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981.
祁连山夏季地形云综合探测试验 总被引:1,自引:0,他引:1
2006年和2007年夏季在祁连山冷龙岭西段开展了地形云云量、云状、大气水汽、风场、雨滴谱和雨强等的综合探测试验,以分析祁连山地形云的特征。结果表明:①祁连山区夏季云量丰富,平均云量在6成以上。西南气流天气背景下总云量多达8成;②祁连山夏季无降水日大气水汽非常少,700 hPa以上层大气相对湿度大多在20%以下;③西南气流背景下祁连山南北侧山谷风的共同作用,气流昼间向山顶辐合,夜间向山谷辐散,当水汽条件充足时,极易抬升形成可以产生降水的地形云;④祁连山降水主要由小于1 mm的雨滴组成。 相似文献
982.
作为非开挖施工的一个分支,定向钻穿越技术得到了越来越广泛的应用。本文以DN630供水管道定向钻穿越淮河工程为例,介绍了定向钻穿越的技术特点,指出了设计基本原则及设计要素如管道钻进的入土角、出土角、曲率半径和穿越深度等确定方法,并阐述了定向钻穿越施工工艺流程及泥浆配制、钻导向孔、扩孔及管道回拖等主要施工工艺。 相似文献
983.
Numerical Investigation of the Dynamic Mechanical State of a Coal Pillar During Longwall Mining Panel Extraction 总被引:2,自引:1,他引:1
Hongwei Wang Yaodong Jiang Yixin Zhao Jie Zhu Shuai Liu 《Rock Mechanics and Rock Engineering》2013,46(5):1211-1221
This study presents a numerical investigation on the dynamic mechanical state of a coal pillar and the assessment of the coal bump risk during extraction using the longwall mining method. The present research indicates that there is an intact core, even when the peak pillar strength has been exceeded under uniaxial compression. This central portion of the coal pillar plays a significant role in its loading capacity. In this study, the intact core of the coal pillar is defined as an elastic core. Based on the geological conditions of a typical longwall panel from the Tangshan coal mine in the City of Tangshan, China, a numerical fast Lagrangian analysis of continua in three dimensions (FLAC3D) model was created to understand the relationship between the volume of the elastic core in a coal pillar and the vertical stress, which is considered to be an important precursor to the development of a coal bump. The numerical results suggest that, the wider the coal pillar, the greater the volume of the elastic core. Therefore, a coal pillar with large width may form a large elastic core as the panel is mined, and the vertical stress is expected to be greater in magnitude. Because of the high stresses and the associated stored elastic energy, the risk of coal bumps in a coal pillar with large width is greater than for a coal pillar with small width. The results of the model also predict that the peak abutment stress occurs near the intersection between the mining face and the roadways at a distance of 7.5 m from the mining face. It is revealed that the bump-prone zones around the longwall panel are within 7–10 m ahead of the mining face and near the edge of the roadway during panel extraction. 相似文献
984.
Impact of Gas Adsorption Induced Coal Matrix Damage on the Evolution of Coal Permeability 总被引:1,自引:1,他引:0
W. C. Zhu C. H. Wei J. Liu T. Xu D. Elsworth 《Rock Mechanics and Rock Engineering》2013,46(6):1353-1366
It has been widely reported that coal permeability can change from reduction to enhancement due to gas adsorption even under the constant effective stress condition, which is apparently inconsistent with the classic theoretical solutions. This study addresses this inconsistency through explicit simulations of the dynamic interactions between coal matrix swelling/shrinking induced damage and fracture aperture alteration, and translations of these interactions to permeability evolution under the constant effective stress condition. We develop a coupled coal–gas interaction model that incorporates the material heterogeneity and damage evolution of coal, which allows us to couple the progressive development of damage zone with gas adsorption processes within the coal matrix. For the case of constant effective stress, coal permeability changes from reduction to enhancement while the damage zone within the coal matrix develops from the fracture wall to further inside the matrix. As the peak Langmuir strain is approached, the decrease of permeability halts and permeability increases with pressure. The transition of permeability reduction to permeability enhancement during gas adsorption, which may be closely related to the damage zone development in coal matrix, is controlled by coal heterogeneity, external boundary condition, and adsorption-induced swelling. 相似文献
985.
扬子地块古生代大地构造演化及古地磁学研究综述 总被引:5,自引:0,他引:5
本文简要地论述了扬子地块古生代大地构造研究现状,扬子与华夏地块之间的华南裂谷盆地于奥陶纪初发生收缩,直到加里东末期基本封闭,古生代扬子地块与华北地块之间的秦岭海槽以拉张为主,扬子地块西缘古生代期间处于相对稳定的构造环境,古生代末进入特提斯构造域,发生活化。 相似文献
986.
987.
城市化进程加快导致街道安全性问题突出,已有研究利用城市视觉要素刻画街道安全感空间分布,忽略了街道真实安全性与安全感间的差异。该文利用街景影像和手机信令数据,结合K-means聚类算法与笛卡尔积运算模型减少“安全感知差异”,以长沙市主城区为研究案例,得到白天、夜晚及总体城市街道安全性分布:1)长沙市主城区安全感指数随圈层数增加呈波动递减趋势,主要原因是建筑视觉要素占比下降较快以及天空视觉要素占比逐步上升;2)长沙市主城区呈双圈层结构,白天高安全性、夜晚低安全性以及总体安全性最低的区域主要分布在主城区中心,具有明显的聚集现象。该研究通过对城市街道安全性和低安全性街道的分析提出街道优化建议,为城市规划提供参考。 相似文献
988.
It is widely believed that the evolution of solar active regions leads to solar flares. However, information about the evolution of solar active regions is not employed in most existing solar flare forecasting models. In the current work, a shortterm solar flare forecasting model is proposed, in which sequential sunspot data, including three days of information about evolution from active regions, are taken as one of the basic predictors. The sunspot area, the McIntosh classification, the magnetic classification and the radio flux are extracted and converted to a numerical format that is suitable for the current forecasting model. Based on these parameters, the sliding-window method is used to form the sequential data by adding three days of information about evolution. Then, multi-layer perceptron and learning vector quantization are employed to predict the flare level within 48 h. Experimental results indicate that the performance of the proposed flare forecasting model works better than previous models. 相似文献
989.
We develop a method based on the samples from Apollo and Luna landing sites to determine lunar TiO2 content with Chang’E-1 interference imaging spectrometer (IIM) imagery. By analyzing the nonlinear relationship between the optical and compositional parameters of lunar soil samples, the method employs two Support Vector Machines (SVMs) to estimate the titanium abundance of the lunar surface. Developed with the soil compositions of the Apollo and Luna sample-return stations, the RMS (root mean square) error of our method is 0.24 wt% TiO2, and the correlation coefficient of the TiO2 values and our predicted ones is 99.72 %. Compared with the other 3 models, the method proposed in this paper exhibits a good performance for determining the chemical composition of the lunar surface. TiO2 maps of Sinus Iridum, part of the Marius Hills plateau, and part of Mare Smythii are produced using our method, which could be useful for future lunar missions. 相似文献
990.
The diffusion mechanism of charged particles is one of the very im- portant problems in astrophysics. Recently, Matthaeus et al. (2003) developed a nonlinear guiding center theory (NLGC) of the perpendicular diffusion of en- ergetic charged particles with the parallel diffusion coefficient as an input. This theory agrees with the results of numerical simulations very well. In addition, Qin (2007) developed a nonlinear parallel diffusion theory (NLPA) following the idea of NLGC. Combining the NLGC with the NLPA, a new theory, NLGC-E was developed to solve the parallel and perpendicular diffusion coefficients simultaneously. In the NLGC theory, there is a coefficient a2 which is selected to be 1/3 for the best agreement with the results of numerical simulations. In this work we tried the different values of a2 for the NLGC-E theory to determine the optimal value which ?ts best the results of numerical simulations. 相似文献