受冲击荷载作用土体变形的有限元研究

把土当作一种弹塑性材料,把钻头冲击土体的过程抽象为一个半无限体在圆环面积上受均布力作用的问题,建立合理的计算模型,采用ANSYS有限元分析中瞬时动态动力学分析来模拟分析土体冲击变形过程,探讨在钻头结构一定、输出一定的冲击功的条件下,其所能切入土层的深度和钻头对柱状土心的扰动情况。经分析得出,土体轴向压缩量在钻头底唇面处最大,在土样中心部位最小;钻头内外壁和土层接触处土中的密塞斯应力几乎是突变的,而应力在土样中几乎都保持在最小值的水平;冲击对土样的扰动只是在一个很小的范围内。     

阻尼对行车荷载下大跨桥梁振动的影响

基于车桥相互作用,建立了车桥耦合单元,一个车辆模拟为4轴10个自由度模型,桥梁模拟为梁单元,推导出列车桥梁整体系统运动方程的有限元计算公式.采用随机数值模拟方法和功率谱密度函数生成随机轨道粗糙度.编制了计算程序,考虑各种不同的阻尼参数及车辆速度,对一座实际大跨斜拉桥的动力反应与冲击效应进行了分析研究.     

中国互联网发展的区域差异分析

互联网发展的区域差异及其与区域发展的相互影响研究已成为地理学研究中一个新的问题。从网络普及率、网络信息资源丰度及互联网商业应用三个角度初步探讨了中国互联网发展存在的区域差异,并设计了互联网发展指数(IDI)、从人均的角度反映互联网发展的综合水平。表明:东部地区的发展水平明显高于中部和西部地区,但与传统意义上的经济发展梯度不同的是,西部地区的互联网发展水平稍高于中部地区;中国大陆31个省、直辖市、自治区的互联网发展综合水平的差异同样显著,按照IDI值大小被划分为6个等级。互联网发展区域差异的影响因素是多方面的,应用多元回归分析方法研究发现,区域人口素质水平、区域信息和知识生产能力对我国互联网发展区域差异的解释能力最强,区域对外开放程度和区域城市化水平的影响也较显著。     

苏北地区新石器时代考古遗址分布特征及其与环境演变关系的研究

苏北地区7000-6500aB.P.青莲岗文化时期重要新石器遗址有18处,主要分布在苏北废黄河泗阳至涟水段南北两岸。6000-5200aB.P.刘林文化时期重要遗址有9处,主要分布在涟水、邳县和高邮等地。6300-4400aB.P.大汶口文化时期主要遗址有8处,4100-3800aB.P.龙山文化时期主要遗址有23处,这两个时期遗址主要分布于连云港-沭阳-泗洪一线以西。以上遗址分布与气候和海面变化密切相关:7000aB.P.前的全新世最大海侵使江苏沿海普遍遭到海侵,故本区未发现7000aB.P.前的新石器遗址;青莲岗文化遗址多分布在基本未受海侵影响的陆相环境区;刘林文化遗址的锐减预示着5500aB.P.前后苏北全新世高海面的到来;龙山文化时期苏北大部分成陆,使得遗址数量增加更为显著。     

Homogenization of spatial patterns of hydrologic response in artificially drained agricultural catchments

Anthropogenic modifications to the landscape, with agricultural activities being a primary driver, have resulted in significant alterations to the hydrologic cycle. Artificial drainage, including surface and subsurface drainage (tile drains), is one of the most extensive manipulations in agricultural landscapes and thus is expected to provide a distinct signature of anthropogenic modification. This study adopts a data synthesis approach in an effort to characterize the signature of artificial subsurface drainage. Daily discharge data from 24 basins across the state of Iowa, which encapsulate a range of anthropogenic modifications, are assessed using a variety of flow metrics. Results indicate that the presence of artificial subsurface drainage leads to a homogenization of landscape hydrologic response. Non‐tiled watersheds exhibit a decrease in the area‐normalized peak discharge and an increase in the baseflow ratio (baseflow/streamflow) with increases in the spatial scale, while scale invariance is apparent in tiled basins. Within‐basin variability in hydrograph recession coefficients also appears to decrease with increases in the proportion of the catchment that is artificially drained. Finally, the differences between tiled and non‐tiled landscapes disappear at scales greater than approximately 2200 km², indicating that this may be a threshold scale for studying the effects of tile drainage. This decrease in within‐basin variability and the scale invariance of hydrologic metrics in artificially drained watersheds are attributed to the creation of a bypass flow hydrologic pathway that bypasses the complexity of the catchment travel paths. Spatial homogeneity in responses implies that it may be possible to develop more parsimonious hydrologic models for these regions. Copyright © 2013 John Wiley & Sons, Ltd.     

The metahyaloclastitic matrix of a unique metavolcanic block reveals subduction in the Somozas Mélange (Cabo Ortegal Complex,NW Iberia): tectonic implications for the assembly of Pangea

The allochthonous Cabo Ortegal Complex (NW Iberian Massif) contains a ~500 m thick serpentinite‐matrix mélange located in the lowest structural position, the Somozas Mélange. The mélange occurs at the leading edge of a thick nappe pile constituted by a variety of terranes transported to the East (present‐day coordinates; NW Iberian allochthonous complexes), with continental and oceanic affinities, and represents a Variscan suture. Among other types of metaigneous (calcalkaline suite dated at 527–499 Ma) and metasedimentary blocks, it contains close‐packed pillow‐lavas and broken pillow‐breccias with a metahyaloclastitic matrix formed by muscovite–paragonite–margarite–garnet–chlorite–kyanite–hematite–epidote–quartz–rutile. Pseudosection modelling in the MnCNTKFMASHO system indicates metamorphic peak conditions of ~17.5–18 kbar and ~550 °C followed by near‐isothermal decompression. This P–T evolution indicates subduction/accretion of an arc‐derived section of peri‐Gondwanan transitional crust. Subduction below the Variscan orogenic wedge evolved to continental collision with important dextral component. Closure of the remaining oceanic peri‐Gondwanan domain and associated release of fluid led to hydration of the overlying mantle wedge and the formation of a low‐viscosity subduction channel, where return flow formed the mélange. The submarine metavolcanic rocks were deformed and detached from the subducting transitional crust and eventually incorporated into the subduction channel, where they experienced fast exhumation. Due to the cryptic nature of the high‐P metamorphism preserved in its tectonic blocks, the significance of the Somozas Mélange had remained elusive, but it is made clear here for the first time as an important tectonic boundary within the Variscan Orogen formed during the late stages of the continental convergence leading to the assembly of Pangea.     

Estimation of catchment yield and associated uncertainties due to climate change in a mountainous catchment in Australia

This paper examines the impacts of climate change on future water yield with associated uncertainties in a mountainous catchment in Australia using a multi‐model approach based on four global climate models (GCMs), 200 realisations (50 realisations from each GCM) of downscaled rainfalls, 2 hydrological models and 6 sets of model parameters. The ensemble projections by the GCMs showed that the mean annual rainfall is likely to reduce in the future decades by 2–5% in comparison with the current climate (1987–2012). The results of ensemble runoff projections indicated that the mean annual runoff would reduce in future decades by 35%. However, considerable uncertainty in the runoff estimates was found as the ensemble results project changes of the 5^th (dry scenario) and 95^th (wet scenario) percentiles by ?73% to +27%, ?73% to +12%, ?77% to +21% and ?80% to +24% in the decades of 2021–2030, 2031–2040, 2061–2070 and 2071–2080, respectively. Results of uncertainty estimation demonstrated that the choice of GCMs dominates overall uncertainty. Realisation uncertainty (arising from repetitive simulations for a given time step during downscaling of the GCM data to catchment scale) of the downscaled rainfall data was also found to be remarkably high. Uncertainty linked to the choice of hydrological models was found to be quite small in comparison with the GCM and realisation uncertainty. The hydrological model parameter uncertainty was found to be lowest among the sources of uncertainties considered in this study. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrologic processes that govern stormwater infrastructure behaviour

Using water budget data from published literature, we demonstrate how hydrologic processes govern the function of various stormwater infrastructure technologies. Hydrologic observations are displayed on a Water Budget Triangle, a ternary plot tool developed to visualize simplified water budgets, enabling side‐by‐side comparison of green and grey approaches to stormwater management. The tool indicates ranges of hydrologic function for green roofs, constructed wetlands, cisterns, bioretention, and other stormwater control management structures. Water budgets are plotted for several example systems to provide insight on structural and environmental design factors, and seasonal variation in hydrologic processes of stormwater management systems. Previously published water budgets and models are used to suggest appropriate operational standards for several green and grey stormwater control structures and compare between conventional and low‐impact development approaches. We compare models, characterize and quantify water budgets and expected ranges for green and grey infrastructure systems, and demonstrate how the Water Budget Triangle tool may help users to develop a data‐driven approach for understanding design and retrofit of green stormwater infrastructure.     

Improvement of SWAT2000 modelling to assess the impact of dams and sluices on streamflow in the Huai River basin of China

Hydrological simulation and assessment in a dam–sluice regulated river basin are a complex and challenging issue. In this article, an improved SWAT2000 modelling system was developed that incorporated the Shuffled complex evolution (SCE‐UA) optimization algorithm and the multi‐site and multi‐objective calibration strategy. The implication of multi‐objective is different for different types of outlets, i.e. streamflow for an ordinary outlet, inflow for a sluice, and water storage for a reservoir. Model parameters were redefined to improve model simulations. The surface runoff lag time (SURLAG) was extended as a spatially distributed parameter, and a correction coefficient was introduced to modify the saturated hydraulic conductivity. The modelling system was then applied to the Huai River basin of China under various climatic conditions, including a very dry year (1999), a dry year (1981), an average year (1971), and wet year (1991). In all, 26 dams and 35 sluices were considered, among which about 20 dams/sluices were used for model calibration. The impact assessment primarily focused on the very dry year (1999). The results indicated that the released water from large reservoirs was blocked in the river channels by sluices located downstream. In the very dry year, the dam–sluice operations could result in an increase of the runoff volume during the non‐flood season and a decrease in runoff during the flood season, but the changing magnitude during the non‐flood season was much greater. An important conclusion of this case study is that the sluices in the Sha‐Yin branch located in the north region and the dams in the southern mountainous region above the Wangjiaba Hydrological Station have played the most significant role in regulating the streamflow of the entire river basin. The methods addressed in this article can simulate hydrological regime in the river basins regulated by dams and sluices under different climatic conditions at the whole‐watershed scale. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling hydrological response to a fully‐monitored urban bioretention cell

Municipalities and agencies use green infrastructure to combat pollution and hydrological impacts (e.g., flooding) related to excess stormwater. Bioretention cells are one type of infiltration green infrastructure intervention that infiltrate and redistribute otherwise uncontrolled stormwater volume. However, the effects of these installations on the rest of the local water cycle is understudied; in particular, impacts on stormwater return flows and groundwater levels are not fully understood. In this study, full water cycle monitoring data were used to construct and calibrate a two‐dimensional Richards equation model (HYDRUS‐2D/3D) detailing hydrological implications of an unlined bioretention cell (Cleveland, Ohio) that accepts direct runoff from surrounding impervious surfaces. Using both preinstallation and postinstallation data, the model was used to (a) establish a mass balance to determine reduction in stormwater return flow, (b) evaluate green infrastructure effects on subsurface water dynamics, and (c) determine model sensitivity to measured soil properties. Comparisons of modelled versus observed data indicated that the model captured many hydrological aspects of the bioretention cell, including subsurface storage and transient groundwater mounding. Model outputs suggested that the bioretention cell reduced stormwater return flows into the local sewer collection system, though the extent of this benefit was attenuated during high inflow events that may have exhausted detention capacity. The model also demonstrated how, prior to bioretention cell installation, surface and subsurface hydrology were largely decoupled, whereas after installation, exfiltration from the bioretention cell activated a new groundwater dynamic. Still, the extent of groundwater mounding from the cell was limited in spatial extent and did not threaten other subsurface infrastructure. Finally, the sensitivity analysis demonstrated that the overall hydrological response was regulated by the hydraulics of the bioretention cell fill material, which controlled water entry into the system, and by the water retention parameters of the native soil, which controlled connectivity between the surface and groundwater.