基于表层岩土渗透对三峡井网井水位降雨影响的精准分析          下载免费PDF全文

周洋  吴艳霞  罗棋  李查玮 《地震工程学报》2020,42(2):460-467,528

为研究三峡井网表层岩土渗透对井水位降雨的影响,采取井区表层岩土垂向渗透性测试方法试验,测得表层岩土垂向渗透性,并建立数学模型,用于降雨渗入补给分析。在此模型基础上,通过三峡井网8口井水位、气象三要素的对比观测资料对井水位日动态、月动态、年动态的影响进行精准分析与验证。结果表明:这种影响的特征是相当复杂的,同一个降雨过程在不同井上产生的影响特征不同,这一方面可能与各井的水文地质条件不同有关,另一方面可能还与各井点的降雨过程的差异也有关。  相似文献   

Quantifying flow resistance in mountain streams using computational fluid dynamics modeling over structure-from-motion photogrammetry-derived microtopography     

Yunxiang Chen  Roman A. DiBiase  Nicholas McCarroll  Xiaofeng Liu 《地球表面变化过程与地形》2019,44(10):1973-1987

Flow resistance in mountain streams is important for assessing flooding hazard and quantifying sediment transport and bedrock incision in upland landscapes. In such settings, flow resistance is sensitive to grain-scale roughness, which has traditionally been characterized by particle size distributions derived from laborious point counts of streambed sediment. Developing a general framework for rapid quantification of resistance in mountain streams is still a challenge. Here we present a semi-automated workflow that combines millimeter- to centimeter-scale structure-from-motion (SfM) photogrammetry surveys of bed topography and computational fluid dynamics (CFD) simulations to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. The workflow was applied to three field sites of gravel, cobble, and boulder-bedded channels with a wide range of grain size, sorting, and shape. Large-eddy simulations with body-fitted meshes generated from SfM photogrammetry-derived surfaces were performed to quantify flow resistance. The analysis of bed microtopography using a second-order structure function identified three scaling regimes that corresponded to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation σ_z of detrended streambed elevation normalized by water depth, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance and is furthermore tied to the characteristic length scale of rough surface-generated vortices. Horizontal length scales and surface complexity are secondary controls on flow resistance. A new resistance predictor linking water depth and vertical roughness scale, i.e.  H/σ_z, is proposed based on the comparison between σ_z and the characteristic length scale of vortex shedding. In addition, representing streambeds using digital elevation models (DEM) is appropriate for well-sorted streambeds, but not for poorly sorted ones under shallow and medium flow depth conditions due to the missing local overhanging features captured by fully 3D meshes which modulate local pressure gradient and thus bulk flow separation and pressure distribution. An appraisal of the mesh resolution effect on flow resistance shows that the SfM photogrammetry data resolution and the optimal CFD mesh size should be about 1/7 to 1/14 of the standard deviation of bed elevation. © 2019 John Wiley & Sons, Ltd.  相似文献   

Dynamics and driving mechanisms of asymmetric human water consumption during alternating wet and dry periods   总被引：1，自引：1，他引：0  

Fuqiang Tian  You Lu  Hongchang Hu  Wolfgang Kinzelbach  Murugesu Sivapalan 《水文科学杂志》2019,64(5):507-524

Increases in human water consumption (HWC) and consequent degradation of the ecological environment are common in arid regions. Understanding the mechanisms behind these processes is important for sustainable development. Analyses of changes in HWC between alternating wet and dry periods are carried out in four arid inland basins in Central Asia and China (Syr Darya, Tarim, Heihe and Shulehe river basins). Based on runoff records, the presence of an asymmetric HWC response is proved (p < 0.01), with an increase in HWC during wet periods and a muted decrease during subsequent dry periods. This behaviour is interpreted by invoking theories from behavioural economics at the individual and community levels. A simple model based on these theories is shown to be able to reproduce the observed dynamics and is used to discuss the importance of strengthening institutional factors for water sustainability.  相似文献   

On stellar encounters and their effect on cometary orbits in the Oort cloud     

R.A. Serafin  H.‐G. Grothues 《Astronomische Nachrichten》2002,323(1):37-48

We systematically investigate the encounters between the Sun and neighbouring stars and their effects on cometary orbits in the Oort cloud, including the intrinsic one with the star Gl 710 (HIP 89 825), with some implications to stellar and cometary dynamics. Our approach is principally based on the combination of a Keplerian‐rectilinear model of stellar passages and the Hipparcos Catalogue (ESA 1997). Beyond the parameters of encounter, we pay particular attention to the observational errors in parallaxes and stellar velocities, and their propagation in time. Moreover, as a special case of this problem, we consider the collision probability of a star passing very closely to the Sun, taking also into account the mutual gravitational attraction between the stars. In the part dealing with the influence of stellar encounters on the orbital elements of Oort cloud comets, we derive new simple formulae calculating the changes in the cometary orbital elements, expressed as functions of the Jeans impulse formula. These expressions are then applied to calculate numerical values of the element changes caused by close encounters of neighbouring stars with some model comets in the Oort cloud. Moreover, the general condition for an ejection of comets from the cloud effected by a single encounter is derived and discussed.  相似文献   

Aquatic vegetation dynamics in two pit lakes related to interannual water level fluctuation     

Lilin Zheng  Pengfei Zhan  Jinying Xu  Ligang Xu  Zhiqiang Tan  Xiaolong Wang 《水文研究》2020,34(11):2645-2659

Water regime characteristics have been recognized as critical factors for aquatic vegetation. In this study, we examined changes in aquatic vegetation coverage area in two shallow sub-lakes of Poyang Lake (Bang Lake and Cuoji Lake) during the dry season from 1987 to 2017. The relationships between eight water regime components (annual average water level, annual maximum water level, annual minimum water level, and flooded days at five water levels [11, 13, 15, 17, and 19 m]) and aquatic vegetation coverage area were determined. The most critical water regimes were identified and results demonstrated that aquatic vegetation coverage area in Bang Lake and Cuoji Lake peaked in drier years (2005 and 2009, respectively) with no obvious up or down trend. Water regimes indicating high flow events such as annual maximum water level, flooded days at water level 19 m, and annual average water level were found to be more important for predicting aquatic vegetation. High-flow events appear to be essential for understanding aquatic vegetation dynamics in pit lakes, yet overall the influences of water level fluctuation on aquatic vegetation varied among wetland units of Poyang Lake. This study helps to understand the hydroecological dynamics in connected lakes further and provide a reference for the lake management and protection.  相似文献   

中国省域二氧化碳排放的时空格局及影响因素     

王瑛  何艳芬 《世界地理研究》2020,29(3):512-522

通过测算全国30个省域2000—2015年的二氧化碳排放量，采用自然段点法，分别对2000年、2005年、2010年和2015年各省碳排放量进行分类，分析其空间分异化特征。采用空间自相关分析法揭示了相邻各省份碳排放量的空间关联性。在此基础上，运用对数均值迪氏分解法，从能源结构、能源强度、经济发展和人口规模等角度，对碳排放影响因素进行无残差分解。结果表明：1）时间上，我国碳排放总量整体呈上升趋势，在2014—2015年仅下降2%。除北京市外，其余各省份的碳排放量呈增长趋势；空间上，高值碳排放由环渤海及东部沿海省份逐步蔓延至中西部个别省份;2）各省域碳排放主要呈现高高集聚和低高集聚的特征，高高集聚稳定集中在辽宁、河北、山东、山西和江苏省，北京市和天津市与高碳排放的省份形成一个低高集聚区域;3）东、中部比西部省份更易受能源结构、能源强度、经济发展和人口规模等因素的影响。经济发展对碳排放是驱动作用，能源强度对碳排放是抑制作用，能源结构对各省份碳排放的影响有正向驱动和负向抑制作用，除贵州省外，其余省份人口规模对碳排放均是正向驱动作用。  相似文献   

Mining spatiotemporal association patterns from complex geographic phenomena     

Zhanjun He  Jiannan Cai  Zhong Xie  Qingfeng Guan  Chao Yang 《International journal of geographical information science》2020,34(6):1162-1187

ABSTRACT

Spatiotemporal association pattern mining can discover interesting interdependent relationships among various types of geospatial data. However, existing mining methods for spatiotemporal association patterns usually model geographic phenomena as simple spatiotemporal point events. Therefore, they cannot be applied to complex geographic phenomena, which continuously change their properties, shapes or locations, such as storms and air pollution. The most salient feature of such complex geographic phenomena is the geographic dynamic. To fully reveal dynamic characteristics of complex geographic phenomena and discover their associated factors, this research proposes a novel complex event-based spatiotemporal association pattern mining framework. First, a complex geographic event was hierarchically modeled and represented by a new data structure named directed spatiotemporal routes. Then, sequence mining technique was applied to discover the spatiotemporal spread pattern of the complex geographic events. An adaptive spatiotemporal episode pattern mining algorithm was proposed to discover the candidate driving factors for the occurrence of complex geographic events. Finally, the proposed approach was evaluated by analyzing the air pollution in the region of Beijing-Tianjin-Hebei. The experimental results showed that the proposed approach can well address the geographic dynamic of complex geographic phenomena, such as the spatial spreading pattern and spatiotemporal interaction with candidate driving factors.  相似文献   

沉管隧道卵石与碎石垫层力学变形特性对比研究     

王勇  穆清君  过超  付佰勇  何潇 《岩土力学》2020,41(10):3425-3431

国内外沉管隧道先铺基础多采用碎石作为垫层材料，目前尚无采用卵石的先例。卵石和碎石在表面光滑度、排列接触方式、颗粒间天然空隙率等物理特性的差异性将影响其力学性能表现。通过物理模型试验和数值模拟计算，对卵石和碎石垫层的力学变形特性进行对比分析。研究表明：（1）两种材料垫层压缩曲线均呈两阶段反弯曲线变化趋势，相同荷载条件下卵石垫层压缩量较碎石高，总体割线模量较碎石低约30%。（2）垫层厚度由0.8 m变为1 m时，卵石垫层割线模量增加了13.0%，碎石垫层割线模量增加了2.2%；卵石垫层力学变形性能对垫层厚度的变化较碎石垫层更敏感。（3）预压荷载由52.5 kPa增加到84 kPa时，卵石垫层割线模量增加了23.5%，碎石垫层割线模量增加了7.6%；预压荷载越大，卵石垫层能更早达到拐点从而表现出更稳定的力学性能；增加预压荷载对卵石垫层整体力学变形性能的改善较碎石垫层更明显。（4）随沟宽增大，垫层模量在前期再压缩阶段出现模量提高，而在全加载期内总体表现为模量降低；在全荷载范围内卵石垫层对垄沟尺寸变化的敏感度低于碎石垫层。（5）碎石垫层的整体力学性能优于卵石垫层，但两种垫层材料对结构沉降和受力状态的影响相对有限；在对施工偏差敏感度充分分析的基础上，卵石可替代碎石作为沉管隧道垫层材料。（6）开展卵石级配试验研究，获取最佳卵石级配，是未来研究方向。  相似文献   

青岛灵山岛南背来石下白垩统大型砂脉的发现及其形成动力学研究     

钟建华  倪良田  汪立东  宋全友  孙宁亮  宋冠先  薛纯琦  郝兵  邵珠福  毛毳  刘闯  曹梦春 《地质论评》2020,66(6):1457-1475

青岛灵山岛南背来石剖面发育了两层大型不规则砂脉。其主要特征如下：上层大型不规则砂脉呈分散团块状顺黄褐色凝灰质泥岩分布，断续延伸约60 m，宽数米；有17个侵入砂团块。砂团块多呈浅灰色，主要岩性为砂岩、砂砾岩；砂团块直径在1~2 m。砂团块的形态非常复杂，侧向极易尖灭或突然中止。边界与围岩多突变，某些地方与节理发育方向相同。下层大型不规则砂脉浅灰色，主要底部为砂岩、顶部为砂砾岩，呈透镜状顺层产于灰黑色薄层砂泥岩中，均一团块状和边缘含大量泥砾；厚18 m，宽度和高度不详；上层砂脉发育在浅湖中；下层大型不规则砂脉发育在三角洲前缘。与此同时还探讨了上层砂脉的形成的动力学机制，建立了顺层砂脉的形成深度与液化层的深度之间的关系式（h=0.29H）。该公式可以用来预测顺层的侵位深度和寻找砂脉，为含油气盆地砂脉储层预测提供理论依据和新方法。通过流化公式计算获得了形成上层砂脉的流体上侵速度为1.26 m/s。通过本文的论述，进一步为理解灵山岛地区下白垩统的沉积环境和沉积动力学特征提供了新的岩石学证据。  相似文献   

地震预报的科学哲学与方法论探索——50年回眸与前瞻     

周硕愚  江在森  申重阳  吴云  张燕 《大地测量与地球动力学》2019,39(7):661-676

地震预报是具高度复杂性的世界科学难题。以我国50余年实践中的问题为导向，以其揭示的自然现象为依托，从科学哲学及方法论视角，回顾经验归纳、还原论动力学、归纳-演绎和复杂动力系统等方法。通过汶川、唐山等震例探讨认识论因素在预测预报中的重要作用。进入地球系统科学新时期，建议以大陆变形复杂动力系统演化及其地震行为、经验与数值预测桥梁的图像（斑图）动力学作为地震预报的自然观和方法论。它们虽不完善，但更贴近大自然的整体性、进化性和非线性本质，又能包容连接多种思路与方法；既具前瞻性，又具可操作性；地震具可预测性，又具预测的不完全确定性；预测→预报→减轻灾害尚存在颇大的可创新空间。  相似文献