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11.
宽浅陡槽水流试验研究表明,浅层急流的阻力大、稳定性差。当陡槽(B/h<40,hk>1.04 m)末端水流呈"马鞍型"动量横向分布时,水流具有较强的稳定性;而当陡槽(B/h>40,hk<1.04 m)末端水流呈"椭圆型"动量横向分布时,就缺乏抗干扰能力,导致下游形成平面涡旋并挤压水跃。基于"介入式"方法,提出了采用潜没式三角翼体来调控浅层急流。利用三角翼对两翼底层水流产生的扰动产生两翼优势流,从而使水体能够抑制边界微小扰动的"多米诺骨牌"累加递增效应,提高了水流整体稳定性,改善了下游水流的衔接消能,效果良好。在此基础上,对三角翼体调控水流动量分布的机理进行了分析,探讨了三角翼体型设计原则及量纲一体型因子k的确定方法。 相似文献
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The formation of landslide dams is often induced by earthquakes in mountainous areas.The failure of a landslide dam typically results in catastrophic flash floods or debris flows downstream.Significant attention has been given to the processes and mechanisms involved in the failure of individual landslide dams.However,the processes leading to domino failures of multiple landslide dams remain unclear.In this study,experimental tests were carried out to investigate the domino failure of landslide dams and the consequent enlargement of downstream debris flows.Different blockage conditions were considered,including complete blockage,partial blockage and erodible bed(no blockage).The mean velocity of the flow front was estimated by videos.Total stress transducers(TSTs)and Laser range finders(LRFs) were employed to measure the total stress and the depth of the flow front,respectively.Under a complete blockage pattern,a portion of the debris flow was trapped in front of each retained landslide dam before the latter collapsed completely.This was accompanied by a dramatic decrease in the mean velocity of the flow front.Conversely,under both partial blockage and erodible bed conditions,the mean velocity of the flow front increased gradually downward along the sloping channel.Domino failures of the landslide dams were triggered when a series of dams(complete blockage and partial blockage) were distributed along the flume.However,not all of these domino failures led to enlarged debris flows.The modes of dam failures have significant impacts on the enlargement of debris flows.Therefore,further research is necessary to understand the mechanisms of domino failures of landslide dams and their effects on the enlargement of debris flows. 相似文献
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我国坡地资源利用生态环境效应的研究现状综述 总被引:3,自引:0,他引:3
坡地资源是重要的土地资源,开发利用坡地资源是人类极为重要的物资来源。坡地资源利用存在正负两方面的生态环境效应,合理利用有利于养分和水分的循环,不适宜的开发利用将导致养分和水分循环的失调,坡地资源退化。因此,开展坡地资源利用及其生态环境效应研究,探讨各地开发、利用坡地资源模式及坡地资源退化防治措施,对农业生产实践具有十分重要的理论指导意义。文中从3个方面介绍我国坡地资源利用生态环境效应的研究现状:一是坡地资源利用研究的理论方法,包括实地观测试验与防治措施研究;二是从不同尺度包括区域尺度、小流域尺度和坡面尺度研究坡地资源利用的生态环境问题;三是研究坡地资源利用的生态环境效应。最后,综合分析我国坡地资源利用生态环境效应研究存在的问题,指出今后展开深入研究的方向。 相似文献
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《生态环境状况评价技术规范(试行)》中若干值得商榷的问题 总被引:2,自引:0,他引:2
分析了<生态环境状况评价技术规范(试行)>(简称<规范>)中指标使用、计算方法和应用范围等值得商榷的问题.认为<规范>中的湿地除了应包括天然湿地外还应包含人工湿地,同时应将湿地作为水网的重要构成;未利用地中的部分指标在国家尺度上不具有代表性:将各类水网指标直接相加而不进行权重分配有失客观;归一化方法使用上没有统一.<规范>对于同一区域生态环境状况的动态变化评价没有意义,且不适用于城市内设区的区级行政单位生态环境状况评价.建议根据各区域生态环境特征建立分区的评价指标体系,指标应具有很强的代表性、可比性和操作性,在指数计算中应对各指数及其下设指标分别进行权重分配,各指数均应进行归一化,同一区域不同时期各指标的归一化系数应保持恒定. 相似文献
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简述了Lotus公司推出的办公自动化网络平台应用软件Domino/Notes R5.0.1.使大家更好地了解服务器的分类、配置及客户机基本配置.结合具体情况,详细介绍了层次结构命名系统、邮件文件的数据流向以及办公自动化系统网络的物理结构. 相似文献
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In this paper, temporal dynamics of eco-environmental changes in coastal areas of China during 1981–2000 are investigated
based on four key surface parameters including normalized difference vegetation index (NDVI), thermal index, moisture index
and surface broadband albedo derived from quantitative remote sensing techniques and meteorological data. Firstly, land surface
temperature (LST) and land surface broadband albedo are retrieved by the split-window algorithms and high-order polynomial
regression method, respectively, using NOAA/AVHRR series images. Then, moisture index and thermal index, indicators of climate
and moisture conditions in the study area, are computed from meteorological data and LST using principal component analysis
(PCA). Finally, long-term dynamics of these eco-environmental factors and the reasons responsible for these changes are analyzed
further. The results show that during the years from 1981 to 2000, the study area experienced a gradual increase in annual
NDVI and climate factors and a decrease in surface annual broadband albedo, which indicates that the coastal thermal and moisture
conditions and the subsistence conditions of natural vegetation have changed to a considerable extent. According to the results,
a warming and wetting tendency over the last two decades is obvious in the China’s coastal zone that are mainly due to land
use changes as of growing urbanization, exhaust emissions from industries and transportations and, partly global climate change.
Uncontrolled rapid development of the study area may be blamed for these negative changes as a major driving force. The positive
feedback mechanisms between albedo, NDVI and climate factors also partly explain these changes. This study suggests that the
method integrating biophysical parameters retrieved from remote sensed images and meteorologic data provides a novel and feasible
way to monitor large scale eco-environmental changes.
相似文献
Q. QinEmail: |
20.
Eco-environmental effects of the Qinghai-Tibet Plateau uplift during the Quaternary in China 总被引:4,自引:0,他引:4
The Qinghai–Tibet Plateau uplifted >3000 m in the Quaternary period. The average rate of uplift was 1–1.1 mm/year. The uplifting
has remolded the geomorphology of China. The landform in China was changed from west-low and east-high to west-high and east-low
in three steps. The Qinghai-Tibet Plateau uplift is an important factor that affected the climate and the environment of China
in the Quaternary period. It controls atmospheric circulation and climatic change in Asia and even the northern hemisphere,
by dividing the westerlies into two branches: south and north. The plateau gradually became a heat source in summer and a
cold source in winter. The uplift had a decisive effect on the formation of the East-Asia monsoon, which increased the climatic
differences between the glacial period and the interglacial period. The climate and environment of China are characterized
by the influences of the plateau uplift. The east of China became the south-east monsoon area, whereas the south-west became
the south-west monsoon area and the north-west turned into an arid inland region. The Gobi and large-scale deserts that formed
in the inland basins are ceaselessly extending. The climate of northern China became more arid as the Qinghai-Tibet Plateau
continued to uplift. The Plateau uplift affected glacial evolvement and loess formation, and propelled the migration of cold-
and warm-blooded animals, which differed from other regions of the world at the same latitude.
Received: 30 August 1999 · Accepted: 18 April 2000 相似文献