Three‐dimensional shakedown solutions for anisotropic cohesive‐frictional materials under moving surface loads     

Juan Wang  Hai‐Sui Yu 《国际地质力学数值与分析法杂志》2014,38(4):331-348

Previous work on three‐dimensional shakedown analysis of cohesive‐frictional materials under moving surface loads has been entirely for isotropic materials. As a result, the effects of anisotropy, both elastic and plastic, of soil and pavement materials are ignored. This paper will, for the first time, develop three‐dimensional shakedown solutions to allow for the variation of elastic and plastic material properties with direction. Melan's lower‐bound shakedown theorem is used to derive shakedown solutions. In particular, a generalised, anisotropic Mohr–Coulomb yield criterion and cross‐anisotropic elastic stress fields are utilised to develop anisotropic shakedown solutions. It is found that shakedown solutions for anisotropic materials are dominated by Young's modulus ratio for the cases of subsurface failure and by shear modulus ratio for the cases of surface failure. Plastic anisotropy is mainly controlled by material cohesion ratio, the rise of which increases the shakedown limit until a maximum value is reached. The anisotropic shakedown limit varies with frictional coefficient, and the peak value may not occur for the case of normal loading only. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Varying water utilization of Haloxylon ammodendron plantations in a desert‐oasis ecotone          下载免费PDF全文

Hai Zhou  Wenzhi Zhao  Gefei Zhang 《水文研究》2017,31(4):825-835

Haloxylon ammodendron is a desert shrub used extensively in China for restoring degraded dry lands. An understanding of the water source used by H. ammodendron plantations is critical achieving sustainable vegetation restoration. We measured mortality, shoot size, and rooting depth in 5‐, 10‐, 20‐, and 40‐year‐old H. ammodendron plantations. We examined stable isotopic ratios of oxygen (δ¹⁸O) in precipitation, groundwater, and soil water in different soil layers and seasons, and in plant stem water to determine water sources at different shrub ages. We found that water acquisition patterns in H. ammodendron plantations differed with plantation age and season. Thus, the main water source for 5‐year‐old shrubs was shallow soil water. Water sources of 10‐year‐old shrubs shifted depending on the soil water conditions during the season. Although their tap roots could absorb deep soil water, the plantation main water sources were from soil water, and about 50% of water originated from shallow and mid soil. This pattern might occur because main water sources in these plantations were changeable over time. The 20‐ and 40‐year‐old shrubs acquired water mainly from permanent groundwater. We conclude that the main water source of a young H. ammodendron plantation was soil water recharged by precipitation. However, when roots reached sufficient depth, water originated mainly from the deep soil water, especially in the dry season. The deeply rooted 20‐ and 40‐year‐old shrubs have the ability to exploit a deep and reliable water source. To achieve sustainability in these plantations, we recommend a reduction in the initial density of H. ammodendron in the desert‐oasis ecotone to decelerate the consumption of shallow soil water during plantation establishment.  相似文献   

δ18O and δ13C in fossil shells of Radix sp. from the sediment succession of a dammed palaeo‐lake in the Yarlung Tsangpo valley,Tibet, China     

Hai‐Ping Hu  Jin‐Liang Feng  Feng Chen 《Boreas: An International Journal of Quaternary Research》2017,46(3):412-427

A series of confirmed and suspected dammed palaeo‐lake sedimentary successions is scattered within the middle Yarlung Tsangpo valley in Tibet. However, the chronology, the genesis of the dam and its location, the water level of the dammed lake, the process of dam failure and the spatiotemporal relationships between the sedimentary successions remain controversial. Here, we focus on one sedimentary succession of the suspected dammed palaeo‐lake at Xigazê. We measured the grain‐size distribution, magnetic susceptibility, organic and inorganic carbon content, and δ¹³C_org and δ¹⁵N_total ratios of the sediments. In addition, we measured the δ¹⁸O_shell and δ¹³C_shell values of modern and fossil Radix sp. shells, and the δ¹⁸O_water and δ¹³C_DIC values of the ambient water with different hydrological regimes. The results indicate that the δ¹⁸O_shell values of modern Radix sp. and the δ¹⁸O_water of the ambient water body significantly depend on its hydrological status. In addition, a strong positive relationship was observed between δ¹⁸O_shell values of modern Radix sp. shells and the δ¹⁸O_water of the ambient water on the Tibetan Plateau. According to this correlation, the δ¹⁸O_water values of the palaeo‐water body are reconstructed using the δ¹⁸O_shell values of Radix sp. fossil shells in the Xigazê section. Further, based on the δ¹⁸O_shell values of fossil Radix sp., the reconstructed δ¹⁸O_water of the palaeo‐water body and the specific habitats of Radix sp., we infer that the sedimentary succession in the Xigazê broad valley was mainly formed within the backwater terminal zone of a dammed palaeo‐lake and that the elevation of the water level of the lake was approximately 3811 m a.s.l. AMS ¹⁴C dating indicates that the deposits of the dammed palaeo‐lake were formed at about 33–22 cal. ka BP. Finally, the presence of Radix sp. fossil shells within the Xigazê section suggests that Radix sp. survived the late Last Glacial Period on the Tibetan Plateau.  相似文献   

测绘地物波谱本底数据库     

钟守熠  肖青  闻建光  郑兴明  马明国  屈永华  郑柯  池天河  唐勇  游冬琴  郝大磊  程娟  贺敏  姜涛  晋锐  姚晓婧  赵理君 《遥感学报》2020,24(6):701-716

地物波谱特性是利用遥感进行建模反演和地物目标探测识别的理论基础，波谱数据库对于提高遥感应用水平有重要作用。为规范和丰富中国波谱数据库并促进其在测绘等领域的应用，依托国家科技性基础专项,建立了“测绘地物波谱本底数据库”，在数据规范编制、波谱数据采集实验与整编入库、地物波谱数据库建设和应用示范初步探索方面取得重要进展。在波谱数据采集和处理的标准规范方面，建立完善了测绘地物波谱与配套非波谱数据收集与汇总标准、测绘地物波谱和配套非波谱参数测试技术规范、测绘地物波谱库地物分类编码规范。依照项目制定的数据规范标准，对现有波谱数据进行了整编和入库，共计整编数据1.4万余条；组织实施了全国范围的典型地物波谱采集实验以及相应配套参数测量实验，主要试验类型包括典型地物波谱测量试验、定点时间序列测量试验、多尺度测量试验、全波段测量试验、参数控制测量试验和无人机观测试验等，共计获取地物波谱1.7万余条。特别是在华北和东北进行了全波段观测试验（可见光—近红外波（0.35—2.5 μm）、红外波段（3—15 μm）、微波波段（Ka、K、X、C、L波段）），获取冰雪、土壤、植被冠层、人工目标的全波段数据。为方便波谱数据的应用和共享，项目建设了包含3万余条数据的测绘地物波谱本底数据库（GOSPEL）及数据共享平台。依据地物波谱数据的类型和应用需求，形成了全波段典型地物波谱数据集、多角度光谱反射率数据集、多尺度典型地物反射率数据集、长时间系列波谱数据集等共25个特色数据集。基于测绘地物波谱本底数据库进行了地物分类、遥感机理模拟、遥感定量反演、遥感产品验证等方面的应用示范。  相似文献   

从地理信息系统到虚拟地理环境的认知转变     

林珲  胡明远  陈旻  张帆  游兰  陈宇婷 《地球信息科学学报》2020,22(4):662-672

自20世纪60年代初以来,地理信息系统引领了地理信息的分析与服务。然而,由于地理学家对于地理过程开展多维模拟的需求,同时许多大型工程需要对于不同方案的后果事先开展模拟评估,为此中国学者们在世纪相交之际开始了对于虚拟地理环境的探索。本文从地理信息系统到虚拟地理环境的认识上的转变着手,分析了虚拟地理环境的演进过程、当前的阶段定位与挑战,着重探讨了虚拟地理环境研究的新态势：基于虚拟地理环境的地理空间认知研究、虚拟地理环境与实验地理学新方向、大数据背景下的虚拟地理认知实验方法和虚拟地理环境与地理知识工程,并给出最新研究思路。  相似文献   

Application of flocculation combined with vacuum preloading to reduce river-dredged sludge     

Feiyu Liu  Wenqing Wu  Jun Wang  Jun Hai  Yuanqiang Cai 《Marine Georesources & Geotechnology》2020,38(2):164-173

Abstract

To achieve the rapid dewatering of dredged sludge, the flocculation–vacuum-preloading method was tested indoors. In this study, the optimal mixing ratio of six flocculants was determined through the settling column test, and then the proposed method was tested. The water drainage and settlement were monitored during the test, while the soil moisture content and shear strength were measured after the test. The results show that all the flocculants had an optimal mixing ratio, and the addition of 0.8% FeCl₃ or 0.08% anionic polyacrylamide (APAM) in the sludge can better accelerate solid–liquid separation of the sludge. After the test, the water content in the sludge decreased from 140% to 60%. Compared with general vacuum preloading, the use of the proposed method increased the water drainage by 46.5% and 56.8% and decreased the soil volumes by 60.5% and 82.4% for FeCl₃ and APAM, respectively. Moreover, the corresponding shear strength was increased from 10 to 14 and 17?kPa. In addition, the use of APAM increased the solidification rate of heavy metals in the sludge to more than 80%, effectively inhibiting the migration of heavy metals.  相似文献   

A two‐dimensional coupled hydromechanical discontinuum model for simulating rock hydraulic fracturing          下载免费PDF全文

Yu‐Yong Jiao  Huan‐Qiang Zhang  Xiu‐Li Zhang  Hai‐Bo Li  Qing‐Hui Jiang 《国际地质力学数值与分析法杂志》2015,39(5):457-481

Within the framework of our discontinuous deformation analysis for rock failure algorithm, this paper presents a two‐dimensional coupled hydromechanical discontinuum model for simulating the rock hydraulic fracturing process. In the proposed approach, based on the generated joint network, the calculation of fluid mechanics is performed first to obtain the seepage pressure near the tips of existing cracks, and then the fluid pressure is treated as linearly distributed loads on corresponding block boundaries. The contribution of the hydraulic pressure to the initiation/propagation of the cracks is considered by adding the components of these blocks into the force matrix of the global equilibrium equation. Finally, failure criteria are applied at the crack tips to determine the occurrence of cracking events. Several verification examples are simulated, and the results show that this newly proposed numerical model can simulate the hydraulic fracturing process correctly and effectively. Although the numerical and experimental verifications focus on one unique preexisting crack, because of the capability of discontinuous deformation analysis in simulating block‐like structures, the proposed approach is capable of modeling rock hydraulic fracturing processes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

出租车轨迹数据挖掘进展   总被引：1，自引：0，他引：1  

吴华意  黄蕊  游兰  向隆刚 《测绘学报》2019,48(11):1341-1356

大数据、物联网与精密定位技术的发展推动了城市感知的进步。随着社会活动的与日俱增,出租车轨迹数据不仅记录了出租车的行车轨迹,还蕴藏着道路交通状态、城市居民出行规律、城市结构及其他社会问题。通过各种数据分析与挖掘手段对出租车轨迹数据进行深入探究,对于智能交通、城市规划等有着重要意义。本文综述了近十年国内外基于出租车轨迹大数据的相关研究,按照空间统计方法、时间序列方法、图论与网络方法及机器学习方法等4类,详细阐述各类方法的研究现状。随后,本文分析了现有研究的应用领域、热点主题和发展趋势。最后,本文指出了出租车轨迹数据挖掘研究领域面临的挑战和未来研究方向。  相似文献   

Wave Attenuation Performance and the Influencing Factors of A Lower Arc-Plate Breakwater     

LI Xue-yan  WANG Qing  YOU Zai-jin  GUO Wei-jun  ZHANG Jun-bin  ZHAN Chao  ZHANG Zhi-chen  WANG Li-xue  LI Qin 《中国海洋工程》2020,(1):89-98

Comprehensive experimental and numerical studies have been undertaken to investigate wave energy dissipation performance and main influencing factors of a lower arc-plate breakwater. The numerical model, which considers nonlinear interactions between waves and the arc-plate breakwater, has been constructed by using the velocity wave- generating method, the volume of fluid (VOF) method and the finite volume method. The results show that the relative width, relative height and relative submergence of the breakwater are three main influencing factors and have significant influence on wave energy dissipation of the lower arc-plate open breakwater. The transmission coefficient is found to decrease with the increasing relative width, and the minimum transmission coefficient is 0.15 when the relative width is 0.45. The reflection coefficient is found to vary slightly with the relative width, and the maximum reflection coefficient is 0.53 when the relative width is 0.45. The transmission and reflection coefficients are shown to increase with the relative wave height for approximately 85% of the experimental tests when the relative width is 0.19 0.45. The transmission coefficients at relative submergences of 0.04, 0.02 and 0 are clearly shown to be greater than those at relative submergences of 0.02 and 0.04, while the reflection coefficient exhibits the opposite relationship. After the wave interacts with the lower arc-plate breakwater, the wave energy is mainly converted into transmission, reflection and dissipation energies. The wave attenuation performance is clearly weakened for waves with greater heights and longer periods.  相似文献   

Analytical method of radiation by a wave energy device with dual rectangular floating bodies     

WANG Wensheng  YOU Yage  ZHANG Yunqiu  WU Bijun  YE Yin 《海洋学报(英文版)》2010,29(3):106-115

The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.  相似文献