Taibus County, Inner Mongolia, China, lies in a farming-pastoral ecotone, where severe wind erosion and various aeolian sand hazards are prevalent and fixed and semi-fixed sand dunes occur frequently. This study was c...Taibus County, Inner Mongolia, China, lies in a farming-pastoral ecotone, where severe wind erosion and various aeolian sand hazards are prevalent and fixed and semi-fixed sand dunes occur frequently. This study was conducted to investigate the relationships between sand transportation rate and wind speed for the fixed and semi-fixed sand dunes based on field measurements. The annual quantity of soil erosion by wind was estimated using meteorological wind data. The results indicated that the sand transportation rate in Taibus County in 2000 was 57.38 kg cm-1 year-1 for the semi-fixed dunes and 4.56 kg cm-1 year-1 for the fixed dunes. The total duration of erosive winds covered 12.5% of the time of the year, and spring posed the highest potential of sand transportation. Wind with low speed (≤ 17 m s-1) and high frequency plays a dominant role in sand transportation, while strong wind (≥ 17 m s-1) with low frequency significantly enhanced the sand transportation. Erosive wind speed, directions, and frequency were three crucial dynamic factors influencing sand hazards in the farming-pastoral ecotone. The dominant factors intensifying sand and dust storms in Taibus County might be related to the favorable wind condition in combination with the durable drought, which led to land desertification and vegetation degradation.展开更多
A laboratory study was conducted using particle image velocimetry(PIV)to measure flow velocity distributions over two-dimensional smooth and rough fixed dunes.It comprised 28 tests,each yielding 146 velocity profiles ...A laboratory study was conducted using particle image velocimetry(PIV)to measure flow velocity distributions over two-dimensional smooth and rough fixed dunes.It comprised 28 tests,each yielding 146 velocity profiles over one complete dune length.Two kinds of double-averaged velocity profiles were computed,one based on all the 146 lines of data(called global average),and the others from only some of them(called partial average).The results show that the global average velocity distribution is generally close to the partial average profile derived from evenly-distributed three or five lines along one dune length.Furthermore,the global average velocity profile can also be reasonably approximated using a single profile,measured at the representative line in this paper.The representative line is found to locate near the reattachment point.This result would be helpful to simplify measurements of general velocity distribution for a flow over dunes.The paper also applies the concept of representative line to the description of distributioAverage velocity profile turbulent flows fixed dunes representative linens of turbulence characteristics.展开更多
基金supported by the National Natural Science Foundation of China (No.40771021)the Ministry of Education ofChina (No.20070027020)the Ministry of Science & Technology of China (Nos.2006BAD20B03 and 2006BAD20B02).
文摘Taibus County, Inner Mongolia, China, lies in a farming-pastoral ecotone, where severe wind erosion and various aeolian sand hazards are prevalent and fixed and semi-fixed sand dunes occur frequently. This study was conducted to investigate the relationships between sand transportation rate and wind speed for the fixed and semi-fixed sand dunes based on field measurements. The annual quantity of soil erosion by wind was estimated using meteorological wind data. The results indicated that the sand transportation rate in Taibus County in 2000 was 57.38 kg cm-1 year-1 for the semi-fixed dunes and 4.56 kg cm-1 year-1 for the fixed dunes. The total duration of erosive winds covered 12.5% of the time of the year, and spring posed the highest potential of sand transportation. Wind with low speed (≤ 17 m s-1) and high frequency plays a dominant role in sand transportation, while strong wind (≥ 17 m s-1) with low frequency significantly enhanced the sand transportation. Erosive wind speed, directions, and frequency were three crucial dynamic factors influencing sand hazards in the farming-pastoral ecotone. The dominant factors intensifying sand and dust storms in Taibus County might be related to the favorable wind condition in combination with the durable drought, which led to land desertification and vegetation degradation.
基金supported by the National Natural Science Foundation of China(Grant No.51979242).
文摘A laboratory study was conducted using particle image velocimetry(PIV)to measure flow velocity distributions over two-dimensional smooth and rough fixed dunes.It comprised 28 tests,each yielding 146 velocity profiles over one complete dune length.Two kinds of double-averaged velocity profiles were computed,one based on all the 146 lines of data(called global average),and the others from only some of them(called partial average).The results show that the global average velocity distribution is generally close to the partial average profile derived from evenly-distributed three or five lines along one dune length.Furthermore,the global average velocity profile can also be reasonably approximated using a single profile,measured at the representative line in this paper.The representative line is found to locate near the reattachment point.This result would be helpful to simplify measurements of general velocity distribution for a flow over dunes.The paper also applies the concept of representative line to the description of distributioAverage velocity profile turbulent flows fixed dunes representative linens of turbulence characteristics.
