growth,constrained by Z=H at varying WAs.The efficacy of the sand fence in obstructing airflow escalated as WA increased.The size of the WA has a significant impact on the protective efficiency of HDPE board sand fences.Furthermore,compared to typical sandy surfaces,the rate of sand transport across the Gobi surface diminishes more slowly with height,attributed to the gravel's rebound effect.This phenomenon allows some sand particles to bypass the fences,rendering them less effective at blocking wind and trapping sand than in sandy environments.This paper offers scientific evidence supporting the practical use and enhancement of HDPE board sand fences in varied wind conditions.
基金supported by the Third Xinjiang Scientific Expedition and Research Program(2021xjkk0305)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA2003020201)the Key Intergovernmental Projects for International Scientific and Technological Innovation Cooperation of the National Key Research and Development Program of China(2017YFE0109200).
文摘Tumbleweeds participate in a common seasonal biological process in temperate grasslands,creating hanging grass fences during the grass-withering season that result in distinct ecological phenomena.In this study,we addressed the urgent need to understand and restore the degraded desert steppe in Central Mongolia,particularly considering the observed vegetation edge effects around hanging grass fences.Using field surveys conducted in 2019 and 2021 in the severely degraded desert steppe of Central Mongolia,we assessed vegetation parameters and soil physical and chemical properties influenced by hanging grass fences and identified the key environmental factors affecting vegetation changes.The results indicate that the edge effects of hanging grass fences led to changes in species distributions,resulting in significant differences in species composition between the desert steppe's interior and edge areas.Vegetation parameters and soil physical and chemical properties exhibited nonlinear responses to the edge effects of hanging grass fences,with changes in vegetation coverage,aboveground biomass,and soil sand content peaking at 26.5,16.5,and 6.5 m on the leeward side of hanging grass fences,respectively.In the absence of sand dune formation,the accumulation of soil organic carbon and available potassium were identified as crucial factors driving species composition and increasing vegetation coverage.Changes in species composition and plant density were primarily influenced by soil sand content,electrical conductivity,and sand accumulation thickness.These findings suggest that hanging grass fences have the potential to alter vegetation habitats,promote vegetation growth,and control soil erosion in the degraded desert steppe of Central Mongolia.Therefore,in the degraded desert steppe,the restoration potential of hanging grass fences during the enclosure process should be fully considered.
基金This research was supported by the Science and Technology Development Plan of China Railway Group Limited(Grant No.2015-kj035-g004-03).
文摘Concrete-plate fences have been widely adopted for windblown sand control and mitigation along railways.However,the inclination angles of inserting the concrete plate with respect to the vertical direction,i.e.,straight or obliquely inserted concrete plates(SIP or OIP),significantly influence the efficiency of sand-control.This study performs a comparative evaluation of the SIP and OIP sand-control fences using wind tunnel testing and field monitoring data collected from the Lanzhou–Wulumuqi High-Speed Railway Project.The results show that the fence’s ability to reduce the wind speed and the sand-retaining efficiency gradually weakens with the increasing wind speed.Compared with the SIP fence,the OIP fence has a better wind speed reduction capability,stronger ability to capture fine particles below the top of the fence;it is more efficient for sand-retaining and induces stronger eddy intensity.Generally,the wind tunnel test and field monitoring results are consistent,whereas wind tunnel tests incline to overestimate wind speed reduction and sand-control efficiency.The study also finds that the aeolian sand accumulated around the fence can weaken the protection efficiency,and hence cleaning the aeolian sand accumulated around the fence should be done periodically to ensure the designed functions.
文摘As the third play in August Wilson’s ten-play series,Fences marks a milestone for Wilson in the commercial arena and unquestionably affirms his mastery of the art of play-writing.Under the theoretical framework of Julia Kristeva’s broad-sensed intertextuality,this paper explores the intertextual features of Fences to reveal that to survive in a hostile white-dominated environment where the idea of melting pot was advocated and racial discrimination remained widespread in 1950s,African Americans must discover the value of their true self.
文摘Constructive interference between tidal stream turbines in multi-rotor fence configurations arrayed normally to the flow has been shown analytically, computationally, and experimentally to enhance turbine performance. The increased resistance to bypass flow due to the presence of neighbouring turbines allows a static pressure difference to develop in the channel and entrains a greater flow rate through the rotor swept area. Exploiting the potential improvement in turbine performance requires that turbines either be operated at higher tip speed ratios or that turbines are redesigned in order to increase thrust. Recent studies have demonstrated that multi-scale flow dynamics, in which a distinction is made between device-scale and fence-scale flow events, have an important role in the physics of flow past tidal turbine fences partially spanning larger channels. Although the reduction in flow rate through the fence as the turbine thrust level increases has been previously demonstrated, the within-fence variation in turbine performance, and the consequences for overall farm performance, is less well understood. The impact of turbine design and operating conditions, on the performance of a multi-rotor tidal fence is investigated using Reynolds-Averaged Navier-Stokes embedded blade element actuator disk simulations. Fences consisting of four, six, and eight turbines are simulated, and it is demonstrated that the combination of device-and fence-scale flow effects gives rise to cross-fence thrust and power variation. These cross-fence variations are also a function of turbine thrust, and hence design conditions,although it is shown simple turbine control strategies can be adopted in order to reduce the cross-fence variations and improve overall fence performance. As the number of turbines in the fence, and hence fence length, increases, it is shown that the turbines may be designed or operated to achieve higher thrust levels than if the turbines were not deployed in a fence configuration.
文摘In inertial confinement fusion, the laser plasma interaction （LPI） happens when the high-energy laser irradi- ates on the target where the scattered light share generated from the stimulated Raman scattering （SRS） effect is difficult to suppress. We propose a method using fence pulses （FPs） to suppress the backward SRS by inhibiting the growth of the intensity of electron plasma waves. Based on our simulation, the FPs can weaken SRS effect in the LPI effectively.
