强降雨下基于Green-Ampt模型的边坡稳定性分析     

苏永华  李诚诚 《岩土力学》2020,41(2):389-398

降雨入渗分析方法直接影响降雨型滑坡的预测与防范。Green-Ampt（GA）模型物理意义明确、参数较少，在降雨型滑坡分析中逐渐得到了重视，但该方法忽略了湿润层非饱和层的存在以及饱和层渗流而影响计算精度。针对以上不足，基于GA模型，建立了适用于边坡并且能综合考虑湿润层土体含水率分布情况与饱和层内平行于坡面渗流作用的降雨入渗分析（LSGA）模型，并提出了该模型下边坡稳定性系数表达式。结果表明：对于不考虑分层的无限长边坡，LSGA模型可简化为GA模型，说明GA模型是LSGA模型的一个特例；与LSGA模型相比，GA模型在失稳深度和时间上有较大延缓；饱和层渗流作用对湿润层特性影响较小，对边坡稳定性影响较大；相反，坡体长度方向尺寸效应则对湿润层特性影响明显，而对边坡稳定性影响较小；利用LSGA模型和稳定性评价方法得到的结果与模型试验揭示的现象基本吻合，证明了该方法有较好的精确性和可靠性。  相似文献   

Modeling the effect of saltation on surface layer turbulence     

Hao-Jie Huang 《地球表面变化过程与地形》2020,45(15):3943-3954

Particle–turbulence interaction has been a research focus in the field of pneumatic transport, especially in aeolian environments. However, knowledge regarding the effect of saltating particles on the turbulence characteristics is very limited. In this article, a process of sand-laden flow from forming sand streamers to stability is investigated via a coupled mathematical model of wind-blown sand that includes the spatiotemporal development. The variations in the turbulence characteristics, such as the mean velocity and turbulence intensity in clean air or sand-laden flow field, are analyzed. The results show that the splash process of sand grains near the wall decrease the wind speed in the saltation layer and destroy the low-speed streaks. Moreover, the profiles of streamwise turbulence intensity exhibit a transition from ‘decreasing’ to ‘increasing’ and approximately intersect at an ‘intensity focus’, which is presented for the first time. Furthermore, it was found that saltating particles could enhance the Reynolds stress. Meanwhile, it was also noticed that the shear stress at the wall surface is greater than the impact threshold and that there is a tendency towards the impact threshold. Therefore, saltation makes the particle Reynolds number of sand-laden flow higher than that under non-saltation conditions, thus changing the particles’ effect on the turbulence intensity. Gravity-dominated saltation is probably the most essential difference between wind-blown sand and other traditional two-phase flows. © 2020 John Wiley & Sons, Ltd.  相似文献   

城市青年群体住房产权获得的区域差异——以上海和南京为例     

崔璨  李佳怡  崔军茹  徐伟  王丰龙 《热带地理》2020,40(6):1004-1014

从城市异质性视角，以一线城市上海和二线城市南京为例，基于2013年长三角地区社会变迁调查和南京市住房调查数据，利用Logistic模型，剖析了两地青年住房产权获得的影响因素及其差异。研究发现，两个城市青年住房产权获得的影响因素存在较大差异。与南京相比，上海青年居民的住房获得存在更大的区位和制度壁垒，受城市区位、户口、制度因素影响更大，而受教育水平、工作流动性等市场因素以及年龄、是否育有子女等生命历程因素的影响较小。上海，作为一线城市，户口制度仍然处于精准严控阶段，落户门槛相对较高，另外住房价格高企，上海的青年群体在住房产权获得中同时面临着制度层面和市场层面的双重严苛考验。而在二线城市南京，户口政策相对较为宽松，青年群体的住房产权获得所面临的制度性障碍较小，而市场因素更加主导。  相似文献   

高速影像中风沙颗粒灰度和表观粒径的变化特征及对多假设追踪算法的意义     

梅凡民  张梦莲 《中国沙漠》2019,39(3):7-16

沙粒轨迹形成过程是理解风沙两相流输运力学机制的关键问题。多假设追踪算法通过融合追踪目标的多个信息特征和建立后验概率控制的动态递归算法来实现对目标的准确追踪，其精度可能优于传统的基于位置信息的轨迹追踪算法。基于多假设追踪算法的需要，以沙粒灰度和表观粒径（沙粒在影像上显现的大小）为对象，通过分析沙粒在轨迹形成过程中灰度和表观粒径的辨识度及稳定性来揭示它们作为多假设轨迹算法的特征参数的可能性和可靠性。结果表明：沙粒灰阶25~255，具有多峰分布的特征，表明不同沙粒灰度具有很好的区分度；80%~85%的沙粒在入射、反弹过程及粒-床碰撞后，灰度差在1倍标准偏差之内，表明大多数沙粒的灰度具有相对的稳定性；沙粒的表观粒径分布于77~1 001 μm，表明表观粒径具有较好的区分度；97%~100%的沙粒在入射、反弹过程中、77%的沙粒在粒-床碰撞后，表观粒径差均是稳定的（77~154 μm）；仅有15%~23%的沙粒发生了显著的侧向运动或自旋，表明多数沙粒的灰度和表观粒径的稳定性不受侧向运动或自旋的影响；灰度和表观粒径可以作为多假设追踪算法的重要辨识参数。  相似文献   

Assessing the South African sardine resource: two stocks rather than one?     

CL de Moor  DS Butterworth 《African Journal of Marine Science》2015,37(1):41-51

Sardine Sardinops sagax distributed off the west and south coasts of South Africa have traditionally been assumed to comprise a single well-mixed stock for assessment and management purposes. New research, however, lends weight to the possibility of two stocks in this region. A precautionary management approach thus needs to consider the impact of management decisions on the hypothesised two individual stocks as well as on the resource as a whole. As a first step in this process, Bayesian assessments of South African sardine are presented, which compare results for the traditional single-stock hypothesis with those that follow from a new two-mixing-stock hypothesis. Recruits from the west stock are assumed to move to and remain part of the south stock in annual pulses of varying size. This movement is estimated to be appreciable, and to take place from a substantially more productive west stock to the south stock. This immigration makes a greater contribution to the south-stock biomass than do years of above-average south-stock recruitment. Importantly, this two-mixing-stock hypothesis is shown to be consistent with the data available. Further alternative sardine stock-structure hypotheses suggested by the most recent data are discussed.  相似文献   

Impact of Analysis-time Tuning on the Performance of the DRP-4DVar Approach     

ZHAO Juan  WANG Bin  LIU Juanjuan 《大气科学进展》2011,28(1):207-216

In this study we extend the dimension-reduced projection-four dimensional variational data assimilation (DRP-4DVar) approach to allow the analysis time to be tunable, so that the intervals between analysis time and observation times can be shortened. Due to the limits of the perfect-model assumption and the tangentlinear hypothesis, the analysis-time tuning is expected to have the potential to further improve analyses and forecasts. Various sensitivity experiments using the Lorenz-96 model are conducted to test the impact of analysistime tuning on the performance of the new approach under perfect and imperfect model scenarios, respectively. Comparing three DRP-4DVar schemes having the analysis time at the start, middle, and end of the assimilation window, respectively, it is found that the scheme with the analysis time in the middle of the window outperforms the others, on the whole. Moreover, the advantage of this scheme is more pronounced when a longer assimilation window is adopted or more observations are assimilated.  相似文献   

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王伟  李迪贵 《大地测量与地球动力学》2015,35(2):232-234

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Rating curve uncertainty and change detection in discharge time series: case study with 44‐year historic data from the Nyangores River,Kenya          下载免费PDF全文

John Juston  Per‐Erik Jansson  David Gustafsson 《水文研究》2014,28(4):2509-2523

The intersection of the developing topic of rating curve and discharge series uncertainty with the topic of hydrological change detection (e.g., in response to land cover or climatic change) has not yet been well studied. The work herein explores this intersection, with consideration of a long‐term discharge response (1964–2007) for a ~650‐km² headwater basin of the Mara River in west Kenya, starting with stream rating and daily gauge height data. A rating model was calibrated using Bayesian methods to quantify uncertainty intervals in model parameters and predictions. There was an unknown balance of random and systemic error in rating data scatter (a scenario not likely unique to this basin), which led to an unknown balance of noise and information in the calibrated statistical error model. This had implications on testing for hydrological change. Overall, indications were that shifts in basin's discharge response were rather subtle over the 44‐year period. A null hypothesis for change using flow duration curves (FDCs) from four different 8‐year data intervals could be either accepted or rejected over much of the net flow domain depending on different applications of the statistical error model (each with precedence in the literature). The only unambiguous indication of change in FDC comparisons appeared to be a reduction in lowest baseflow in recent years (flows with >98% exceedance probability). We defined a subjective uncertainty interval based on an intermediate balance of random and systematic error in the rating model that suggested a possibility of more prevalent impacts. These results have relevance to management in the Mara basin and to future studies that might establish linkages to historic land use and climatic factors. The concern about uncertain uncertainty intervals (uncertainty²) extends beyond the Mara and is relevant to testing change where non‐random rating errors may be important and subtle responses are investigated. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

整合等级与顺序的黄土高原小流域沟道结构理论研究     

王道军  龚建华  马蔼乃  李文航 《地理与地理信息科学》2007,23(4):1-4

沟道等级结构与顺序结构都可看作是沟道拓扑结构,在黄土高原小流域坝系规划研究中,往往需要将Horton-Strahler的沟道分级模型与较长沟道优先的顺序编码模型进行整合。该文提出一个沟道结构假说,即在黄土高原小流域尺度上,存在一个最小集水面积与最短沟道长度的适宜取值区间,使得基于DEM提取的沟道网络上任意节点对应的较长沟道作为主沟道,其Horton-Strahler沟道等级不低于汇入支流。搜集的黄土高原丘陵沟壑区多个副区的一些典型小流域数据有效验证了上述假说,从而为实现整合等级结构与顺序结构的沟道编码模型的进一步研究提供理论基础。  相似文献   

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张凯  赵建虎  陈卓 《大地测量与地球动力学》2014,34(1):123-126

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